http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25669 The geochemical “arc signature” has been largely interpreted as reflecting a mantle source contaminated by fluids and sediments released by the subducted slab. Amongst intra-oceanic arcs, the Lesser Antilles displays some of the most extreme chemical and isotopic variations ranging from fluid-modified MORBs to compositions approaching that of continental crust [1]. The extreme range in geochemistry might result from sediments subducted into the mantle source [2], assimilation of sediments in the arc crust [1], or both. This debate, first outlined in 1984, has still not been resolved since the different tools used up to now have led to conflicting conclusions. The relative role of source contamination by subducted material and magma-arc crust interaction may be constrained by using a multiscale isotopic and chemical approach from whole rock to sub-mineral scale on stratigraphically-constrained samples from a single locality. To do this, we chose the island of St Lucia, specifically its Soufriere Volcanic Complex (SVC) since, according to preliminary data, it displays one of the largest ranges of radiogenic isotope ratios in the arc. Our preliminary whole rock trace element and isotopic data confirm that St Lucia displays most of the compositional range observed at the whole arc. There are two distinct groups: the Pre-Soufrière Volcanic Complex (SVC) and the SVC itself. The Pre-SVC group comprises the oldest, most mafic rocks of the island and has typical intra-oceanic arc signatures (e.g. 87Sr/86Sr = 0.70439-0.70413) similar to compositions observed in the north of the arc. Despite following the same differentiation trend as the Pre-SVC (suggesting a common source), the younger SVC rocks are more felsic and display extreme crustal signatures (e.g. 87Sr/86Sr = 0.70754-0.70906) more typically observed in continental arcs. At the mineral scale, plagioclase, quartz, pyroxene and amphibole separates from the SVC lavas all display strong crustal signatures with δ18O compositions much higher than the ranges in equilibrium with the mantle (9.92-11.1, 10.6-11, 9-9.5, 9.4-9.8‰VSMOW, respectively). Such high values have never been reported in intra-oceanic arcs lacking known continental basement and strongly argue for assimilation of sediments during ascent and storage of the magmas. Sr isotopic analyses of single plagioclases support crustal assimilation since different crystals within the same sample are isotopically distinct. Submineral scale analysis should refine these interpretations. 2013-05-22T06:15:01.569Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25646 6 page(s) 2013-05-20T06:00:14.169Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25645 In order to shed light on the cause for onset of strain localisation in plagioclase-rich rocks we have performed detailed microstructural analyses on a sheared anorthosite-leucogabbro using optical microscopy, electron backscatter diffraction (EBSD) and chemical analyses. The analysed sample is from an Archaean unit, SW Greenland, deformed at lower to mid crustal conditions (T = 675-700 °C and moderate pressure). The initial deformation occurred dominantly by dislocation creep and the grain size was reduced primarily by subgrain rotation recrystallisation. Recrystallised plagioclase grains (average size 80 μm) are dominantly found in (i) clusters, (ii) lenses and (iii) continuous bands subparallel to shear zone boundaries. Recrystallised grains in clusters and lenses display inherited crystallographic orientations. Their bulk crystallographic preferred orientation (CPO) is random; however, crystallographic characteristics show that parent and daughter grains have the same misorientation axes and possibly the same active slip systems. Recrystallised grains in continuous bands show a CPO with a single dominant active slip system, (001)<110>, aligned with the structural (XYZ) framework. For these parent and daughter grains, misorientation axes are random and the dominant slip system is different. Grain rotations of recrystallised grains are traceable back to the orientation of the adjacent porphyroclast. We infer that the cause for strain localisation is recrystallisation and development of a CPO in continuous recrystallised bands. 2013-05-20T06:00:13.430Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25641 An asymmetric binary Margules formulation for excess Gibbs energy, enthalpy, and entropy is adequate to describe the 1 bar halite-sylvite solvus in NaCl-KCl (Thompson and Waldbaum 1969). However, a binary Margules formulation is not adequate to describe excess volumes of single-phase chlorides in P-V-T-X from ambient P-T to ∼20 kbar and 700 °C. Excess volumes across NaCl-KCl increase with temperature, decrease with pressure, and show systematic deficits in the consolute region. These patterns can be explained by the importance of a third component - vacancy defects that relieve the lattice stresses of K-Na size mismatch. New, two-phase observations in P-V-T-X allow delineation of the excess Gibbs energies to high pressures where the excess enthalpies and entropies do not depend on T at each P, but show significant variation between 1 bar and ∼20 kbar. The volume, entropy, and enthalpy of K-Na mixing become more ideal at high pressure. But the solvus expands with pressure because entropy approaches ideality faster than enthalpy and, therefore, Gibbs energy of K-Na mixing becomes less ideal with pressure. The consolute temperature rises about 80 ° C in 17 kbar, with little change in consolute composition. The binary Margules equation of state provides a prediction of the rise of the solvus that is impressively convergent with the new observations. This convergence is especially impressive given the clear inadequacies of the binary excess volume formulation on which the prediction is based. 2013-05-20T05:30:13.491Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25640 Quartz crystallographic preferred orientations (CPO) from three distinct orthogneisses using both the Electron Back Scatter Diffraction (EBSD) and Fabric Analyser (FA) techniques reveal a clear trend from basal and rhomb slip for high P-T conditions (670 ± 20 °C/9 kbar), rhomb and basal slip for medium P-T (590 ± 15 °C/6 kbar) and a dominance of prism slip for lower P-T conditions (<570 °C/4-5 kbar). The textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences. Locally quartz CPOs are different within one thin section, and in comparison to bulk orientation measurements both, EBSD and the Fabric Analyser techniques are ideal to determine such textural heterogeneities. While the EBSD is a powerful technique to determine the full CPO, measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the FA is an accurate tool to determine CPOs of c-axis orientations in uniaxial materials. In a CPO focussed study the FA is a cheap alternative to EBSD as the analysis of whole thin section can be accomplished in a very short time, with minimal sample preparation. With the FA it is possible to evaluate the CPOs of several samples quickly with an accuracy that allows id entification of the main slip systems and their homogeneity. 2013-05-20T05:00:08.793Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25636 The crystallization mechanism in cordierite glass (Mg₂Al₄Si₅O₁₈) doped with 0.34 mol% Cr₂O₃ has been studied in detail with in situ small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) and ex situ Cr X-ray absorption fine structure (XAFS). The crystalline component comprises an alumino-chromate spinel precipitating within the bulk together with an independent silica-rich stuffed quartz phase that appears to nucleate from the specimen surface. By employing a double heat treatment close to the glass transition, finely dispersed spherical crystallites of a alumino-chromate spinel are grown from Cr nucleating sites. The total crystallized volume of around 4% and the composition of the spinel, MgCr₀․₁₈Al₁․₈₂O₄, are directly related to the Cr content in the starting glass. Moreover, the alumino-chromate particles are found to be closely monodispersed partway through the crystallization process, growing from rough crystallites to smooth particles of radius 210 ± 20 Å, with a final bulk particle density of 1.21 ± 0.4 × 10¹⁵ cm⁻³. Growth is limited by diffusion in the soft glass and is complete when all the available Cr is exhausted. The advantages of in situ combined scattering diffraction and spectroscopy for probing the nanostructure crystallography and local atomic structure in the formation of ceramics the order in which events take place and the insights this gives in the underlying physical processes are stressed. 2013-05-20T04:43:58.594Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25633 The possibility of using X-ray diffraction to precisely monitor crystal structure at the extremes of pressure and temperature produced by shock-wave loading is explored. A summary of the advantages of using various X-ray sources for this work and an outline of the necessary experimental layout is given. 2013-05-20T04:10:09.515Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25632 A new facility for high-pressure diffraction and spectroscopy using diamond anvil high-pressure cells has been built at the Advanced Light Source on beamline 12.2.2. This beamline benefits from the hard X-radiation generated by a 6 T superconducting bending magnet (superbend). Useful X-ray flux is available between 5 keV and 35 keV. The radiation is transferred from the superbend to the experimental enclosure by the brightness-preserving optics of the beamline. These optics are comprised of a plane parabola collimating mirror, followed by a Kohzu monochromator vessel with Si(111) crystals (E/ΔE≃7000) and W/B₄C multilayers (E/ΔE≃100), and then a toroidal focusing mirror with variable focusing distance. The experimental enclosure contains an automated beam-positioning system, a set of slits, ion chambers, the sample positioning goniometry and area detector (CCD or image-plate detector). Future developments aim at the installation of a second endstation dedicated to in situ laser heating and a dedicated high-pressure single-crystal station, applying both monochromatic and polychromatic techniques. 2013-05-20T04:00:12.683Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25627 The size trend for the pressure-induced γ-Fe₂O₃ (maghemite) to α-Fe₂O₃ (haematite) structural phase transition in nanocrystals has been observed. The transition pressure was found to increase with decreasing nanocrystal size: 7 nm nanocrystals transformed at 27 ± 2 GPa, 5 nm ones at 34 ± 3 GPa and 3 nm ones at 37 ± 2 GPa. Annealing of a bulk sample of γ-Fe₂O₃ was found to reduce the transition pressure from 35 ± 2 to 24 ± 2 GPa. The bulk modulus was determined as 262 ± 6 GPa for 7 nm nanocrystals of γ-Fe₂O₃, which is significantly higher than the value of 190 ± 6 GPa that we measured for bulk samples. For α-Fe₂O₃, the bulk moduli for 7 nm nanocrystals (336 ± 5) and the bulk (300 ± 30) were found to be almost the same within error. The bulk modulus for the γ phase was found to decrease with decreasing particle size between 10 and 3.2 nm particle size. Values for the ambient pressure molar volume were found within 1% to be: 33.0 cm3 mol⁻¹ for bulk γ-Fe₂O₃; 32.8 cm³ mol⁻¹ for 7 nm diameter γ-Fe₂O₃ nanocrystals; 30.7 cm³ mol⁻¹ for bulk α-Fe₂O₃; and 30.6 cm³ mol⁻¹ for α-Fe₂O₃ nanocrystals. 2013-05-20T02:40:12.557Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25626 High-pressure Mössbauer spectroscopy on several compositions across the (Mg,Fe)O magnesiowüstite solid solution confirms that ferrous iron (Fe²⁺) undergoes a high-spin to low-spin transition at pressures and for compositions relevant to the bulk of the Earth's mantle. High-resolution x-ray diffraction measurements document a volume change of 4-5% across the pressure-induced spin transition, which is thus expected to cause seismological anomalies in the lower mantle. The spin transition can lead to dissociation of Fe-bearing phases such as magnesiowüstite, and it reveals an unexpected richness in mineral properties and phase equilibria for the Earth's deep interior. 2013-05-20T02:00:17.974Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25625 Experimentally determined phase relations in the system MgO-AlO₁․₅-SiO₂ at pressures relevant to the upper part of the lower mantle indicate that Mg-silicate perovskite incorporates aluminum into its structure almost exclusively by a charge-coupled reaction. MgSiO₃-rich bulk compositions along the joins MgSiO₃-MgAlO₂․₅ and MgSiO₃-MgAl₂O₄ crystallize assemblages of perovskite coexisting with periclase. MgO-saturated perovskites along these joins have ambient unit cell volumes consistent with those measured and calculated for aluminous perovskite along the charge-coupled substitution join, MgSiO₃-AlO₁․₅. The compressibility of aluminous perovskite along the MgO-saturated joins is not anomalously low as predicted for oxygen-defect perovskites. The bulk moduli, however, are consistent with previous measurements made for aluminous perovskites along the charge-coupled substitution join. These results agree with first-principles calculations showing very limited stability of O-defects in Mg-perovskite at pressures and temperatures corresponding to lower mantle conditions, but are inconsistent with earlier experimental results showing unusually compressive aluminous perovskite. The maximum solubility of alumina in perovskite is ∼25 mol% along the MgSiO₃-AlO₁․₅ join within the ternary MAS-system (i.e. pyrope composition), and the join is apparently binary. Although primitive mantle peridotite compositions are MgO-saturated and fall nearly on the oxygen vacancy join, alumina substitution into perovskite is expected to occur primarily by charge-coupled substitution throughout the lower mantle. The compressibility of aluminous perovskite in primitive mantle is expected to be only a few percent lower than for end member MgSiO₃ perovskite. 2013-05-20T01:50:10.580Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25584 A program for the automation of the processing of powder diffraction data collected from an area detector is presented in this article. Encapsulation of existing software packages in wrapper programs can allow automation and linking of existing well-proven computer code. This eliminates the need to reinvest resources in developing new codes to meet evolving scientific needs. Here, we demonstrate this principle by automating the use of two programs commonly used in the processing of powder diffraction data from area detectors: fit2d and GSAS. 2013-05-16T08:11:31.001Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25585 High-pressure angle-dispersive X-ray diffraction measurements show that Cd₀․₈₀Hg₀․₂₀ alloy remains in the hcp structure up to 50 GPa. We observe subtle anomalies in the pressure variation of the lattice parameters and their ratio, and in normalized stress versus strain. Electronic-structure calculations, as well as experimental and theoretical results for Cd, suggest that these anomalies are related to the occurrence of electronic topological transitions. Our results support Lifshitz's prediction that electronic phase transitions can cause anomalies in structural and elastic properties of materials. 