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Subject: 地球科学::地质学
Title: Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications
Author: Griffin, WL (Griffin, W. L.)1, 2; Afonso, JC (Afonso, J. C.)1, 2; Belousova, EA (Belousova, E. A.)1, 2; Gain, SE (Gain, S. E.)1, 2; Gong, XH (Gong, X. -H.)3; Gonzalez-Jimenez, JM (Gonzalez-Jimenez, J. M.)1, 2, 4, 5; Howell, D (Howell, D.)1, 2; Huang, JX (Huang, J. -X.)1, 2, 6; McGowan, N (McGowan, N.)1, 2; Pearson, NJ (Pearson, N. J.)1, 2; Satsukawa, T (Satsukawa, T.)1, 2; Shi, R (Shi, R.)1, 2, 3; Williams, P (Williams, P.)7; Xiong, Q (Xiong, Q.)1, 2, 8; Yang, JS (Yang, J. -S.)9; Zhang, M (Zhang, M.)1, 2; O'Reilly, SY (O'Reilly, Suzanne Y.)1, 2
Corresponding Author: Griffin, WL
Source: JOURNAL OF PETROLOGY
Issued Date: 2016
DOI: 10.1093/petrology/egw011
Volume: 57, Issue:4, Pages:655-684
Indexed Type: SCI
Cooperation Status: 国际
DOC Type: Article; Proceedings Paper
English Abstract: Large peridotite massifs are scattered along the 1500 km length of the Yarlung-Zangbo Suture Zone (southern Tibet, China), the major suture between Asia and Greater India. Diamonds occur in the peridotites and chromitites of several massifs, together with an extensive suite of trace phases that indicate extremely low fO(2) (SiC, nitrides, carbides, native elements) and/or ultrahigh pressures (UHP) (diamond, TiO2 II, coesite, possible stishovite). New physical and isotopic (C, N) studies of the diamonds indicate that they are natural, crystallized in a disequilibrium, high-T environment, and spent only a short time at mantle temperatures before exhumation and cooling. These constraints are difficult to reconcile with previous models for the history of the diamond-bearing rocks. Possible evidence for metamorphism in or near the upper part of the Transition Zone includes the following: (1) chromite (in disseminated, nodular and massive chromitites) containing exsolved pyroxenes and coesite, suggesting inversion from a high-P polymorph of chromite; (2) microstructural studies suggesting that the chromitites recrystallized from fine-grained, highly deformed mixtures of wadsleyite and an octahedral polymorph of chromite; (3) a new cubic Mg-silicate, with the space group of ringwoodite but an inverse-spinel structure (all Si in octahedral coordination); (4) harzburgites with coarsely vermicular symplectites of opx + Cr-Al spinel +/- cpx; reconstructions suggest that these are the breakdown products of majoritic garnets, with estimated minimum pressures to > 13 GPa. Evidence for a shallow pre-metamorphic origin for the chromitites and peridotites includes the following: (1) trace-element data showing that the chromitites are typical of suprasubduction-zone (SSZ) chromitites formed by magma mixing or mingling, consistent with Hf-isotope data from magmatic (375 Ma) zircons in the chromitites; (2) the composition of the new cubic Mg-silicate, which suggests a low-P origin as antigorite, subsequently dehydrated; (3) the peridotites themselves, which carry the trace element signature of metasomatism in an SSZ environment, a signature that must have been imposed before the incorporation of the UHP and low-fO(2) phases. A proposed P-T-t path involves the original formation of chromitites in mantle-wedge harzburgites, subduction of these harzburgites at c. 375 Ma, residence in the upper Transition Zone for > 200 Myr, and rapid exhumation at c. 170-150 Ma or 130-120 Ma. Os-isotope data suggest that the subducted mantle consisted of previously depleted subcontinental lithosphere, dragged down by a subducting oceanic slab. Thermomechanical modeling shows that roll-back of a (much later) subducting slab would produce a high-velocity channelized upwelling that could exhume the buoyant harzburgites (and their chromitites) from the Transition Zone in < 10 Myr. This rapid upwelling, which may explain some characteristics of the diamonds, appears to have brought some massifs to the surface in forearc or back-arc basins, where they provided a basement for oceanic crust. This model can reconcile many apparently contradictory petrological and geological datasets. It also defines an important, previously unrecognized geodynamic process that may have operated along other large suture zones such as the Urals.
WOS ID: WOS:000379752300003
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Content Type: 期刊论文
URI: http://ir.itpcas.ac.cn/handle/131C11/7719
Appears in Collections:图书馆_期刊论文

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description.institution: 1.Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst, N Ryde, NSW 2109, Australia
2.Macquarie Univ, Dept Earth & Planetary Sci, GEMOC, N Ryde, NSW 2109, Australia
3.Chinese Acad Sci, Inst Tibetan Plateau Res, Key Lab Continental Collis & Plateau Uplift, Beijing 100101, Peoples R China
4.Univ Chile, Dept Geol, Santiago, Chile
5.Univ Chile, Fac Ciencias Fis & Matemat, Andean Geothermal Ctr Excellence CEGA, Santiago, Chile
6.Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, Beijing 100029, Peoples R China
7.Univ Western Sydney, Sch Sci & Hlth, Locked Bag 1757, Penrith, NSW 2750, Australia
8.China Univ Geosci, Sch Earth Sci, State Key Lab Geol Proc & Mineral Resources, Wuhan 430074, Peoples R China
9.Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China

Recommended Citation:
Griffin, WL ,Afonso, JC ,Belousova, EA ,et al. Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications[J]. JOURNAL OF PETROLOGY,2016,57(4):655-684.
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