中山大学学报自然科学版 ›› 2018, Vol. 57 ›› Issue (6): 29-40.doi: 10.13471/j.cnki.acta.snus.2018.06.004

• 论文 • 上一篇    下一篇

西藏雅鲁藏布江蛇绿岩带中西段萨嘎蛇绿岩及其构造意义

赵佳楠   

  1. 广东省核工业地质局二九一大队,广东 广州 510800
  • 收稿日期:2017-11-29 出版日期:2018-11-25 发布日期:2018-11-25

Petro-geochemistry & chronology of Saga ophiolite in mid-western  part of Yarlung-Zangbo ophiolite belt and its tectonic significance

ZHAO Jianan   

  1. Guangdong Province Nuclear Industry Geological Bureau 291 Brigade, Guangzhou 510800, China
  • Received:2017-11-29 Online:2018-11-25 Published:2018-11-25

摘要:

基于萨嘎蛇绿岩序列中超基性岩和基性岩地球化学、岩石学、年代学、大地构造与地球动力学的数据资料,对西藏雅鲁藏布江蛇绿岩带中西段萨嘎蛇绿岩进行构造意义分析,认为萨嘎蛇绿岩层序中辉长岩属钙碱性-低钾拉斑玄武岩;蛇绿岩层序中的玄武岩为钙碱性玄武岩和碱性玄武岩,萨嘎蛇绿岩北亚带东侧热嘎、松多处玄武岩为钙碱性-低钾拉斑玄武岩,中西侧萨嘎处玄武岩为碱性-钾玄系列玄武岩。萨嘎蛇绿岩中基性岩具有大洋中脊、低钾拉斑玄武岩和碱性玄武岩特征。热嘎基性岩具有MORB微量元素特征,属大洋中脊玄武岩型;萨拉基性岩具有MORB和大洋岛弧玄武岩特征,属碱性玄武岩和低钾拉斑玄武岩型;松多基性岩具有MORB和大洋岛弧玄武岩特征,属地幔柱玄武岩和碱性玄武岩型。综上所述,位于北亚带萨嘎蛇绿岩多源,普遍贫Cr、Ti、Mn,微量元素具有地幔地球化学特征。在萨嘎蛇绿岩中发现大面积碱性玄武岩,其为后期混染壳源物质后产生,保留了幔源玄武质岩浆的部分地球化学特征,贫硅富碱,形成富碱矿物。萨嘎蛇绿岩达吉岭-萨拉剖面中辉长岩的锆石UPb年龄为1256±27 Ma,与整个雅鲁藏布江蛇绿岩中西段基性岩年龄(130~120 Ma)一致。推断萨嘎蛇绿岩可能形成于洋内超俯冲带(SSZ),并经历了后期弧前盆地洋中脊扩张改造,属洋内超俯冲带(SSZ)的弧前-弧-弧后环境。

关键词: 雅鲁藏布江蛇绿岩带, 萨嘎蛇绿岩, 岩石地球化学, 年代学, 构造意义, 洋内超俯冲带

Abstract:

Saga ophiolite from the mid-western part of the Yarlung-Zangbo ophiolite belt was researched in this paper. The data of petrogeochemistry, geochronology, chronology, geotectonics and geodynamics indicate that gabbro in Saga ophiolite was originated from calc-alkaline low-potassium tholeiitic basalt. The basalt in Saga ophiolite is calc-alkaline and alkali. The basalts in Rega and Songduo section line are calc-alkaline low-potassium tholeiitic basalts. The basite in Saga ophiolite has the same geochemical characteristics as MORB, tholeiitic and alkaline basalt. In summary, the Saga ophiolite in the northern sub-belt was originated from various multiple resources. It is generally depleted in Cr, Ti, Mn. The geochemical characteristics of trace elements are similar to mantle. A large area of alkaline basalt was found in the saga ophiolite, retaining geochemical characteristics of mantle with enriching alkali. Zircon U-Pb age of the gabbro in Dajiling-Sala profile is 125.6±2.7 Ma, in accordance with the basaltic age (130 to 120 Ma) in western Yarlung-Zangbo ophiolite. It is inferred that the Saga ophiolite is possible to form in the intra-oceanic supra-subduction zone (SSZ), suffering from expansion in mid-oceanic ridge situated in the forearc basin.

Key words: Yarlung-Zangbo ophiolite belt, Saga ophiolite, petro-geochemistry, geochronology, tectonic significance, SSZ

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