2013-05-16T08:11:28.250Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25590 Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years. 2013-05-16T08:11:15.047Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25592 X-ray diffraction measurements of natural talc plus water at combined pressures and temperatures of 0-15 GPa and 23-400 °C reveal the presence of a structural change that could be interpreted as a new high-pressure phase at 4.0 (±.5) GPa, and raise the possibility that the newly inferred phase transition takes place in cold subducting slabs as a precursor to appearance of the 10 Å phase of talc. 2013-05-16T08:11:06.778Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25594 X-ray diffraction and infrared data have been collected from a sample of ettringite from ambient pressure to 6.4 GPa. The sample was found to reversibly transform to an amorphous phase at 3 GPa. The isothermal bulk modulus of ettringite was found to be 27(7) GPa and the incompressibilities of the lattice parameters were found to be 71(30) GPa along a and 108(36) GPa along c. 2013-05-16T08:11:01.750Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25596 The laser-heating system for the diamond anvil cell at endstation 2 of beamline 12.2.2 of the Advanced Light Source in Berkeley, CA, has been constructed and is available for in situ high-pressure high-temperature X-ray experiments. The endstation couples a high-brilliance synchrotron X-ray source with an industrial strength laser to heat and probe samples at high pressure in the diamond anvil cell. The system incorporates an 50 W Nd:YLF (cw) laser operated in TEM01* mode. Double-sided heating is achieved by splitting the laser beam into two paths that are directed through the opposing diamond anvils. X-ray transparent mirrors steer the laser beams coaxial with the X-ray beam from the superconducting bending magnet (energy range 6-35 KeV) and direct the emitted light from the heated sample into two separate spectrometers for temperature measurement by spectroradiometry. Objective lenses focus the laser beam to a size of 25 μm diameter (FWHM) in the sample region. An X-ray spot size of 10 μm diameter (FWHM) has been achieved with the installation of a pair of focusing Kirkpatrick-Baez mirrors. A unique aperture configuration has produced an X-ray beam profile that has very low intensity in the tails. The main thrust of the program is aimed at producing in situ high-pressure high-temperature X-ray diffraction data, but other modes of operation, such as X-ray imaging have been accomplished. Technical details of the experimental setup will be presented along with initial results. 2013-05-16T08:10:58.054Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25598 High-pressure x-ray diffraction of (Mg0.80 Fe0.20)O at room temperature reveals a discontinuity in the bulk modulus at 40 (±5) GPa, similar to the pressure at which an electronic spin-pairing transition of Fe2+ is observed by Mössbauer spectroscopy. We determine the zero-pressure bulk modulus of low-spin magnesiowüstite to be between K70=136 and 246 GPa, with a pressure derivative (∂&∂P)70 between 5.2 and 3.9. The best fit unit-cell volume at zero pressure, V0=71 (±5) Å, is consistent with past estimates of the ionic radius of octahedrally-coordinated low-spin Fe2+ in oxides. A spin transition at lower-mantle depths between 1100 and 1900 km (40-80 GPa) would cause a unit-cell volume decrease (ΔV) of 3.7 (±0.5) to 2.0 (±0.1) percent and bulk sound velocity increase (Avø) of 7.6 (±4) percent at 40 GPa and 7.6 (±1.2) percent at 80 GPa. Even in the absence of a visible seismic discontinuity, we expect the spin transition of iron to imply correction to current compositional models of the lower mantle, with up to 10 mol percent increase of magnesiowüstite being required to match the seismological data. 2013-05-16T08:10:51.987Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25599 A tensonometer for stretching metal foils has been constructed for the study of strain broadening in X-ray diffraction line profiles. This device, which is designed for use on powder diffractometers and was tested on Station 2.3 at Daresbury Laboratory, allows in situ measurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on an 18 μm-thick copper foil experiencing strain levels of up to 5% using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental-parameters approach using the TOPAS peak-fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile predetermined using high-quality LaB6 reference powder. The deconvolution process yielded 'pure' sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from f.c.c. a/2〈110〉{111} dislocations, the variation of mechanical property with strain has been extracted. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities. 2013-05-16T08:10:48.661Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25603 The effects of pressure on the OH stretching frequencies of natural talc and two samples of synthetic 10-Å phase have been measured using a diamond-anvil cell and a synchrotron infrared source. The 10-Å phase was synthesized at 6.0-6.5 GPa, 600 °C for 46 hours (sample 10Å-46) and 160 hours (10Å-160). Spectra were collected up to 9.0 GPa (talc), 9.9 GPa (10Å-46), and 9.6 GPa (10Å-160). The OH stretching vibration of Mg ₃OH groups in talc occurs at 3677 cm⁻¹ at ambient pressure, and increases linearly with pressure at 0.97(2) cm⁻¹ GPa⁻¹. The same vibration occurs in 10-Å phase, but shows negligible pressure shift up to 2 GPa, above which the frequency increases linearly to the maximum pressure studied, at a rate of 0.96(3) cm⁻¹ GPa⁻¹ (10Å-46) and 0.87(3) cm⁻¹ GPa⁻¹ (10Å-160). Two other prominent bands in the 10-Å phase spectrum are suggested to be due to stretching of interlayer H₂O, hydrogen-bonded to the nearest tetrahedral sheet. These bands also show little change over the first 2 GPa of compression, as most of the compression of the structure is taken up by closing non-hydrogen bonded gaps between interlayer H₂O and tetrahedral sheets. Between 2 and 4 GPa, changes in band intensities suggest a rearrangement of the interlayer H₂O. 2013-05-16T08:10:36.773Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25608 A high pressure diffraction study, from ambient to 50 GPa, has been carried out on nanocrystalline TiN/amorphous BN nanocomposite materials prepared by plasma chemical vapor deposition. The compressibilities of these materials were found not to be significantly different from TiN. A large amount of biaxial and isotropic strain was found to build up on pressurization which continued to exist after depressurization and annealing indicating a permanent deformation under high pressure. This permanent deformation is located in the grain boundaries and is reduced by the presence of amorphous BN. 2013-05-16T08:10:19.733Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25609 The multi-anvil high-pressure facility on beamline 16.4 of the Synchrotron Radiation Source at Daresbury Laboratory has been upgraded from energy-dispersive diffraction operation to easily interchangeable energy-dispersive and angle-dispersive operation by the addition of a Laue-Bragg monochromator and an imaging plate detector. Details of the Laue-Bragg monochromator and endstation configuration are given. The performance of the end station is illustrated with data collected as part of a high temperature-pressure study of lawsonite. 2013-05-16T08:10:14.970Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25498 Synchrotron diffraction experiments with in situ laser heated diamond anvil cells and multi-anvil press synthesis experiments have been performed in order to investigate the reaction of scandium and carbon from the elements at high-(P,T) conditions. It is shown that the reaction is very sensitive to the presence of oxygen. In an oxygen-rich environment the most stable phase is ScOxCy, where for these experiments x=0.39 and y=0.50-0.56. If only a small oxygen contamination is present, we have observed the formation of Sc₃C₄, Sc₄C₃ and a new orthorhombic ScCx phase. All the phases formed at high pressures and temperatures are quenchable. Experimentally determined elastic properties of the scandium carbides are compared to values obtained by density functional theory based calculations. 2013-05-15T14:23:19.816Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25499 The melting curve of FeSi has been determined to 150 GPa in the laser-heated diamond anvil cell (LH-DAC) on the basis of discontinuities in the power versus temperature function. A multianvil experimental cross-check at 12 GPa using textural criteria as a proxy for melting is in good agreement with our LH-DAC results. The melting point of FeSi reaches ∼4000 K at the core mantle boundary and an extrapolated value of 4900 K at the inner-core boundary (ICB). We also present the melting curve as determined by the Lindemann melting law; this agrees well with our experimental curve to 70 GPa and then diverges to higher temperatures, reaching 6200 K at the ICB. These temperatures are substantially higher than previous LH-DAC determinations. The boundary of the ε-FeSi → CsCl-FeSi subsolidus transition has also been determined by synchrotron-based X-ray diffraction at high pressures, and the results confirm a negative Clapeyron slope for the transition. We conclude that if present, FeSi is likely to be solid within the D″ layer and is unlikely to be present within the inner core for any plausible bulk core silicon content. 2013-05-15T14:23:14.108Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25502 The crystal structures of eight tetragonal, gillespite-structured phases in the effenbergerite(BaₓCuSi₄O₁₀)-wesselsite (SrCuSi₄O₁₀) solid solution (Sr₁₋ₓBaₓCuSi₄O₁₀, where x is the mol fraction of the Ba end-member), have been refined from powder, netron time-of-flight, diffraction data. The accommodation of the larger, more electropositive Ba²⁺ cation within the crystal structure of SrCuSi₄O₁₀ is achieved by increasing the magnitude of the rotation of the square-planar CuO₄ group about the c axis, coupled with an anti-phase rotation, and concomitant tilting, of the Si₄O₁₀ polyhedral unit. To an excellent approximation, these structural changes are equivalent to a rigid sphere substitution, the radius of which is given by the compositionally averaged ionic radii of Sr²⁺ and Ba²⁺. The compositional-dependence of the lattice parameter c is significantly larger than that for a at low values of x, and is particularly well parameterised in terms of the variations of the calculated ionic radius of the alkaline-earth site and the observed tilt of the SiO₄ tetrahedron. The lattice parameter a exhibits a negative deviation from Vegard's rule resulting from the more complex, coupled structural response to the change in the effective ionic radius at the Sr/Ba site. 2013-05-15T14:23:10.525Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25504 The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 °C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na. 2013-05-15T14:23:07.106Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25503 High-pressure Brillouin spectroscopy of polycrystalline argon, measured using two scattering angles (180° and 70°), determines the isotropic elastic moduli, shear strength, equation of state, and refractive index of face-centered-cubic argon from 1.3 to 30 GPa at room temperature. The index of refraction n=1.33-1.67 over this pressure range. An Eulerian finite-strain analysis (Birch-Murnaghan equation of state) yields an isothermal bulk modulus and pressure derivative KT =15.1 (±1.1) GPa and K′T =5.4 (±0.3) at 2 GPa. The resulting equation of state agrees well with previous x-ray diffraction measurements, illustrating the suitability of high-pressure Brillouin scattering for characterizing the elasticity and strength of polycrystalline materials. 2013-05-15T14:23:06.999Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25516 X-ray diffraction measurements and Raman spectroscopy at room temperature document the equation of state and the frequency shifts for Eg, T2g, and A1g vibrational modes of polycrystalline LaB6 under pressure. The data exhibit smooth pressure dependencies, yielding a zero-pressure isothermal bulk modulus K0T =164 (±2) GPa in good accord with independent ultrasonic measurements, and show no evidence of structural or electronic phase transitions up to at least 25 GPa. 2013-05-15T14:22:38.731Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25546 Background: Following CBRN incidents health care professionals will be required to care for critically ill patients within the warm zone, prior to decontamination, whilst wearing CBRN-PPE. The loss of fine-motor skills may adversely affect delivery of medical care. Methods: 64 clinicians were recruited to perform, intubation, LMA placement, insertion of an IV cannula and IO needle whilst wearing CBRN-PPE. A fractional factorial design was employed, in which each of the 64 clinicians had two attempts at performing each skill whilst wearing CBRN-PPE and once unsuited according to a pre-specified sequence. Analysis: The unsuited and suit data were analysed independently with the primary outcome being time taken to complete each skill whilst suited. Analysis was undertaken using STATA (V9.2). Results: Mean times differ considerably by skill (p < 0.001). Overall, times to completion on attempt 2 were shorter than attempt 1 (p = 0.045), though the reduction in time differed significantly by skill (p = 0.004). LMA placement was on average completed nearly 45 s faster than intubation, and IO cannulation was nearly 90 s faster than IV cannulation. Whilst suited, 8% of intubation and 12% of intra-venous cannulation attempts were unsuccessful. Previous familiarity with CBRN-PPE did not improve performance (p = 0.23). Professional groups differed significantly (p = 0.009) with anaesthetists performing all skills faster than the other clinicians. Conclusion: This study supports the concept of instigating airway and vascular access skills whilst wearing CBRN-PPE but challenges the sole reliance on 'high-dexterity skills'. Intubation is feasible but must be considered within the context of the incident as the LMA may offer a viable alternative. Intra-venous access prior to casualty decontamination is arguably a pointless skill and should be replaced with IO access. 2013-05-15T14:21:37.878Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25549 The formation of a hexagonal rhenium carbide phase, Re₂C, from the elements has been studied in a laser heated diamond anvil cell in a P, V range of 20-40 GPa and 1000-2000 K. No indication for the existence of cubic rhenium carbide, as suggested in the literature, or any other phase was found and Re₂C is the only phase formed in the Re-C system up to around 70 GPa and 4000 K. A fit of a 3rd-order Birch-Murnaghan equation of state to the Re₂C P, V-data results in a bulk modulus of B₀ = 405 (30) GPa (B' = 4.6). The linear compressibility of Re₂C along [0 0 1] (∼ 500 GPa) is significantly larger than the compressibility in the (0 0 1) plane (∼ 360 GPa ∥[100]). Based on the observations for Re₂C, we predict the structure and elastic properties of an analogous Os₂C phase which is at least in the athermal limit more stable than any other osmium carbide studied previously by density functional theory based calculations. 