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Recycling of ancient subduction-modified mantle domains in the Purang ophiolite (southwestern Tibet)
Gong, XH (Gong, Xiao-Han)1,3; Shi, RD (Shi, Ren-Deng)1,2,4,5; Griffin, WL (Griffin, W. L.)4,5; Huang, QS (Huang, Qi-Shuai)1; Xiong, Q (Xiong, Qing)4,5,6; Chen, SS (Chen, Sheng-Sheng)1,3; Zhang, M (Zhang, Ming)4,5; O'Reilly, SY (O'Reilly, Suzanne Y.)4,5; Gong, XH
Source PublicationLITHOS
AbstractOphiolites in the Indus-Yarlung Zangbo (IYZ) suture (southern Tibet) have been interpreted as remnants of the Neo-Tethyan lithosphere. However, the discovery of diamonds and super-reducing, ultra-high pressure (SuR-UHP) mineral assemblages (e.g., coesite after stishovite, olivine after wadsleyite, native metals, alloys, and moissanite) in some of these massifs and associated chromitites requires a re-evaluation of their origin and evolution. A new petrological and geochemical study of the Purang ophiolite in the western IYZ suture sheds new lights on these issues.
The depleted harzburgites of the Purang massif have low modal contents of clinopyroxene (<2%), and high Cr# [100*Cr3+/(Cr3+ + Al3+)] in spinel (>40 similar to 70) and pyroxenes (>16 in orthopyroxene, and >20 in clinopyroxene), suggesting high degrees of melt extraction (>20%). These features are not consistent with formation in a (ultra-) slow-spreading mid-ocean ridge. These peridotites have high modal contents of orthopyroxene; this, and the extremely high Cr# of spinels in these peridotites, suggests modification in a subduction zone. The clinopyroxene-rich harzburgites and lherzolites contain rare spinel-pyroxene symplectites after garnet. Their clinopyroxenes have low MREE-to-HREE ratios ((Sm/Yb)(N) < 0.1) at relatively high HREE concentrations, and are Na-rich but Nd-poor. The relatively enrichment of Na but depletion of Nd in clinopyroxene cannot be explained by refertilization with MORB melts but are consistent with an origin from Na-rich subcontinental lithospheric mantle (SCLM). All lines of evidence suggest that these peridotites underwent initial melting in the stability field of garnet-fades peridotites, followed by additional melting in the spinel-facies mantle.
Whole-rock Os isotopic compositions of the Purang peridotites give ancient T-RD model ages (up to 1.3 Ga), indicating that the formation of these ancient depletion residues predated the opening of Neo-Tethyan Ocean. These observations, together with recent studies on other IYZ peridotites, suggest that the Purang peridotites are genetically unrelated to the associated mafic crust. Instead, they represent ancient SCLM domains, initially formed beneath a continental margin, and then modified by subduction, before they were incorporated into the Neo-Tethyan ocean basin. This model is consistent with the deep-mantle-recycling model for the presence of SuR-UHP phases in the IYZ ophiolites. The infiltration of MORB melts through these ancient depleted peridotites during their final exhumation in a (ultra-) slow-spreading center may have refertilized them to produce the clinopyroxene-rich peridotites. (C) 2016 Elsevier B.V. All rights reserved.
Subject Area地质学
WOS IDWOS:000384783500002
Indexed BySCI
KeywordMid-atlantic Ridge Oceanic Upper-mantle Ultrahigh-pressure Chromitites Spinel-pyroxene Symplectite Yarlung-zangbo Suture Melt-rock Interaction Sub-arc Mantle Abyssal Peridotites Trace-element Yungbwa Ophiolite
Cooperation Status国际
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Document Type期刊论文
Corresponding AuthorGong, XH
Affiliation1.Chinese Acad Sci, Inst Tibetan Plateau Res, Key Lab Continental Collis & Plateau Uplift, Beijing 100101, Peoples R China
2.CAS Ctr Excellence Tibetan Plateau Earth Sci, Beijing 100101, Peoples R China
3.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
4.Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst CCFS, Sydney, NSW 2109, Australia
5.Macquarie Univ, GEMOC, Dept Earth & Planetary Sci, Sydney, NSW 2109, Australia
6.China Univ Geosci, Sch Earth Sci, State Key Lab Geol Proc & Mineral Resources, Wuhan 430074, Peoples R China
Recommended Citation
GB/T 7714
Gong, XH ,Shi, RD ,Griffin, WL ,et al. Recycling of ancient subduction-modified mantle domains in the Purang ophiolite (southwestern Tibet)[J]. LITHOS,2016,262(0):11-26.
APA Gong, XH .,Shi, RD .,Griffin, WL .,Huang, QS .,Xiong, Q .,...&Gong, XH.(2016).Recycling of ancient subduction-modified mantle domains in the Purang ophiolite (southwestern Tibet).LITHOS,262(0),11-26.
MLA Gong, XH ,et al."Recycling of ancient subduction-modified mantle domains in the Purang ophiolite (southwestern Tibet)".LITHOS 262.0(2016):11-26.
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