The Boninite-like Dolerites in the Xigaze Ophiolites, Tibet: Similar to the MORB-like Dolerites

作     者：YANG Shengbiao YANG Jingsui LI Yuan LI Ruibao 

作者机构：Center for Advanced Research on the Mantle(CARMA)Key Laboratory of Deep-Earth Dynamics of Ministry of Land and ResourcesInstitute of GeologyChinese Academy of Geological SciencesBeijing 100037 School of Earth Sciences and ResourcesChang’an UniversityXi’anShaanxi 710054 

出 版 物：《Acta Geologica Sinica(English Edition)》 (地质学报（英文版）)

年 卷 期：2020年第94卷第S01期

页      面：73-75页

核心收录：

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

基　　金：co-supported by the National Key Research and Development Project of China(No.2016YFC0600310) funded by the China Geological Survey(CGS No.DD20160023) the Natural Science Foundation of China(41802055) the project from the China Postdoctoral Science Foundation(2018M632942) 

主　　题：Yarlung Zangbo suture zone Xigaze ophiolite depleted mantle mid-ocean ridge 

摘      要：The Early Cretaceous Xigaze ophiolites(XO)exposed along the central segment of the more than 2000 km long Yarlung Zangbo Suture Zone in southern Tibet,preserved the structure of the upper mantle and oceanic crust,is interpreted as a definite record of Neo-Tethys oceanic *** evolution models of the XO have been proposed since the 1980s(Nicolas et al.,1981;Hébert et al.,2012;Maffione et al.,2015).However,the geodynamic environment of the XO whether at a MOR or SSZ remains *** key evidence for the identification of the SSZ ophiolite,the boninite-like dolerites from the XO are still controversial and poorly constraint(Chen et al.,2003;Bao et al.,2013;Dai et al.,2013).According to previous reports,dolerites were subdivided to MORB-like type and boninite-like type(Chen et al.,2003;Dai et al.,2013).Apart from high-SiO2(52 wt%),high MgO(8 wt%)and low-TiO2(0.5 wt%),we found the boninite-like and MORB-like dolerites are indistinguishable in outcrop,mineral and *** are sills invaded into mantle sequence of the XO,with 50.35–56.80 wt%SiO2,0.32–1.19 wt%TiO2,7.39–8.89 wt%Fe2O3T,5.50–10.42 wt%MgO and Mg#of 0.49–***-like dolerites display trace element and REE patterns similar to those of most fore-arc or/and back-arc basalts from Izu-Bonin-Mariana(IBM),*** in large ion lithophile elements(LILEs,***,Rb,Ba,Pb,U)and depletion in high-field strength elements(HFSE,Nb,Ta)(Fig.1).Boninite-like dolerites resemble the MORB-like dolerites in trace elements and REE patterns,excepting for lower concentrations in REE,but distinct from the boninites discovered from the IBM or Troodos ophiolite(Fig.1c,d).Th in both dolerites deviate from the MORB array with negative slopes on the Th/Yb ***/Yb diagram(Fig.2a),suggesting constant subduction component added to the mantle source(Pearce et al.,1995).We chose depleted MORB source Mantle(DMM,Workman and Hart,2005)as the starting composition computing immobile element contents for primary melt