2013-05-15T14:21:30.039Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25551 We determined high-pressure melting curves for Fe₃C, Fe₇C₃ and the Fe-Fe₃C eutectic using laser-heated diamond anvil cell techniques. The principal criterion for melting is the observation of plateaus in the temperature vs. laser power function, which is an expected behavior at isobaric invariant points (e.g. congruent, eutectic, or peritectic melting) as increased power provides the latent heat of melting. We verified this technique by reproducing the melting curves of well-studied congruently melting compounds at high pressure (Fe, Pt, FeS, Pb), and by comparison with melting determinations made using thermocouple-based large-volume press techniques. The incongruent melting curve of Fe₃C measured to 70 GPa has an apparent change in slope at ~ 8 GPa, which we attribute to stabilization of FeC₃ at the solidus and the creation of a P-T invariant point. We observe that Fe₇C₃ melts at higher temperatures than Fe₃C between 14 and 52 GPa and has a steep P-T slope, and on this basis predicts an expanding field of Fe₇C₃ + liquid with pressure. The Fe-Fe₃C eutectic melting curve measured to 70 GPa agrees closely with multi-anvil data and thermodynamic calculations. We also measured the eutectic composition as a function of pressure using an in situ X-radiographic imaging technique, and find a rapid drop in carbon in the eutectic composition above about 20 GPa, generally consistent with previous thermodynamic calculations, and predict that the eutectic lies close to pure iron by ~ 50 GPa. We use these observations to extrapolate phase relations to core-relevant pressures. Convergence of the Fe₃C and Fe-Fe₃C eutectic melting curves indicate that Fe₃C is replaced at the solidus by Fe₇C₃ at ~ 120 GPa, forming another P-T invariant point and a new eutectic between Fe and Fe₇C₃. Thus, Fe₃C is unlikely to be an important crystallizing phase at core conditions, whereas Fe₇C₃ could become an important crystallizing phase. 2013-05-15T14:21:21.948Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25558 The formation of cubic TiCₓfrom the elements was studied in a laser-heated diamond anvil cell at pressures up to 26 GPa. Annealed samples at these pressures show no splitting of the cubic (1 1 1) or (2 2 2) reflection. This is in contrast to an earlier study, in which a splitting of the (1 1 1) reflection was observed above 18 GPa. The recovered sample had a lattice parameter of 4.3238(6) Å, which implies that the synthesis gave fully stoichiometric TiC. Density functional theory-based model calculations were used to study the dependence of the total energy of a rhombohedral distortion. In these model calculations the total energy was minimal for the undistorted (cubic) lattice. Therefore, the results obtained here imply that at least for titanium carbides with a high carbon content no pressure-induced structural phase transition up to at least 26 GPa occurs. The appearance of a trigonal TiCₓ polymorph during the synthesis is discussed in terms of its relative stability with respect to the cubic phase. 2013-05-15T14:21:07.236Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25569 The development of monodisperse crystalline particles in cordierite glass doped with Cr³⁺ after a two-step heat treatment is elucidated by a combination of time-resolved small and wide angle x-ray scattering (SAXS/WAXS) experiments with electron microscopy. The effects of bulk and surface crystallization can clearly be distinguished, and the crystallization kinetics of the bulk phase is characterized. The internal pressure due to structural differences between the crystalline and amorphous phase is measured but the physical cause of this pressure can not unambiguously be attributed. The combined measurements comprise a nearly full characterization of the crystallization processes and the resulting sample morphology. 2013-05-15T14:20:40.364Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25572 Characterizing the nature of medium-range order (MRO) in liquids and disordered solids is important for understanding their structure and transport properties. However, accurately portraying MRO, as manifested by the first sharp diffraction peak (FSDP) in neutron and X-ray scattering measurements, has remained elusive for more than 80 years. Here, using X-ray diffraction of amorphous red phosphorus compressed to 6.30 GPa, supplemented with micro-Raman scattering studies, we build three-dimensional structural models consistent with the diffraction data. We discover that the pressure dependence of the FSDP intensity and line position can be quantitatively accounted for by a characteristic void distribution function, defined in terms of average void size, void spacing and void density. This work provides a template to unambiguously interpret atomic and void-space MRO across a broad range of technologically promising network-forming materials. 2013-05-15T14:20:36.524Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25574 High-resolution angular-dispersive x-ray diffraction shows that the intermetallic compound AuIn₂ retains its initial CaF₂ structure to pressures of 23 GPa. We observe continuous broadening of diffraction lines with pressure, leading to amorphization at 24 GPa. The pressure-volume equation of state exhibits an anomaly around 2.7 GPa, in agreement with previous findings and not attributable to nonhydrostaticity. Instead, ab initio plane-wave self-consistent field calculations indicate that the observed anomaly is associated with topological changes in the electronic band structure under pressure. 2013-05-15T14:20:32.622Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25582 An apparatus for measuring the complex impedance of samples with high impedances is described. Complex impedance spectra were collected from a range of borosilicate glasses of composition (B₂O₃)₄(Li₂O)(LiBr)ₓ(NaBr)₁₋ₓ at pressures and temperatures ranging from 1 to 5 GPa and 350 to 450 °C, respectively. These data were used to determine AC conductivities and activation energies in order to test the Modified Random Network model of glass structure. Our results are in line with the predictions of this theory. 2013-05-15T14:20:06.410Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25563 Low-divergence synchrotron-sourced X-rays enable a radiographic imaging scheme for full characterization of binary chemical reactions and characterization by type of more complex reactions, in situ, in diamond anvil cells (DAC). Spatially resolved reactants are induced to react by laser heating of their interface. The spatially intermediate products are observed through X-ray absorption contrast. Limits to the technique include the ability to maintain controlled experiment geometry during compression and the ability to resolve chemical differences between reactants and products by X-ray absorption. The ability to make in situ observations at experimental pressure and temperature obviates the problem with quenching techniques for capturing liquid compositions in experiments with dimensions smaller than the diffusion length during quenching time. Partially molten Fe-alloy systems, of poor quenchability, are examined at DAC pressures and temperatures for relevance to Earth's core constitution and evolution. Determinations of eutectic melting in Fe-FeS match known results. Of the probable light elements that may alloy with Fe in the Earth's liquid outer core, Fe-FeS experiments show only modest quenching problems, but C and Si alloy experiments are highly vulnerable to quenching artifacts. The observed reactivity of FeS, Fe₃C, FeSi, and FeO(OH) with Fe in DAC makes the observed non-reactivity between Fe and FeO more significant, reducing the probability that oxygen alone is the major alloy in Earth's molten outer core. 2013-05-15T04:00:12.426Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25561 We studied the compressibility of monolithic fully dense electrodeposited nanocrystalline Ni (∼29 nm grain size) under both quasihydrostatic and nonhydrostatic conditions up to a nominal pressure of 50 GPa using angle-dispersive x-ray diffraction. We obtained an equation of state consistently and unambiguously from each measured reflection. The apparent bulk modulus measured under nonhydrostatic conditions is larger than that of the corresponding coarse-grained material under either type of compression, but is nearly the same when measured under quasihydrostatic conditions. These results may be consistent with a strength, but not necessarily a bulk modulus, that is enhanced in the nanomaterial relative to its coarse-grained counterparts. 2013-05-15T02:50:09.801Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25515 We present isothermal volume compression behavior of two polycrystalline (Mg,Fe)O samples with FeO = 39 and 78 mol% up to ~90 GPa at 300 K using synchrotron X-ray diffraction and neon as a pressure-transmitting medium. For the iron-rich (Mg₀․₂₂Fe₀․₇₈)O sample, a structural transition from the B1 structure to a rhombohedral structure was observed at 41.6 GPa, with no further indication of changes in structural or compression behavior changes up to 93 GPa. In contrast, a change in the compression behavior of (Mg₀․₆₁Fe₀․₃₉)O was observed during compression at P ≥ 71 GPa and is indicative of a spin crossover occurring in the Fe²⁺ component of (Mg₀․₆₁Fe₀․₃)O. The low-spin state exhibited a volume collapse of ~3.5%, which is a larger value than what was observed for a similar composition in a laser-heated NaCl medium. Upon decompression, the volume of the high-spin state was recovered at approximately 65 GPa. We therefore bracket the spin crossover at 65 ≤P (GPa) ≤77 at 300 K (Mg₀․₆₁Fe₀․₃)O. We observed no deviation from the B1 structure in (Mg₀․₆₁Fe₀․₃)O throughout the pressure range investigated. 2013-05-13T00:20:12.296Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25415 7 page(s) 2013-05-09T09:35:35.012Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25425 The 10-Å phase (TAP) is a hydrous magnesium silicate that forms from the reaction of talc with H₂O at high pressures. Its high-pressure, low-temperature stability means that it could be a storage site for H₂O in subduction zones. We have determined the position of the TAP dehydration reaction, TAP = enstatite + coesite + H₂O, in phase-equilibrium experiments from 5.0 to 7.1 GPa. Because previous studies had suggested that the composition of TAP is a function of synthesis duration, we used a TAP sample that was synthesised for 392 h. Over the pressure interval of our experiments, the dehydration reaction is isothermal, occurring at a temperature of ~690°C. It is coincident, within experimental uncertainty, with the position of the dehydration reaction of TAP synthesised in short experiments (up to 46 h). Above 7.5 GPa, TAP breaks down to enstatite+stishovite +H₂O. This reaction has a negative dP/dT and terminates at an invariant point involving the 3.65-Å phase at ~9.5 GPa,500°C. The zero volume change implied by the isothermal reaction TAP=enstatite+coesite+H₂O was used to calculate the interlayer H₂O content of TAP along the reaction. A best-fit H₂O content of 1 H₂O pfu was obtained. This H₂O content is independent of TAP synthesis conditions, suggesting that variations in previously measured H₂O contents of TAP occur during quenching and decompression of the samples. The stability of TAP in the Earth is probably limited to cold subduction zones, but in these, it could persist to 300 km depth. 2013-05-09T09:35:13.565Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25431 Crystalline zeolitic materials, such as hydroxycancrinite, hydroxysodalite, herschelite and nepheline, are often synthesized from geopolymerization using fly-ash and solutions of NaOH at high temperatures. Comprised mainly of 6-membered aluminosilicate rings that act as basic building units, their crystal structures may provide insight into the reaction products formed in NaOH-activated fly ash-based geopolymers. Recent research indicates that the hydroxycancrinite and hydroxysodalite may play an important role as possible analogues of zeolitic precursor in geopolymers. Herein is reported a high pressure synchrotron study of the behavior of hydroxycancrinite exposed to pressures up to 6.1 GPa in order to obtain its bulk modulus. A refined equation of state for hydroxycancrinite yielded a bulk modulus of Ko = 46 ± 5 GPa (assuming Ko′ = 4.0) for a broad range of applied pressure. When low pressure values are excluded from the fit and only the range of 2.5 and 6.1 GPa is considered, the bulk modulus of hydroxycancrinite was found to be Ko = 46.9 ± 0.9 GPa (Ko′ = 4.0 ± 0.4, calculated). Comparison with the literature shows that all zeolitic materials possessing single 6-membered rings (i.e., hydroxycancrinite, sodalite and nepheline) have similar bulk moduli. 2013-05-09T09:35:09.028Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25432 The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous GeTe-Sb₂Te₄(GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. 2013-05-09T09:35:08.268Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25437 Structural studies of the ferrimagnetic (TN = 200 K) Mott insulator GaFeO₃ (SG Pc2₁n) to 70 GPa, complemented by ⁵⁷Fe Mössbauer spectroscopy and resistance (R) measurements at compression, decompression, and recompression, reveal a fascinating sequence of structures. Starting at ∼25 GPa a new structure, an orthorhombic perovskite (Pv) (SG Pbnm), is sluggishly formed followed by a volume V(P) drop of 5.4%. The complete formation of the Pv occurs at 42 GPa. In the 0-33 GPa range TN reaches 300 K and R(P) decreases by one order of magnitude. At 53 GPa an isostructural transition is detected, characterized by a discontinuous drop of V(P) by ∼3%. Mössbauer spectra (MS) reveal a nonmagnetic component coexisting with the magnetic one at ∼60 GPa. Its abundance increases and above 77 GPa no sign of a magnetic hyperfine interaction is detected down to 5 K. Concurrently, one observes a continuous yet precipitous decrease in R(P) taking place in the 53-68 GPa range, leading to an onset of the metallic state at P = 68 GPa. These electronic/magnetic features of the high pressure (HP) Pv are consistent with a Mott transition. With pressure decrease below 50 GPa, the insulating Pv is recovered, and at ∼24 GPa a 1st-order structural transition takes place to a LiNbO3-type structure with SG R3c. This structure remains stable down to ambient pressure and with recompression it is stable up to 50 GPa, afterwards it transforms back to the HP Pv structure. It is noteworthy that this transition occurs at the same pressure, regardless of the preceding structures: Pbnm or R3c. The results are compared with hematite (Fe₂O₃, SG R3̄c) and other ferric oxides. The mechanisms of the transitions are discussed. 