Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.14/21173
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- Title
- Multiple events in the Neo-Tethyan oceanic upper mantle : evidence from Ru-Os-Ir alloys in the Luobusa and Dongqiao ophiolitic podiform chromitites, Tibet
- Related
- Earth and planetary science letters, Vol. 261, Issue 1-2, p.33-48
- DOI
- 10.1016/j.epsl.2007.05.044
- Publisher
- Elsevier BV
- Date
- 2007
- Author/Creator
- Shi, Rendeng
- Author/Creator
- Alard, Olivier
- Author/Creator
- Zhi, Xiachen
- Author/Creator
- O'Reilly, Suzanne Y
- Author/Creator
- Pearson, Norman J
- Author/Creator
- Griffin, William L
- Author/Creator
- Zhang, Ming
- Author/Creator
- Chen, Xiaoming
- Description
- In situ analysis of major elements, platinum-group elements and Os isotope composition data for 170 grains of Ru–Os–Ir alloys from podiform chromitites in the Luobusa and Dongqiao ophiolites, Tibet, provide new constraints on the sources of the alloy grains, the Os-isotope composition of the Neo-Tethyan oceanic upper mantle, and the timing of melt–rock reactions in the ultramafic peridotites of the host ophiolites. Most alloy grains are osmiridium and iridosmine. Based on elemental and isotopic compositions, two populations can be identified. Group I, found in both ophiolite bodies, has fractionated PGE patterns typical of alloys and homogeneous ¹⁸⁷Os/¹⁸⁸Os 0.12645 ± 4 (2s; n = 145). Group II alloys from the Dongqiao ophiolites show smooth PGE patterns and ¹⁸⁷Os/¹⁸⁸Os ranges from 0.12003 to 0.12194 (yielding Re-depletion ages ≥ 1.1 Ga). Both the PGE patterns and the Os isotopic compositions of Group II resemble those of sulfides residual after melting. Group I alloys represent an early cumulate phase during the crystallization of magmas and are interpreted as derived from an asthenospheric melt. In contrast, Group II alloys are inferred to derive from the breakdown of residual sulfides from the mantle section of the ophiolite, which may represent relics of a sub-continental lithospheric mantle. The coexistence of the two groups of alloys in Dongqiao samples reflects interaction between asthenosphere-derived melts and old depleted lithospheric mantle and suggests that the chromitites originated through melt–rock reactions. The data on the Group I alloys support the hypothesis that the Re–Os evolution of the convective oceanic mantle resembles that of enstatite chondrites.
- Description
- 16 page(s)
- Subject Keyword
- 187Os/188Os mantle composition, Ru-Os-Ir alloys, podiform chromitite, Luobusa ophiolite, Dongqiao ophiolite, Tibet
- Subject Keyword
- ¹⁸⁷Os/¹⁸⁸Os mantle composition
- Subject Keyword
- Ru–Os–Ir alloys
- Subject Keyword
- podiform chromitite
- Subject Keyword
- Luobusa ophiolite
- Subject Keyword
- Dongqiao ophiolite
- Subject Keyword
- Tibet
- Resource Type
- journal article
- Organisation
- Macquarie University. National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC)
- Identifier
- http://hdl.handle.net/1959.14/21173
- Identifier
- ISSN:0012-821X
- Identifier
- mq-rm-2007001167
- Language
- eng
- Reviewed
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