气候变化领域集成服务门户(CCPortal): Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications

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DOI	10.1093/petrology/egw011
	Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications
	Griffin, W. L.; Afonso, J. C.; Belousova, E. A.; Gain, S. E.; Gong, X. -H.; Gonzalez-Jimenez, J. M.; Howell, D.; Huang, J. -X.; McGowan, N.; Pearson, N. J.; Satsukawa, T.; Shi, R.; Williams, P.; Xiong, Q.; Yang, J. -S.; Zhang, M.; O'Reilly, Suzanne Y.
通讯作者	Griffin, WL (通讯作者)
发表日期	2016
ISSN	0022-3530
EISSN	1460-2415
起始页码	655
结束页码	684
卷号	57 期号:4
英文摘要	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.
关键词	ZANGBO SUTURE ZONE ZIRCON U-PB FORE-ARC BASIN ULTRAHIGH-PRESSURE CHROMITITES SPINEL-PYROXENE SYMPLECTITE RE-OS SYSTEMATICS LUOBUSA OPHIOLITE PODIFORM CHROMITITES XIGAZE OPHIOLITE SOUTHERN TIBET
英文关键词	Transition Zone; Tibet collision zone; UHP and super-reducing conditions; Yarlung-Zangbo Suture Zone; geodynamic exhumation; mantle recycling
语种	英语
WOS研究方向	Geochemistry & Geophysics
WOS类目	Geochemistry & Geophysics
WOS记录号	WOS:000379752300003
来源期刊	JOURNAL OF PETROLOGY
来源机构	中国科学院青藏高原研究所
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/258844
推荐引用方式 GB/T 7714	Griffin, W. L.,Afonso, J. C.,Belousova, E. A.,et al. Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications[J]. 中国科学院青藏高原研究所,2016,57(4).
APA	Griffin, W. L..,Afonso, J. C..,Belousova, E. A..,Gain, S. E..,Gong, X. -H..,...&O'Reilly, Suzanne Y..(2016).Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications.JOURNAL OF PETROLOGY,57(4).
MLA	Griffin, W. L.,et al."Mantle Recycling: Transition Zone Metamorphism of Tibetan Ophiolitic Peridotites and its Tectonic Implications".JOURNAL OF PETROLOGY 57.4(2016).