2013-05-09T09:34:53.832Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25441 The pressure and temperature dependent fluorescence line-shift of strontium tetraborate has been measured concurrently with x-ray diffraction from the pressure standards sodium chloride or gold. Temperature was found to have a small effect on the fluorescence line-shift under pressure. We found a maximum pressure uncertainty of ±1.8 GPa at 25 GPa (7.2%) and 857 K when making no temperature correction. The fluorescence line-shifts for ruby, Alexandrite, and samarium-doped yttrium aluminum garnet were also determined, using our strontium tetraborate calibration to determine pressure and a thermocouple to measure temperature. Fluorescence measurements were extended up to 800 K for ruby and Alexandrite. Temperature was found to have a small effect on the fluorescence line-shift of samarium-doped yittrium aluminum garnet. We found a maximum uncertainty of ±2.7 GPa at 25 GPa (11.1%) and 857 K when no temperature correction was applied. We determined equations relating to the fluorescence line position from these data, which include a cross derivative term to account for the combined effect of pressure and temperature. We present a method to independently determine pressure and/or temperature from combined fluorescence line-shift measurements of a pair of optical sensors. 2013-05-09T09:34:45.273Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25446 The crystalline, liquid and amorphous phase stabilities and transformations of the Ge₁Sb₂Te₄ (GST124) alloy are investigated as a function of pressure and temperature using synchrotron diffraction experiments in a diamond anvil cell. The results indicate that the solid-state amorphization of the cubic GST124 phase under high pressure may correspond to a metastable extension of the stability field of the GST124 liquid along a hexagonal crystal-liquid phase boundary with a negative P-T slope. The internal pressures generated during phase change are shown to be too small to affect phase stability. However, they may be important in understanding reliability issues related to thermomechanical stress development in phase change random access memory structures. 2013-05-09T09:34:37.559Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25450 The compressibilities of two AFm phases (strätlingite and calcium hemicarboaluminate hydrate) and hydrogarnet were obtained up to 5 GPa by using synchrotron high-pressure X-ray powder diffraction with a diamond anvil cell. The AFm phases show abrupt volume contraction regardless of the molecular size of the pressure-transmitting media. This volume discontinuity could be associated to a structural transition or to the movement of the weakly bound interlayer water molecules in the AFm structure. The experimental results seem to indicate that the pressure-induced dehydration is the dominant mechanism especially with hygroscopic pressure medium. The Birch-Murnaghan equation of state was used to compute the bulk modulus of the minerals. Due to the discontinuity in the pressure-volume diagram, a two stage bulk modulus of each AFm phase was calculated. The abnormal volume compressibility for the AFm phases caused a significant change to their bulk modulus. The reliability of this experiment is verified by comparing the bulk modulus of hydrogarnet with previous studies. 2013-05-09T09:34:23.180Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25454 Synthetic basic sodalite, Na₈[AlSiO₄]₆(OH)₂·2H₂O, cubic, P43n, (also known as hydroxysodalite hydrate) was prepared by the alkaline activation of amorphous aluminosilicate glass, obtained from the phase separation of Class F fly ash. The sample was subjected to a process similar to geopolymerization, using high concentrations of a NaOH solution at 90 °C for 24 hours. Basic sodalite was chosen as a representative analogue of the zeolite precursor existing in Na-based Class F fly ash geopolymers. To determine its bulk modulus, high-pressure synchrotron X-ray powder diffraction was applied using a diamond anvil cell (DAC) up to a pressure of 4.5 GPa. A curve-fit with a truncated third-order Birch-Murnaghan equation of state with a fixed K'o = 4 to pressure-normalized volume data yielded the isothermal bulk modulus, Ko = 43 ± 4 GPa, indicating that basic sodalite is more compressible than sodalite, possibly due to a difference in interactions between the framework host and the guest molecules. 2013-05-09T09:34:06.448Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25458 This study examines the influence of Al substitution for Si on the bulk modulus of calcium silicate hydrate I [C-S-H(I)], a structural analogue of C-S-H, by performing high-pressure synchrotron X-ray diffraction experiments in two C-S-H(I) samples: one a hydration product of alkali-activated slag and the other a synthetic C-S-H(I). The test result shows that not only the bulk modulus but also the incompressibility of the lattice parameters a, b, and c of two C-S-H(I) samples are very similar to each other, regardless of the Al substitution. This result may be due to the four-coordinated configuration of the substituted Al, which makes the dreierketten silicate chains maintain the same arrangement after the substitution. 2013-05-09T09:33:53.056Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25467 In situ synchrotron X-ray diffraction was used to observe the reaction induced by laser heating of a mixture of tantalum and boron in a diamond anvil cell. Laser heating at pressures of 12 and 24 GPa resulted in the formation of TaB₂. The bulk modulus of TaB₂ (B₀ = 341(7) GPa) was determined from a fit of a second-order Birch-Murnaghan equation of state to the p-V data. Density functional theory based calculations complemented the experimental observations and were used to obtain the full tensor of elastic stiffness coefficients. The choice of the most appropriate exchange-correlation functional for the description of elastic properties is discussed. 2013-05-09T09:33:06.488Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25468 The objective of this study was to assess the impact of chemical, biological, radiological, nuclear personal protective equipment (CBRN-PPE) on the ability to secure an endotracheal tube (ETT) with either the Thomas Tube Holder™ or cotton tape tied in a knot. Seventy-five clinicians secured an ETT in a previously intubated manikin with the Thomas Tube Holder™ and cotton tape. A mixed quantitative and qualitative research design was used to gauge actual performance times and perceptions of difficulties. Following completion of the study, 25 clinicians were interviewed to gauge their experiences of securing the ETT with both devices while wearing CBRN-PPE. The mean time to apply the Thomas Tube Holder was 29.02 seconds, compared with tape which took a mean of 58 seconds (p=0.001). Clinicians rated the Thomas Tube Holder as easier to use than tape (Mann-Whitney z=9.934; p<0.001), which was confirmed during interviews. Of the clinicians interviewed, 92% perceived that the Thomas Tube Holder provided the better method for securing an ETT, none of the clinicians identified the tape as the best method for securing the endotracheal tube while wearing CBRN-PPE. Clinicians identified that the design of the Thomas Tube Holder facilitated the gross motor movement required for application. The Thomas Tube Holder is easier and faster to apply when wearing CBRN-PPE when compared with cotton, and the Thomas Tube Holder is perceived by the participants as being more effective at preventing accidential extubation. 2013-05-09T09:33:02.789Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25472 The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The α phase was found to transform into the α′ phase at 0.87±0.04 GPa with a volume change in 0.1±0.3 cc/mol. A fit of a second-order Birch-Murnaghan equation to the data gave Vₒ =16.94±0.08 cc/mol and Kₒ =6.7±0.5 GPa for the α phase and Vₒ =16.4±0.1 cc/mol and Kₒ =9.1±0.3 GPa for the α′ phase. The α′ phase was found to transform to the A17 phase of black phosphorus at 2.68±0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second-order Birch-Murnaghan equation to our data combined with previous measurements gave Vₒ =11.43±0.05 cc/mol and Kₒ =34.7±0.5 GPa for the A17 phase, Vo =9.62±0.01 cc/mol and Ko =65.0±0.6 GPa for the A7 phase and, Vₒ =9.23±0.01 cc/mol and Kₒ =72.5±0.3 GPa for the simple cubic phase. 2013-05-09T09:32:49.450Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25475 X-ray diffraction from LaB₆ standards document a precision of 478 ppm in lattice-parameter determinations for beamline 12.2.2 at Lawrence Berkeley National Laboratory′s Advanced Light Source, a facility for characterizing materials at high pressures and temperatures using laser- and resistance-heated diamond cells. Melting of Ni, Mo, Pt and W, resistively heated at 1 atm pressure in Ar, provides a validation of the beamline spectroradiometric system that is used to determine sample temperatures. The known melting temperatures, which range from 1665 to 3860 K for these metals, are all reproduced to within ±80 K. 2013-05-09T09:32:07.160Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25477 We have measured the equation of state of the intermetallic compound AuIn₂ up to 20 GPa and Cd₀․₈Hg₀․₂ up to 50 GPa using methanolethanolwater solution or argon as pressure media. In the experiments performed with argon as pressure medium, we minimized non-hydrostatic conditions by thermally annealing the sample. We present data revealing compressibility anomalies in AuIn₂ at 2.7 GPa and in Cd₀․₈Hg₀․₂ near 8, 18 and 34 GPa with methanolethanolwater and argon. At pressures above 5 GPa the PV data for AuIn₂ and Cd₀․₈Hg₀․₂ from experiments preformed with argon as a pressure medium start deviating from those using methanolethanolwater, and the equation of state based on experiments in argon is stiffer compared with that in methanolethanolwater. This behavior is consistent with the relative merits of the two pressure transmitting media as documented in the literature. We also provide a brief summary of the results of electronic structure calculations that associate these anomalies with electronic topological transitions. 2013-05-09T09:31:55.799Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25487 8 page(s) 2013-05-09T09:31:08.985Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25492 High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of osmium to over 60 GPa at room temperature. We find the zero-pressure bulk modulus in fair agreement with other experiments as well as with relativistic electronic band-structure calculations: Osmium is the densest but not the most incompressible element at ambient conditions. We also find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of osmium as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations but disagrees with recent claims that the electronic structure and equation of state of osmium exhibit anomalies at pressures of ∼15-25 GPa; the discrepancies are may be due to the effects of texturing. 2013-05-09T05:00:11.768Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25484 Earlier measurements of elastic moduli of nc-TiN/a-Si₃N₄ nanocomposites of different composition and hardness by means of vibrating reed and surface Brillouing scattering, that yield Young's and shear modulus, as well as the Poisson's ratio, have been confirmed by high-pressure X-ray diffraction measurements, that yield bulk modulus. It is found that elastic moduli of all measured samples are essentially the same within relatively small error of measurements, and only slightly lower than that of pure TiN. The nanocomposites are superhard thanks to their unique nanostructure with strengthened SiNx interface. 2013-05-09T01:50:18.790Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25290 The lithosphere-asthenosphere boundary (LAB) is a fundamental element of the dynamic Earth system. While various geophysical methods can provide useful proxies for imaging the LAB, including seismic studies (surface-wave inversion, receiver-function analysis, and investigation of seismic anisotropy) and magnetotelluric methods, consistent interpretations of these results remain elusive. Here, we are developing a systematic, comprehensive and realistic suite of synthetic data with the aim of benchmarking various seismological methods for imaging the LAB. Our study is based on a hypothetical regional geological model (800X800X400km) that is smoothly embedded within a standard global Earth model. The regional model extends from oceanic to thick cratonic lithosphere. Physical proper ties of the regional model (i.e. anisotropic elastic moduli, density, thermal and rheological parameters) match prescribed surface heat-flow and geoid boundary conditions and are computed using an approach based on thermodynamics, mineral physics, geochemistry, petrology, and solid-Earth geophysics. Anisotropy is incorporated into the model through both mantle-flow calculations and prescribed fossil anisotropy within cratonic lithosphere. Long-period synthetic seismograms are computed forteleseismic events using SPECFEM3DGLOBE, which provides full wave-equation modeling of seismic wave propagation incorporating phenomena such as anisotropy, attenuation and fluid-solid interfaces. To ensure a realistic (non-ideal) azimuthal distribution, the event locations are based on a subset of a one-year global catalog within the magnitude range from 6.0 to 7.0. Forward modeling of magnetotelluric response will also be under taken. The data from this study will be released as a benchmark dataset fortesting by research groups. 2013-04-24T04:52:06.344Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25293 The Lawn Hill Impact Structure is situated approximately 240km NNW of Mt Isa in north eastern Queensland, and consists of a ring of low Cambrian limestone hills overlying very weakly metamorphosed Proterozoic shales and other sediments. The world class Century Pb/Zn deposit sits at the margin of the structure and is hosted within the Proterozoic basement. The deposit exhibits strong indications of impact related brecciation previously attributed to other causes, or left unexplained. These include a variety of breccia textures, some incorporating the much younger Cambrian limestone, and ranging from micro to mega scale, including a one million tonne "megaclast" of Century-like ore encapsulated with Cambrian limestone adjacent to the main deposit. Other interpreted impact effects include milled limestone "breccia dykes" injected deep into the deposit and impact related hydrothermal remobilisation of ore minerals with small galena deposits observed within the Cambrian limestone. These were possibly formed through a process similar to Mississippi Valley Type Pb/Zn deposits. Additional results from a fluid inclusion study indicate that temperatures and fluid composition were within tolerances for remobilisation of Pb and Zn during impact-related fluid flow; however, sealing of flow paths and short lived convection may limit the size of possible impact-generated ore deposits. New constraints are placed on the age of the impact structure through 40 Ar/39 Ar dating of impact melt from the central uplift. 