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杨胜标,李源,杨经绥,李瑞保,董天赐,裴磊. 2017. 西藏日喀则白马让蛇绿岩:亚洲大陆边缘的小洋盆. 岩石学报, 33(12): 3766-3782
西藏日喀则白马让蛇绿岩:亚洲大陆边缘的小洋盆
作者单位E-mail
杨胜标 中国地质大学地球科学与资源学院, 北京 100083
中国地质科学院地质研究所地幔研究中心, 北京 100037 
 
李源 中国地质科学院地质研究所地幔研究中心, 北京 100037 liyuancags@126.com 
杨经绥 中国地质科学院地质研究所地幔研究中心, 北京 100037  
李瑞保 长安大学地球科学与资源学院, 西安 710054  
董天赐 中国地质大学地球科学与资源学院, 北京 100083  
裴磊 长安大学地球科学与资源学院, 西安 710054  
基金项目:本文受中国地质调查局项目(DD20160023-04)、国家重点研发计划(2016YFC0600310)和中国地质科学院基本科研业务费项目(J1617)联合资助.
摘要:
      藏南雅鲁藏布蛇绿岩被认为是新特提斯大洋岩石圈的残留。该带中段的日喀则白马让蛇绿岩是保存较完整的蛇绿岩岩块之一。该蛇绿岩主要由橄榄岩、蛇纹岩、镁铁质侵入岩和玄武岩组成,缺堆晶岩系。镁铁质侵入岩主要呈辉绿岩脉、岩床和少量的岩墙产出。辉绿岩脉在整个蛇绿岩层序中均有分布,侵入橄榄岩的部分岩脉已经变为变辉绿岩和异剥钙榴岩。辉绿岩床(墙)向上逐渐过渡为玄武岩。局部可见日喀则群整合覆盖在玄武岩之上。地球化学分析显示不同产状的镁铁质岩均属于低钾或中钾的拉斑玄武岩,亏损Nb、Ta、Ti和LREE,具有弧前玄武岩(FAB)或弧后盆地玄武岩(BABB)的特征,它们的Ti/V和Yb/V的比值与BABB或正常大洋中脊玄武岩(N-MORB)相似,Sr-Nd-Pb同位素数据指示了亏损地幔(DM)与富集地幔(EM)过渡的源区。镁铁质岩野外产出关系和地球化学特征表明,白马让蛇绿岩的镁铁质岩组合可能形成于SSZ环境。考虑到超镁铁质岩、镁铁质岩和日喀则群在空间上的连续性,认为白马让蛇绿岩可能是起源于亚洲大陆边缘俯冲带上的洋盆,属于原地系统,而非外来的构造岩片。
英文摘要:
      Yarlung Zangbo ophiolites in southern Tibet is considered as relics of the Neo-Tethyan oceanic lithosphere. The Baimarang ophiolite located in Xigaze, the middle section of the Yarlung Zangbo Suture Zone (YZSZ), is one of the best-preserved massifs. The ophiolite is scarcity of cumulate, and mainly includes peridotites, serpentines, mafic intrusions and basalts. Mafic intrusions in the Baimarang massif are mainly comprised of diabase dikes, sills and minor sheeted dikes. Diabase dikes are distributed in the whole ophiolite sequence and some of them invaded in peridotites had been altered into metadiabases or/and rodingites. Diabase sills gradually develop upward into basalts. Basalts conformably overlain by the Xigaze Group were observed in local areas. Geochemical analysis indicates that mafic rocks with different occurrences all belong to low-K and/or medium-K tholeiites, they characterized by depleted in Nb, Ta and LREE, which are similar to back-arc-basin basalts (BABBs) or fore-arc basalts (FABs). Their Ti/V ratios and Yb/V ratios are in accordance with BABBs and mid-ocean ridge basalts (N-MORB) and their Sr-Nd-Pb isotopic data shows a mantle source characterized by depleted mantle (DM) involvement of enriched component. Outcrops and petrogeochemistry indicate the Baimarang mafic rocks should be derived from supra-subduction zone (SSZ) setting. Given the spatial continuity among ultramafic rocks, mafic rocks and the Xigaze Group, we suggest that the Baimarang ophiolite is likely to origin form an ocean basin close to the Asian continental margin and probably belongs to autochthonous system rather than exotic tectonic blocks.
关键词:雅鲁藏布缝合带  日喀则蛇绿岩  构造环境  大陆边缘
投稿时间:2017-05-10  修订日期:2017-10-05
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