2013-04-24T04:51:53.781Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25285 A worldwide database of over 16,000 combined U-Pb and Hf-isotope analyses of zircon, largely from detrital sources, has made it feasible to examine processes of crustal evolution on a global scale, and to test existing models for the growth of continental crust through time. Understanding the growth rate of the continental crust is critical in evaluating the proportion of juvenile material added to the crust at each point during its evolution. The amount of juvenile material produced at any given time is commonly underestimated, because some of that material was later reworked, and the record of the original juvenile material is buried or lost during subsequent crustal evolution. The approach proposed in this study attempts to account forthis effect, and "restore" an indication of the true juvenile input using the integrated dataset. The age data alone would support an Episodic Growth model, but the Hf-isotope data reveal that most of the magmatic rocks represented in the major "episodes" were derived by the reworking of pre-existing crust, especially after ca 2.5 Ga; the juvenile contribution represents a small proportion of most magmatic episodes. Modelling of the ages of the recycled components emphasises the repeated reworking of Archean components, supporting an Early Growth model. Furthermore, the large Hf-isotope datasets allow the definition of different patterns of continental crust generation in different tectonic settings, thus providing a basis for unraveling the global geodynamic evolution and supercontinent cycles of the ancient Earth. 2013-04-22T20:10:23.759Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25257 The Fonualei Spreading Centre is a nascent series of en echelon ridges that extend north from near Fonualei volcano, on the Tonga arc front, to the Mangatolu Triple Junction in the northeastern Lau Basin. Fresh basaltic glasses dredged from these ridges afford an excellent opportunity to evaluate geochemical changes with increasing depth to the slab. Here we augment previously published major and trace element data with new Sr, Nd, Pb, Hf and U-Th-Ra isotope data for selected Fonualei Spreading Centre samples as well as present new Hf isotope data from boninites and seamounts to the north of Tonga. The Pb and Hf isotope data are used to appraise interpretations of the extent and distribution of Samoan plume mantle beneath the Lau Basin based on He and Pb isotope data. If elevated ²⁰⁸Pb and lowered Hf isotope ratios in lavas from Niuafo'ou Island and the Mangatolu Triple Junction reflect a Samoan plume influence this is not visible in He isotopes. The boninite and seamount data indicate that the tear in the northern end of the slab may not extend east as far as the boninite locality. Mantle flow is inferred to be oriented to the southwest. In the Fonualei Spreading Centre lavas, Ce/Pb, ⁸⁷Sr/⁸⁶Sr and ²⁰⁸Pb/²⁰⁴Pb increase, whereas U/Th, Th/Nb and ¹⁴³Nd/¹⁴⁴Nd decrease, with increasing distance from the arc front. These changes are accompanied by increasing slab surface temperatures (725-940 degrees C) as inferred from decreasing H₂O/Ce ratios. Consistent with experimental data, the geochemical trends are interpreted to reflect changes in the amount and composition of wet pelite melts and aqueous fluids derived from the slab under appropriate conditions. With one exception, all of the lavas preserve both ²³⁸U excesses and ²²⁶Ra excesses. Ba-Yb, Na₈-Fe₈ and U-series isotope systematics suggest that lavas from the Fonualei Spreading Centre and Valu Fa Ridge reflect fluid-fluxed melting. However, there is a change to decompression melting in lavas from the East and Central Lau Spreading Centres where slab surface temperatures reach approximately 900-1000 degrees C. A similar observation is found for the Manus and East Scotia back-arc basins and may reflect the absence of lawsonite in the subducted basaltic crust. 2013-04-18T13:20:47.847Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25260 Recent and present volcanism in the Vanuatu arc (South West Pacific Ocean) occurs at a variety of volcano types that exhibit a wide range of eruptive behaviour: from post-caldera lava-lake activity and lava flows at shield volcanoes (Ambrym), moderately explosive sub-plinian events and associated pyroclastic-flows and lava flows at stratovolcanoes (Lopevi), to persistent strombolian and vulcanian-style eruptions at scoria cones (Yasur). This precludes a generic model of magmatic and eruptive behaviour for the Vantuatu arc volcanoes and necessitates a detailed study of each system. Uranium-series disequilibria in volcanic rocks offer unique insights into pre-eruptive magmatic systems over process-relevant timescales e.g., ²³⁸U-²³⁰Th (380 Ka), ²³⁰Th-²²⁶Ra (8 Ka) and ²²⁶Ra-²¹⁰Pb (100 a). The short half-life of ²¹⁰Pb (t½ = 22.6 years) and the volatile nature of the intermediate isotope, ²²²Rn, (intermediate between the ²²⁶Ra parent and ²¹⁰Pb daughter) provide valuable information on magma transport, evolution and degassing over a timescale more pertinent to the processes leading up to volcanic eruptions. We present new Uranium-series isotope data (U-Th-Ra-²¹⁰Pb) for young ( 1) in the most mafic samples suggesting that ²²²Rn gas accumulation and fluxing preceding and/or during eruption (on a decadal timescale) may be responsible for the more explosive-style of eruption witnessed at this volcano. Significant accumulation of recently crystallised plagioclase phenocrysts can also create ²¹⁰Pb excesses in volcanic rocks, however, this process is not supported by the petrographic and geochemical data. In summary ²¹⁰Pb-²²⁶Ra disequilibria in Vanuatu volcanic rocks reveal a strong link between pre-eruptive magma degassing systematics and the resultant style of volcanic activity. 2013-04-18T13:20:29.874Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25170 The high-pressure structures of nickel monosilicide (NiSi) have been investigated to 124 GPa by synchrotron-based X-ray powder diffraction studies of quenched samples from laser-heated diamond anvil cell experiments, and the equations of state of three of these phases have been determined at room temperature. NiSi transforms from the MnP (B31) structure (space group Pnma) to the ε-FeSi (B20) structure (space group P213) at 12.5 ± 4.5 GPa and 1550 ± 150 K. Upon further compression, the CsCl (B2) structure (space group Pm3m) becomes stable at 46 3 GPa and 1900 150 K. Thus, NiSi will be in the B2 structure throughout the majority of the Earths mantle and its entire core, and will likely form a solid solution with FeSi, which is already known to undergo a B20->B2 transition at high pressure. Data from the quenched (room-temperature) samples of all three phases have been fitted to the third-order Birch-Murnaghan equation of state. For the MnP (B31) structure this yields K₀ = 165 ± 3 GPa with K₀′ fixed at 4 and V₀ fixed at 12.1499 ų atom⁻¹ [V₀ from unpublished neutron diffraction measurements on the same batch of starting material; Wood (2011), personal communication]. For the ε-FeSi (B20) structure, K₀ =161 ± 3 GPa and K₀′ = 5.6 ± 0.2 with V₀ fixed at 11.4289 ų atom⁻¹. For the CsCl (B2) structure, K₀ = 200 ± 9 GPa, K₀′ = 4.6 ± 0.1 and V₀ = 11.09 0.05 ų atom⁻¹. The ambient volume of NiSi, therefore, decreases by 6% at the first phase transition and then by a further 3% at the transition to the CsCl structure. Traces of additional NiSi structures predicted by Vočadlo, Wood & Dobson [J. Appl. Cryst. (2012), 45, 186-196; part I], and labelled therein as Pbma-I, Pnma-II, and possibly also Pnma-III and P4/nmm, have been detected. 2013-04-11T11:21:48.240Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25043 12 page(s) 2013-04-08T13:29:40.246Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25077 Synchrotron X-ray diffraction data was collected from a sample of monocarboaluminate 3CaO•Al₂O₃•CaCO₃• 11H₂O from ambient pressure to 4.3 GPa. The refined crystal structure at ambient pressure is triclinic with parameters a = 5.77(2)Å, b = 8.47(5)Å, c = 9.93(4)Å, α = 64.6(2)°, β = 82.8(3)°, γ = 81.4(4)°, and space group of P1 or P1̄. It showed some degree of perfectly reversible pressure-induced dehydration with a non-hygroscopic pressure-transmitting medium. However the dehydration effect does not critically affect a bulk modulus due to its strong framework. The isothermal bulk modulus of monocarboaluminate was found to be 53(5) GPa and 54(4) GPa with 3rd order and 2nd order Birch-Murnaghan Equation of state, respectively. That value is higher than for any other reported AFm or AFt phase. The pressure-volume behavior of the monocarboaluminate was compared with that of previous studied hemicarboaluminate. 2013-04-08T13:28:35.824Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25092 1 page(s) 2013-04-08T13:27:22.966Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25093 1 page(s) 2013-04-08T13:25:06.577Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25101 Experiments at 20-97 GPa and 2000 K in the system CaO-MgO-TiO₂-SiO₂ constrain phase relations involving Mg-rich and Ca-rich perovskite solid solutions at conditions relevant to the Earth's deep Transition Zone and lower mantle. Bulk compositions were investigated with molar Ti/(Ti + Si) up to 0·5 within the quasi-ternary 'perovskite plane', which is defined by a reciprocal solution among the components MgSiO₃, MgTiO₃, CaSiO₃, and CaTiO₃. Multi-anvil experiments at 20 GPa and 2000 K on bulk compositions within the plane produce akimotoite coexisting with Ca-perovskites that lie close to the CaSiO₃-CaTiO₃ join. Higher-pressure experiments using a laser-heated diamond anvil cell constrain the position of a two-perovskite field that extends into the perovskite plane from the solvus along the MgSiO₃-CaSiO₃ binary join, where limited mutual solubility exists between MgSiO₃ and CaSiO₃ perovskites. On the join MgSiO₃-MgTiO₃, MgTiO₃ solubility in MgSiO₃ perovskite increases with pressure, with MgSi0·8Ti0·2O₃ perovskite stable at ∼50 GPa. Limited reciprocal solution at ∼25 GPa results in an expansive two-perovskite field that occupies much of the Si-rich portion of the perovskite plane. Solution of Ti into Mg-rich and Ca-rich perovskites enhances the solubility of reciprocal Ca and Mg components, respectively. Increase in pressure promotes reciprocal solution, and the two-phase field collapses rapidly with pressure toward the MgSiO₃-CaSiO₃ join. We find that a single-phase, orthorhombic perovskite with near equimolar Ca and Mg is stable in a composition with Ti/(Ti + Si) of only 0·05 at 97 GPa, requiring that by this pressure the two-phase field occupies a small area close to the MgSiO₃-CaSiO₃ join. On the basis of experiments at∼1500 K, temperature has only a mild effect on the position of the Ca-rich limb of the solvus. Ca(Ti,Si)O₃ mineral inclusions in deep sublithospheric diamonds could not have formed in equilibrium with Mg-perovskite owing to their virtual lack of MgSiO₃ component at pressures of Mg-perovskite stability, but may have equilibrated with Transition Zone MgSiO₃-rich phases at lower pressures; this observation can be extended generally to near-endmember CaSiO₃ inclusions. On an iron-free basis, the average bulk compositions of clinopyroxene-ilmenite and orthopyroxene-ilmenite megacrysts from kimberlites plot in single-perovskite fields at pressures greater than about 45 and 65 GPa, respectively, when projected onto the perovskite plane. We predict that the effect of iron will not be large, and estimate that single-phase perovskites may form at somewhat lower pressures than in the iron-free system. Thus, the origin of pyroxene-ilmenite megacrysts from single-phase perovskite solutions in the lower mantle is plausible on the basis of phase relations, although a lower pressure magmatic origin appears more likely. Deeply subducted Ti-rich lithologies such as ocean-island basalt will crystallize a single perovskite rather than a two-perovskite assemblage beginning at pressures of ∼80 GPa. Normal mid-ocean ridge basalt and primitive mantle peridotite are expected to remain within a two-phase perovskite field until Mg-perovskite transforms to post-perovskite. 2013-04-08T13:24:33.942Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24968 Due to the expanse and remoteness of Australian communities we require local exper ts and enthusiasts to provide support and share their knowledge with schools. The project involves an online education portal allowing access by students to earthquake recordings in their own and other schools. The data schools collect will be useful to researchers and could complement networks run by government and state agencies due to the high quality of the instruments and will be stored at internationally accessible and supported data management centres. A growing community of volunteers is forming to support the program within their local area. Over the duration of the project these volunteers will enhance the project through provision of technical exper tise as well as promotion within the education sector. 2013-03-28T02:22:53.384Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24980 The fractionated, megacrystic Wyangala Granite, of the Eastern Lachlan Fold Belt in central NSW provides an excellent natural laboratory for regional scale analysis of strain localisation. The granite forms irregular shaped areas of relatively undeformed granodiorite with large (10 cm) K-feldspar megacrysts to outcrops dominated by variably spaced S/C fabric, especially where it is adjacent to basalt and volcaniclastic sediments. The granite was passively emplaced during the late Early Silurian into domes in the multiply deformed Ordovician turbidites and volcanics of the Macquarie Arc. During cooling and saussization minor epidote-quartz veins formed in the granite. These were preferentially deformed in the late Middle Devonian Tabberabberan orogenic event ( 380 Ma). This resulted in the pervasive S/C fabrics and mylonitisation of parts of the pluton. Exhumation may have been facilitated by early Devonian extension, later 380 Ma thrusting and/or a final phase of deformation during the Early Carboniferous. 2013-03-28T02:22:32.027Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24984 A U-Pb/Hf-isotope study of >16,000 zircons shows that 70% of Earth's continental crust probably formed in Archean time, and much probably is >3 Ga old. The model ages (TMA ) of ca 500 low-Re/Os sulfides in mantle-derived peridotite xenoliths, mainly from the Kaapvaal, Siberian and Slave cratons, peak between 2.5-3.0 or 3.0-3.5 Ga, depending on locality. At each locality the oldest TMA of mantle sulfides correlate well with the oldest U-Pb ages and Hf model ages of crustal zircons. Younger TMA peaks commonly coincide with later major crustal events. Sulfides in mantle xenoliths are secondary phases, and Os model ages probably are biased toward young ages. Most of the studied sulfides are from garnet-bearing peridotites, and the garnet is generally a secondary phase. In Siberian xenoliths, TMA of sulfides included in garnet are younger on average than those of sulfides included in olivine. However, detailed searches of the most depleted peridotites have revealed very few sulfides with TMA >3.5 Ga, just as the oldest widespread crustal ages are around 3.5 Ga. These data suggest that the oldest crust and the oldest, highly depleted SCLM are broadly coeval, and are interpreted as forming during massive mantle over turns that produced the residual Archean SCLM, providing buoyant "life rafts" that since have supported and preserved the continental crust. The 3.5 Ga over turn event changed Earth's fundamental tectonic behaviour, and truly marks the end of the Hadean period. 2013-03-28T02:22:22.938Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24986 In recent years, a large-scale array of broadband seismographs, so-called China National Seismic Network (CNSN), has been burgeoning across China. This large scale array provides unprecedented opportunities to image lithospheric structures of China at unprecedented resolution. Based on 1-2 years of continuous seismic ambient noise data recorded at more than 600 stations from CNSN and several other temporary arrays across China, A 3-D Vsv model of the crust and uppermost mantle is constructed. The 3-D model exhibits significant apparently inter-connected low shearvelocity features across most of the Tibetan middle crust at depths between 20 and 40 km, most prominent nearthe periphery of Tibet. The prominent LVZs are coincident with strong mid-crustal radial anisotropy in western and central Tibet and probably result partially from anisotropic minerals aligned by deformation, which mitigates the need to invoke partial melt to explain the LVZ observations. The western Yangtze Craton are characterized by relatively thick crust (40 km) overlying a high seismic mantle lithosphere that extends to at least 150 km that may have been the nucleus of formation forthe Yangtze craton in the Archean and presents a present-day obstacle to the eastward expansion of Tibet. The West Yangtze Block contrasts with the thinner crust (30 km) and mantle lithosphere (70-80 km) beneath the eastern Yangtze Craton and South China Foldbelt. Very thin, attenuated lithosphere bounds three sides of the eastern North China Craton (NCC), but somewhat thicker faster lithosphere underlies the central and southern parts of the eastern NCC. 2013-03-28T02:22:22.289Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24987 Recent studies integrating mantle and lower crustal geochronology on deep xenoliths, isotopic data from crustal zircons worldwide, and seismic tomographic imaging of deep lithosphere domains, suggest that >70% of the deep lithosphere formed by 3 Ga. Subsequent tectonism modified the lithospheric mantle causing crustal reworking. The Bockfjord area (NW Spitsbergen, Arctic Norway) provides an ideal natural laboratory to track crust/mantle evolution and tectonism over >3.2Ga. Quaternary alkali-basalt volcanism yields abundant mantle and crustal xenoliths across a majortranslithospheric N-S fault. Zircons from lower-crustal xenoliths (both sides) show mainly Neoarch./Paleoprot. or Paleozoic U-Pb ages and some Hf model ages >3.2 Ga. Metasomatic minerals are common in mantle xenoliths from east of the fault but are rare to the west. Re-Os analysis of sulfides in xenoliths west of the fault show TRD model ages to 3.3 Ga; major populations are 2.4-2.6 Ga, 1.6-1.8 Ga and 1.2-1.3 Ga. However, sulfides in xenoliths east of the fault show maximum TRD of 2.3 Ga with major peaks at 900-1100 and 400-500 Ma, identical to the spectrum of zircon ages of protoliths for exposed gneisses and schists east of the fault. The striking differences in the SCLM on either side of the fault suggest majortranscurrent movement, juxtaposing lithospheric sections that evolved discretely. Archean lower crust overlying Archean SCLM west of the fault suggests coupling of the crust and mantle for 3 Ga. 2013-03-28T02:22:17.690Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:25019 The Western Dharwar Craton in peninsular India comprises a typical Meso- to Neo-Archean granite-greenstone terrain. Detrital zircons from two metamorphosed lithic sandstones in a late basin from the Gadag Greenstone Belt preserve at least eight age populations ranging in age from ca 3.34 to 2.55 Ga, and individual grains as old as ca 3.54 Ga. The zircon provenances for the two samples appear to be the same up to ca 3.25 Ga, with relatively juvenile Hf values largely between zero and depleted mantle values. Zircons younger than 3.25 Ga from one sample have similar Hf values to the older grains whereas the other sample gives only negative values indicative of Hf-evolution in a crustal environment. Source regions younger than ca 3.25 Ga for the two samples were distinctly different. Modelling the Hf isotopic evolution of the detrital zircons suggests two major crust forming events at ca. 3.6 and 3.36 Ga, and some indication of juvenile addition to the crust at ca 2.6 Ga. The maximum sedimentation age of the lithic sandstones is constrained by the youngest detrital zircon population at 2547+ or -5 Ma. Gold mineralization in the belt is dated at 2522+ or -6 Ma and constrains greywacke sedimentation, deformation and metamorphism to a ca 25 m.y. interval. 2013-03-28T02:21:23.117Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:23027 Recent advances in computational petrological modeling provide accurate methods for computing seismic velocities and density within the lithospheric and sub-lithospheric mantle, given the bulk composition, temperature, and pressure within them. Here, we test an integrated geophysical-petrological inversion of Rayleigh- and Love-wave phase-velocity curves for fine-scale lithospheric structure. The main parameters of the grid-search inversion are the lithospheric and crustal thicknesses, mantle composition, and bulk density and seismic velocities within the crust. Conductive lithospheric geotherms are computed using P-T-dependent thermal conductivity. Radial anisotropy and seismic attenuation have a substantial effect on the results and are modeled explicitly. Surface topography provides information on the integrated density of the crust, poorly constrained by surface waves alone. Investigating parameter inter-dependencies, we show that accurate surface-wave data and topography can constrain robust lithospheric models. We apply the inversion to central Mongolia, south of the Baikal Rift Zone, a key area of deformation in Asia with debated lithosphere-asthenosphere structure and rifting mechanism, and detect an 80-90 km thick lithosphere with a dense, mafic lower crust and a relatively fertile mantle composition (Mg# < 90.2). Published measurements on crustal and mantle Miocene and Pleistocene xenoliths are consistent with both the geotherms and the crustal and lithospheric mantle composition derived from our inversion. Topography can be fully accounted for by local isostasy, with no dynamic support required. The mantle structure constrained by the inversion indicates no major thermal anomalies in the shallow sub-lithospheric mantle, consistent with passive rifting in the Baikal Rift Zone. 2013-03-26T01:00:22.594Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24886 Reconstruction schemes of formation conditions of those deposits Mindary and Wim-150 were elaborated in the system: bedrock - weathering crust - intermediate collector - placer. For each element of this scheme, distinguishing characteristics of inner structure, types of minor element distributions and U-Pb dating in primary detrital zircons and late recrystallization rims developed on them were studied with the use of methods (Opt, CL, SHRIMP-II, LA, EPMA and others). It was established that (1) in both deposits detrital zircon cores show polymodal values of U-Pb age in the range of 3000 to 1050 Ma (concordant values are 1190-1000 Ma); (2) later recrystallization rims of zircons of Mindary placers and their bedrocks of Kanmentu belt have concordant age of 6000 Ma, and rims of WIM-150 placers and their primary sources of Ballarat belt are of 400Ma. These data suggest that Ti-Zr sands formation within Murray basin had different history in the frame of common model: stage 1 (pre-metamorphic) -- paleosedimentary accumulation of detrital zircons; stage 2 (synmetamorphic) -- metamorphism and deformation with newly formed recrystallization rims in detrital zircons; stage 3 (postmetamorphic) -- erosion of ancient complexes with removal from them of zircon grains with newly formed recrystallization rims and accumulation in MZ-KZ coastal-marine placers. 2013-03-20T11:13:22.641Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24877 The Guadalupian-Lopingian-Boundary (GLB) is currently placed at 260 Ma and defined by the first occurrence of the conodont species Clarkina postbitteri postbitteri. Near the end of the Guadalupian stage, in the mid-Capitanian a major biotic crisis occurred, which affected both terrestrial and marine organisms. Globally this event is recognised by changes in C and Sr isotope signatures and sea-level regression. However, a detailed chronology of this major event is not fully established. We performed high-precision U-Pb geochronology on zircons from ash layers in eastern Australian basins to place the GLB and the extinction horizon in eastern Australia. Drill core and outcrop samples were collected from the Sydney and Gunnedah Basins. Zircons were analysed by chemical abrasion ID-TIMS, which has an age resolution at the sub-permil level. In the Sydney Basin the boundary interval occurs between the Broughton Formation (263.4 Ma) and the Fairford Formation (257.3 Ma). In the Gunnedah Basin the GLB is above the Watermark Formation (262.4 Ma) and below the Pamboola Formation (255.9 Ma). Further ongoing studies of additional ash layers in core and outcrop sections will hopefully allow us to better constrain the GLB in the eastern Australian basins. 2013-03-20T11:11:07.188Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24881 Stagnant lid convection is generally identified as an end-member state of planetary evolution, applicable to old, cold worlds with thick lithosphere and sluggishly convecting interiors which are unable to generate sufficient stress to break the thick immobile lid. However, recent results have shown stagnant lid regimes can also occur forvery hot planets; here high internal temperatures results in low mantle viscosities, and the stress coupling between the vigorously convecting mantle and plates breaks down, leading to stagnation of a thick lithosphere. The implication of these two stagnant end-members is that plate tectonic may be an impermanent tectonic regime in planetary evolution, between two stagnant lid extremes. To test this hypothesis we ran a suite of convection simulations over a range of basal temperatures and internal heating rates, and show that for high ratios of internal to basal heating, applicable to the Hadean, stagnant lid convection is the stable tectonic regime. We also ran a number of evolutionary models, where the basal temperatures and internal heat production decay through time. While sensitive to the starting state, the simulations show an evolution from stagnant lid convection, to an episodic subduction regime, through to continuous plate tectonics, and finally to a cold stagnant lid mode; implying plate tectonics is a transient phase in planetary evolution. 2013-03-20T11:10:54.099Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24885 The Qaidam basin preserves a denser, stronger and seismically faster lower crust with a shallower Moho than other Tibetan terranes. Its northern part is widely believed to have undergone an early Paleozoic continental subduction down to >100 km. What kind of basement can result in such deep subduction and unusual geophysical features? U-Pb ages, trace-element and Hf-isotope compositions of zircon in eclogite and gneiss from the oldest strata of the North Qaidam orogen were analysed, to probe the nature of basement and its link with continental deep subduction. Gneissic zircons yield a wide age spectrum from 2016 to 430 Ma. Their wide range of Hf (t) (+16.0 to -17.5) suggests additions of depleted-mantle (DM) components at 0.8 Ga into an evolved basement as old as 2.5 Ga. Eclogitic zircons show mostly early Silurian ages (442 Ma) with minor Neoproterozoic ages (785 Ma). Mineral inclusions, trace-element patterns and Hf isotopes reveal that the 440-Ma zircons were formed during UHP eclogite-facies metamorphism and recrystallized in 785 Ma igneous precursors. Variations of Hf (t) from +14.2 to -19.2 indicate basaltic protoliths for the eclogites involving large-scale intracontinental mixing between DM-derived magmas and ancient materials at 1.0-0.8 Ga. This magmatism and coeval igneous events in the gneisses probably endowed the Qaidam basement with a denser and stronger framework, which was a prerequisite for deep subduction and its present geophysical proper ties. 2013-03-20T11:10:32.723Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24887 The Hongguleleng Formation records the rapid rebound from the Frasnian-Famennian (F/F) extinction event in a highly fossiliferous shallow marine setting associated with a Devonian oceanic island arc complex. Samples were collected from the basal six meters of shale and limestone in the Hongguleleng Formation and the upper one meter of shale and volcaniclastic sandstone in the underlying Zhulumute Formation. This interval also spans the linguiformis / triangularis conodont zone boundary which forms the F/F boundary. Although the Kellwasser event is not recognizable in outcrop by evidence of black shale, it can be recognized geochemically as series of dysoxic and anoxic events that span three meters of section below the F/F boundary. The same interval also shows high levels of biological productivity based on excess Ba and P2 O5 proxies. The upper limestone surfaces in this interval often have large concentrations of brachiopods. In contrast, limestones and shales in the lower Famennian show oxic to slightly dysoxic conditions. Pulses of volcaniclastic and hydrothermal components to detrital sedimentation are common throughout the interval. The analysis of multiple geochemical proxies allows us to confirm the presence of the Kellwasser event in the open oceanic part of Paleotethys. The tectonic setting of the Hongguleleng Formation is in contrast to the sections previously studied, which were located near Laurussia, Gondwana, Siberia, and the South China plate. 2013-03-20T11:10:28.033Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24890 Simultaneous recovery of complex geometry and unknown magnetization direction from inversion of magnetic field data poses considerable challenges. Never theless a range of methods address such problems and solutions are feasible. We illustrate application of several methods to the magnetic anomaly over a reversely magnetized ring dyke in the Permo-Carboniferous Newcastle Range Volcanics of northern Queensland. Palaeomagnetic study of these rocks isolated two steep reverse magnetization directions of Permian and mid-Carboniferous ages and it is clear from the magnetic field anomaly that one of these dominates the total magnetization. To recover the magnetization direction we first applied magnetic moment analysis (MMA). MMA is best applied to compact sources and must be located over the centre of magnetization. We had hoped that the circular symmetry of the ring dyke might enable this analysis to succeed, but it was disrupted by the eccentric distribution of magnetization in an annulus and produced consistently low inclination values. We then applied several methods which scan a range of trial magnetization directions, applying reduction to pole or equatortransforms from which the optimum value of a chosen statistic is taken to specify the best magnetization direction. These methods are less sensitive to distribution of magnetization and provided superior recovery of inclination, but with inconsistent declination values. Finally we applied inversions which recovered inclinations close to the palaeomagnetic measurements, but again with uncer tain declination values. Further forward modelling with test magnetization directions confirmed the higher sensitivity in recovering inclination rather than declination of magnetization from this anomaly. 2013-03-20T11:10:24.218Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24897 Interpreted time scales for Proterozoic orogenic systems suggest they developed over 10's of million to 100 million years and imply, at a first order, a relatively consistent tectonic regime (ie. crustal shortening). These time scales conflict with modern tectonic systems where: (1) individual events occur over several million years; and (2) tectonic mode switches are common, especially at convergent margins. We detail geological observations, geochronology, and geophysical interpretations from the Gawler Craton and Mount Painter Inlier to illustrate rapid changes in tectonic regime at the Paleo-Mesoproteroic boundary of eastern and southern Australia. Our data suggest that crustal shortening associated with the Wartakan Orogeny (Gawler Craton) and the Olarian Orogeny (Curnamona Province) (ca 1611-1592 Ma) was followed by a switch to crustal extension, intense magmatic activity and crustal anatexis (ca 1595-1580 Ma), and uplift in the Gawler Craton. In the Mount Painter Inlier this extensional switch is recorded by ca 1592 Ma rapid clastic sedimentation with material derived from the Gawler Craton. These sedimentary rocks were subsequently buried to mid crustal levels and exhumed in approximately 5-10 million years during the Painter Orogeny. Shallow level magmatic rocks were then emplaced between ca 1575 Ma and 1552 Ma coincident with renewed metamorphism, which possibly correlated with the Kararan Orogeny identified in the northern Gawler Craton. We suggest that rapid tectonic mode switches were prevalent in the Proterozoic and, although these likely occurred on modern time-scales, are difficult to recognise due to poor preservation of different crustal levels and complex over prints. 2013-03-20T11:10:13.388Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24474 The investigation focus is to determine in the primitive Southern Kermadec basalt, (SiO2 = 49.64%, Mg1.2, MgO = 9.10wt%, normative olivine = 14.58%) the stable mineral assemblage at pressures of 0.5-1.5GPa, temperatures of 1100-1200 C and varied H2 O contents. These data will be used to make an informed hypothesis as to whether the basalt represents a primary melt composition i.e an unmodified result of peridotite melting in the Southern Kermadec arc. Little work has been done on the origin of the more primitive magmas or on the type of mantle they originate from. This is important to understand the nature of the evolution of the Kermadec arc system. A piston cylinder solid media apparatus was utilised and 3.5wt% H2 O was added to the capsule because this is what has been shown to be common in the mantle wedge in arc systems and from the composition of the basalt, is likely to be close to the original magma water content. Results from mineral and glass analysis show H2 O and Fe play significant roles in the crystallisation of the minerals present in the sample. Upon completion of this investigation, we will be able to characterise the parental magma source of the basalt and comparisons can be made to other known volcanic compositions in the area. 2013-03-06T08:04:56.759Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24477 The Fortescue Group contains little-metamorphosed sediments deposited in marine and continental (fluvial and lacustrine) environments between 2775-2630 Ma, preserving a detailed record of environmental conditions and biological processes during the Neoarchean. The Tumbiana Formation of this group was deposited at 2720 Ma, during an episode of increased volcanic activity and tumultuous change in global geological and biological systems. It is well-known for its preservation of a large delta 13C anomaly and remarkably well-preserved, diverse and abundant stromatolites, as well as much of the earliest evidence many modern geobiological cycles, including some of the earliest evidence for oxygenic photosynthesis. Microbialites of the Tumbiana Formation offer clues to the biological affinities of some microbialite-constructing microorganisms at this time, and strongly imply the presence of motile and filamentous organisms occupying an ecological niche that is today occupied by cyanobacteria. I will discuss recent findings relating to informative microbialite morphologies of the Tumbiana Formation. In addition, I will introduce stromatolitic units of the 2.74 Ga Kylena Formation and 2.63 Ga Jeerinah Formation, Fortescue Group, and discuss how the study of these units is providing us with an improved understanding of the timing and significance of evolutionary events recorded in the Tumbiana Formation. 2013-03-06T08:04:52.497Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24476 Developments in in-situ high precision isotope ratio measurements are revolutionising our understanding of the geodynamic Earth at all scales. Laser ablation (LA) multi-collector (MC-) ICP-MS provides spatially resolved data for geochemistry and geochronology that can be interpreted in a microstructural context. One example of the application of the in-situ method is to study the Re-Os isotope systematics of individual sulfide grains and Os-Ir alloys in mantle peridotites. Mantle sulfides are time capsules and they provide a record of multiple events in the lithospheric mantle. Although instrumentation and analytical protocols have advanced significantly in the past decade there is an on-going challenge to optimize accuracy and precision while improving spatial resolution in order to constrain the timing of these events. Further improvements in the in-situ methodologies using LA-MC-ICP-MS require a more rigorous treatment of measurement uncer tainties and error budgets. Many factors contribute to the internal and external precision of in-situ measurements: sample composition, laser characteristics and operating conditions, and processes in the ICP and mass spectrometer. Analyses of a suite of synthetic NiS beads with different Re/Os ratios are used to demonstrate how accuracy and precision are affected by the total beam intensities of Re and Os, the Re/Os ratio, detector calibration and linearity, and the degree of Re/Os fractionation during ablation. 2013-03-06T08:04:46.269Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24480 Reappraisal of overlapped areas of Ti-Zr provinces of Australia and Russia for cost-effective Ti-Zr placers was made by joint research of IMGRE and Macquery University on the basis of boundary parameters and criteria of prediction, search for, and appraisal of Ti-Zr. The sites selected for comparative research were recent and ancient placers of West Australia Province, Eucla Basin Province, and paleo Murray Basin, as well as Russian Cretaceous and Neogene Ti-Zr placers of East European Province, Neogene placers of Northern Caucasus (Scythian) Province, Cretaceous and Paleogene placers of Western Siberia and Eastern Ural Provinces. Studies of the system "bedrock - weathering crust - intermediate collector - commercial placer" comprised: structural-geomorphologic and paleofacies reconstructions of the territory of provinces; analysis of material composition and distribution of useful components; combined studies into type morphology and isotopic and geochemical characteristics of zircon, ilmenite, rutile and other minerals in all the components of the system, revealing alteration trends during transit from bedrock source to sedimentary basin. As a result of conducted structural geomorphological and paleo facial reconstructions of provinces, a distinct relation was established between the ranked forms of modern relief and corresponding ranks of major elements of substratum geology affecting the formation and persistence of Ti-Zr placers. Forecast maps were constructed for economic Ti-Zr placers. The elaborated and tested complex of research is least time-consuming and least expensive for appraising the prospects for buried industrial placers of overlapped areas at an early stage of studying them. 2013-03-06T08:04:35.816Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24485 IODP Expedition 317 drilled 4 sites on a landward-to-basinward transect in the Canterbury Basin off New Zealand. Site U1354 was drilled on the mid-shelf (48 km offshore), while site U1352 was on the continental slope (67 km offshore). Cored Holocene-Miocene sediments from the seafloor down to 1.8 km were analysed for their biomarker composition. Extractability of the sediments is low (<0.6 mg EOM/g sediment), consistent with the generally low TOC (<1.5%). n Alkanes are typically most abundant in the C23 -C33 range and are strongly dominated by the odd carbon numbered homologues, reflecting substantial higher plant input. Based on Pr/Ph, oxicity of the depositional environment was high on the shelf, but much less so on the slope. Biomarker distributions include immature hopanes, especially the C31 22R isomer, and sterane distributions dominated by C29 isomers. The presence of aromatic biomarkers such as cadalene is consistent with a strong terrestrial organic matter contribution, and it is notable how little marine organic matter is apparently preserved, as also shown by low hydrogen indices (<100 mg HC/g TOC). Thermal maturities for a sample from 1,554 m in U1352, based on calibrated aromatic hydrocarbon maturity ratios, indicate a calculated reflectance of 0.57%, and this is supported by the Tmax of 420-430 C. This thermal maturity just prior to the start of the oil window supports a high geothermal gradient of 45 C/km in this part of the Canterbury Basin. 2013-03-06T08:04:26.363Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24486 Inferences on subsurface temperatures in geothermal studies, based on sparse datasets and modelling, contain many sources of significant uncer tainty. Further, a problem arises in the scale of computation needed for data-driven inference when an inversion is posed on geodynamical constraints, such as heat flow over basins or systems of basins. Here we outline an approach to understanding the sensitivity in model parameters in a forward modelling suite of a basin-scale geothermal problem, which allows the fundamental controlling parameters in the problem to be identified and constrained. We have been improving this approach and making our implementations much more readily available to the community. An example of this approach was first done for the Sydney Gunnedah basin model. We've extended this work with updates to the method implementation and extrapolations to include the Bowen basin. 2013-03-06T08:04:23.486Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24490 Acid mine drainage is a significant environmental hazard. Highly acidified water in affected sites causes a range of environmental issues including accumulation of heavy metals, loss of biodiversity and, particularly in sites with coal-mining history, greenhouse gas emissions. In acid mine drainage sites related to coal mining, methane and carbon dioxide are formed by the microbial decomposition of coal under anaerobic conditions. To date, much of the work on acid mine drainage has focused on the microbiology and biogeochemistry of the surface water, and little is known about the microbiological processes occurring in the anaerobic sediments associated with these environments. Therefore, to better understand these processes, we have used Illumina-based metagenomics to examine the microbial diversity of the anaerobic sediment zones in a coal-fueled acid mine drainage system in the Hunter Valley, NSW, Australia. The microbial community composition of these environments along with the physiological potential of the organisms in these communities will be discussed. 2013-03-06T08:04:17.849Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24493 The drifting of Australian landmass from Greater India around 136 Ma resulted in large volumes of volcanic eruptions in the Indian Ocean and surrounding continental margins. This was followed by later episodes of submarine eruptions. Evidence of this volcanism can be seen in the form of two exposed islands, Christmas Island and Cocos (Keeling) Island, and numerous submerged seamounts. Christmas Island is dominated by limestones and phosphates with some basalts and basanites. The island experienced three stages of volcanic activity the oldest one in Late Cretaceous followed by later phases in the Eocene and in the Miocene. Four sites were selected for paleomagnetic sampling, three on east and one on west coast. Samples were demagnetised using alternating field progressive demagnetisation with increments up to 70 mT. Characteristic Remanent Magnetisation was determined using PCA to remove low stability component. Fisherian statistical analysis gave two different mean inclinations (Im ) of 71 for Waterfall Spring & Dolly Beach and 55 for Winifred & Ethel Beach. The higher Im of the former sites could be due to lightening strikes that disturbed the original magnetic character. These Im were used to constrain the paleo-latitudes of the island using equation tan Im =2 tan . Steeper inclination gave a paleolatitude of 54 S where as shallower inclination gave 36 S which lies in conformation with the position of island observed in plate reconstruction models at approximately 50-65 Ma. 2013-03-06T08:04:17.146Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24492 Surface feature morphology can reflect the lithospheric and rheological structure as well as the deformational processes of a region. On Venus the lithospheric structure is poorly known. Also, Venus' lack of surface water, high surface temperatures and pressures produce unique rheological conditions. As a result, the deformational processes that have acted, particularly within complex ridged terrain, are varied. We aim to constrain the deformational processes, lithospheric and rheological structure at the volcanic rises of Atla and Beta Regio as well as the complex ridged terrain of Fortuna Tessera. We have used LitMod3D and data sets from Magellan to constrain a proposed lithospheric structure below each of these regions. Most of the central rise topography at Atla and Beta Regio could be isostatically compensated by a thin thermal lithosphere, whilst Fortuna Tessera can be characterised by a thicker thermal lithosphere. LitMod3D also provides estimates of surface heat flow, temperature, density and pressure distributions, which were used as rheological controls in our numerical models. Our simulations show that rheology varies between our different areas and their associated defomational processes. By constraining the lithospheric structure and rheology below each of these areas we have consequently restricted the deformational processes that could have acted to sculpt the surface. 2013-03-06T08:04:16.022Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24498 The Indian-Eurasia continental collision has led to the uplift of the Tibetan Plateau, and various competing models have been proposed to explain the rise and growth of the Tibetan plateau. The best place to address the growth of the Tibet plateau and to test the competing models is the northeast Tibetan plateau. What causes the rise of the northeast Tibetan plateau? Is it the mid-crustal flow, the coherent thickening of the Tibet lithosphere, or the subduction of the Eurasian blocks? Therefore, we combined both ambient noise data and earthquake Rayleigh wave data to estimate both the group velocity structure and the S-wave velocity structure across the northeastern margin of the Tibetan Plateau (E88 -108 , N32 - 42 ). Our preliminary results show that in the crust, the low-velocity anomaly beneath the Tibetan Plateau has not been observed beneath the Qaidam basin, south Kunlun block and Qinling Orogen, suggested that the eastern KunLun fault interrupted the crustal low-velocity flow. However, our results display that the low-velocity zone appears beneath the Qilian Orogeon, suggestive of complex tectonic processes in the northeastern margin of the Tibetan Plateau. In the upper mantle, from 150 km to 250 km, our shear wave velocity model shows a low velocity channel beneath the Qaidam-Qilian-Qinling block which may represent the asthenosphere. We also did some inversion tests for the anisotropy parameters. Our preliminary results show that the dominant fast direction is NWW-SEE, generally consistent with the SKS splitting results. 2013-03-06T08:04:06.373Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24503 The physical state of the Earth during the Hadean was characterized by 1) heavy bombardment episodes; 2) extremely high internal heat production in crust and mantle rocks, and 3) high temperatures left over from Earth and core formation processes. Taken together, a strong case is made for extremely high internal temperatures, low internal viscosities, and extremely vigorous mantle convection. Previous studies of mixing in high-Rayleigh number convection indicate that chemically heterogeneous mantle anomalies should have efficiently remixed into the mantle on timescales of less than 100Myr. However, Nd isotope studies indicate that heterogeneous mantle domains survived, without mixing, for over 2Gyr -- at odds with mixing rates expected. Similarly, PGE concentrations in Archaean komatiites, purportedly due to the laterveneer of meteoritic addition on the Earth, only achieve current levels at 2.7Ga -- indicating a time lag of almost 1-2Gyr in mixing this material thoroughly in the mantle. Plausible mixing retardation mechanisms include layering of mantle convection, anomalously viscous blobs of material, or the cessation of tectonic resurfacing mechanisms. Here we show that layered convection is limited in models with strong tectonic plates, and argue that high viscosity blobs are undemonstrated. In contrast, a number of lines of evidence suggest resurfacing in the Archaean was episodic, and extending these models to Hadean times implies the Hadean was characterized by long periods of tectonic quiescence. We show that mixing in stagnant lid regimes is, at the extreme, over an order of magnitude less efficient than mobile lid mixing, which may explain unduly long mixing times recorded in the Hadean/early Archaean. 2013-03-06T08:03:57.796Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24506 The central Alpine-Himalaya collision is characterised by two mountains belts, Zagros and Himalaya, and its plateaus. Although being the results of the same process, some differences have been noticed since their total amount of convergence is different and Zagros seems to be in a more recent stage of development. A thinning of the lithosphere has been proposed for both Zagros and Tibet to fit potential field data and to explain the high elevation, low seismic wave velocities in the upper mantle, low Pn velocities, higher wave attenuation and higher crustal temperatures than in the surrounding shields. The study of these belts' present-day structures provides new insights into different evolution steps of a collisional process. Combining geophysical and petrological data, we study the lithospheric structure down to 400km depth along three transects, two crossing the Zagros, and the third crossing the Himalayan front up to the Tibetan Plateau. In the Zagros the results show a lithospheric mantle thinning affecting the whole area beneath the range, more extended in the southern sector. It lengthens to the Alborz and the Central Plateau. A Phanerozoic mantle composition denotes the mantle below the range. In the Himalayan belt a more evolved composition should be expected since India-Eurasia collision occurred prior to the Arabia-Eurasia one and since the average convergence rates between the former are higher that the latter. A comparison between the Zagros and Himalaya profiles will be performed in order to discuss the LAB geometry and the compositional differences in the two collisional environments. 2013-03-06T08:03:50.135Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24509 The North China Craton (NCC) is a typical case of destruction of the ancient cratons in the world. However, the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversial on the destruction time, which is undoubtedly the key to understand the destruction processes. Based on temporal and spatial distribution, sources and tectonic setting of magmatism, it is recognized that five stages of magmatism and tectonism occurred in the NCC during the Phanerozoic, i.e., Carboniferous to Early Permian, Late Permian to Middle Triassic, Late Triassic, Jurassic and Early Cretaceous. The first four stages of magmatism and tectonism, related to the southward subduction of Paleo-Asian plate and the assembly of Sino-Korean and Yangtze cratons, are locally distributed in small parts of the NCC, reflecting a multiple stage modification of the NCC during Late Carboniferous to Jurassic. However, the intensive development of the Early Cretaceous magmatism, extensional deformation and associated gold mineralization, with significant continental crustal growth indicate that the eastern NCC had been destroyed during this time of period. This destruction was deduced from the Paleo-Pacific subduction beneath the eastern Asian continent, with lithospheric removal and/or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere. 2013-03-06T08:03:45.292Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24511 In situ U-Pb and Lu-Hf data on detrital zircons from Proterozoic sediments have been used to gain a clearer picture of the tectonic background and crustal evolution in the western part of the Yangtze Block. The youngest concordant zircon ages for sedimentary units suggest maximum depositional ages of 1014 Ma for the Kunyang Group, 750649 Ma for the Sinian sequences, and 525 Ma for the Cambrian sediments. The Yinmin Formation, previously assigned to the Kunyang Group, was actually deposited after 1667 Ma and contains zircons whose ages are dominantly from late Archean to Paleoproterozoic (2.72.8 Ga, 2.52.3 Ga and 1.85 Ga). The Heishantou Formation in the lower part of the Kunyang Group has two major age populations of 1.0 Ga and 1.61.8 Ga. The Sinian and Cambrian sedimentary rocks are dominated by Neoproterozoic zircons with age peaks at 760 Ma and 825 Ma. The Lu-Hf isotope data suggest that a significant juvenile input took place during Archean and Neoproterozoic, respectively, while crustal reworking was dominant during Paleoproterozoic. The Archean-Paleoproterozoic detritus is isotopically distinct from the coeval basement exposed in northern Yangtze Block, suggesting that a subarea of old crust lies beneath the young sediments covering the craton. The presence of abundant 1.85 Ga zircons suggests that the Yangtze Block was probably part of the Columbia supercontinent during Paleoproterozoic, and could have been adjacent to the North China Craton and/or Australia. 2013-03-06T08:03:41.482Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24513 It has also long been recognized that major changes occur in the geologic record between 3.0 and 2.5 Ga, all of which must be accommodated in any thermal model for Earth. In addition, Hf isotopic model ages suggest that between 50 and 70% of the continental crust was produced during this time interval. Also coinciding with this time window are a maximum in mantle potential temperature and the degree of melting of the upper mantle, a minimum in lithosphere thickness and density, and a crossover between the minimum subductable thickness of oceanic lithosphere and the equilibrium lithospheric thickness for a stagnant lid thermal regime. We suggest that changes during this time interval may all be related to a change from an active stagnant lid to a plate tectonic cooling regime in the mantle and that zircon age peaks, which are superimposed on Earth's cooling curve, reflect collisional preservation events during the supercontinent cycle beginning about 3 Ga. Earth may have evolved through three stages: 1) first is an early active stagnant lid regime that began after the magma ocean phase (following the moon-forming event) and lasted until about 3.5 Ga; 2) the mantle then transitioned into an episodic regime characterized by alternating stagnant lid and plate tectonic phases between 3.5 and about 2.2 Ga, with plate tectonics becoming very widespread between 2.7 and 2.5 Ga; the final stagnant lid regime occurred from 2.4-2.2 Ga; and lastly, 3) the modern plate tectonic regime which continued from 2.2 Ga to the present. 2013-03-06T08:03:37.579Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24515 Polished plates of diamondites (polycrystalline diamond aggregates) from Africa and in eclogites from Lesotho, were prepared for study of internal structure and in-situ geochemical analysis, to understand diamond-forming processes. The diamondites in eclogites are enclosed in large garnet grains, while monocrystalline diamonds occur in cpx-bearing metasomatic veins that crosscut the garnets. CL imaging and Electron BackScattered Diffraction (EBSD) show that diamondites underwent plastic deformation, recrystallization and grain-size reduction under mantle conditions. Therefore they should not be interpreted as products of primary crystallisation. Oxygen-isotope analysis of interstitial garnets and zoning in carbon isotope composition indicate that the diamondites have been deformed and recrystallised during the penetration of mantle fluids/melts, which provided carbon for the formation of diamond in metasomatic veins. Interstitial silicates reacted with metasomatic fluids percolating along diamond grain boundaries; interstitial garnets have higher mg0.78) than original inclusions (0.70 to 0.53). The REE patterns of eclogitic garnets become flatter (higher LREE/HREE) with increasing metasomatism. The compositions of large garnet grains from Lesotho (mg.78-0.82) are similarto those of interstitial garnets from diamondites. Coexisting cpx and gnt inclusions from the least deformed diamondites give T=1200 C for diamond formation. 2013-03-06T08:03:33.781Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24517 Three types of garnet (Gnt) can be recognised in eclogites from the Udachnaya kimberlite pipe, with different major-, trace-element and O-isotope compositions and related to different stages of mantle metasomatism. Gnt1 and Gnt2 are usually found together with diamonds in metasomatic veins. Gnt2 forms Mg-rich rims on Gnt 1 (mg.67-0.80 vs 0.57-0.58 for Gnt1). The significant zoning in chemistry and its relationship to diamond with mantle-like carbon (13 C = -5.6 - -6.6) suggest that Gnt2 was produced by mantle fluids/melts shortly before eruption. Gnt2 has a wide range in oxygen isotope composition (18 O = 6.2-9.0), suggesting mixing of mantle fluids with the original isotopic system (Gnt1, 18 O =11.1-12.0). Gnt3 is found in corundum-bearing eclogites and has much higher Ca (CaO=15.61-16.56 wt%) and different isotopic characteristics (13 C = -3.6 - -5.3; 18 O = 3.2-5.7). This suggests a different metasomatic fluid from the one that produced Gnt2. Lu/Gd increases significantly from Gnt3 (0.06-0.12) to Gnt1 (4.0-4.2) to Gnt2 (5.5-9.0). The major- and TE compositions of garnets from 25 eclogites show a well-defined change from positive to negative HREE/LREE at a CaO content of 7.8-8.7%. This suggests either a change in fluid compositions or a change in Gnt/fluid partitioning related to garnet composition. 2013-03-06T08:03:28.465Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24521 Anisotropy arises in mechanics and other fields of science as the deviatoric-symmetric parts of various tensor quantities and is a frequently measurable physical proper ty of naturally deformed rocks. This presentation discusses homogeneous anisotropies of a real second-order tensor nature and asks whether any one graphical representation of form and intensity is fundamental and facilitates linear statistical analysis. The question has practical application to the problem of superposed anisotropies in geological materials and is of interest for representation of deviatoric second-order tensors generally. Geometric tensors such as homogeneous finite strain and second-order mineral-orientation density are members of what mathematicians call Lie groups that can be mapped into corresponding lineartensors by logarithmic operations. The deviatoric part that is of interest here lies at a unique position with respect to the projections of defined principal axes in an octahedral plane, sometimes called a three-axis plane. Thus vector addition and linear statistics can be applied to points in this plane, including points defined by the projections of logarithms of principal components of deviatoric geometric tensors. The logarithmic octahedral projection can assist not only in separating tectonic and initial components of anisotropy, such as in deformed sedimentary rocks, but also in providing information about the underlying lineartensor relating to average deformation styles and transport directions in tectonic zones. The method is discussed for monoclinic transpressive and transtensional non-coaxial progressive deformations of an orthogonal bedding anisotropy and compared with some of the more commonly used graphical plots. 2013-03-06T08:03:24.421Z ]]>