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西藏西部普兰蛇绿岩中的MOR型辉长岩:岩石学和年代学
引用本文:刘钊,李源,熊发挥,吴迪,刘飞.西藏西部普兰蛇绿岩中的MOR型辉长岩:岩石学和年代学[J].岩石学报,2011,27(11):3269-3279.
作者姓名:刘钊  李源  熊发挥  吴迪  刘飞
作者单位:1. 中国地质大学地球科学与资源学院,北京100083;大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037
2. 大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037
3. 中国地质大学地球科学与资源学院,北京100083;滑铁卢大学地球科学学院,滑铁卢ON N2L3G1
基金项目:本文受国家自然科学基金重点项目(40930313)、国家行业专项(SinoProbe-05-02)和中国地质调查局工作项目(1212011121263、1212011121272)联合资助.
摘    要:西藏普兰蛇绿岩位于雅鲁藏布江缝合带的西段,主要由地幔橄榄岩、辉长岩和玄武岩组成.在拉昂错南侧有一个辉长岩体,面积约1 km2,与其相邻的地幔橄榄岩为侵入接触关系.辉长岩为中细粒辉长结构,块状构造,主要矿物为半自形板柱状基性斜长石和他形-半自形粒状辉石.岩石化学成分显示其具有MOR型岩石特点,表现为中等含量的TiO2(1%~1.77%),低含量的K2O(0.08%~0.21%)和P2O5(0.1%);轻稀土元素(LREE)轻微亏损的近平坦型稀土元素球粒陨石标准化模型,(La/Ce)N、(La/Sm)N和(La/Yb)N等特征比值分别为0.73~0.80、0.44~0.58、0.53~0.65;岩石的高场强元素(HFSE)为相互平行的具有接近1的平坦型分配型式.微量元素的N-MORB标准化图解显示富集大离子亲石元素(LILE)如Rb,高场强元素(HFSE)轻微亏损.辉长岩锆石的LA-ICP-MS U-Pb年龄为130±3Ma,指示了普兰蛇绿岩形成的时代,与邻区休古嘎布、东波蛇绿岩的形成时代相一致.

关 键 词:普兰蛇绿岩  N-MOR辉长岩  锆石  地球化学  西藏
收稿时间:7/5/2011 12:00:00 AM
修稿时间:2011/9/30 0:00:00

Petrology and geochronology of MOR gabbro in the Purang ophiolite of western Tibet, China.
LIU Zhao,LI Yuan,XIONG FaHui,WU Di and LIU Fei.Petrology and geochronology of MOR gabbro in the Purang ophiolite of western Tibet, China.[J].Acta Petrologica Sinica,2011,27(11):3269-3279.
Authors:LIU Zhao  LI Yuan  XIONG FaHui  WU Di and LIU Fei
Affiliation:School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;Earth Science Faculty, University of Waterloo, Waterloo ON N2L 3G1, Canada;State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract:The Purang ophiolite in the western part of the Yarlung Zangbo suture zone, is composed of mantle peridotite, gabbro and basalt. A gabbro massif, about 1km2 in area, occurs south of Lhanag-tso. The gabbro is fine- to medium-grained with a massive texture, and is composed mainly of subhedral tabular to prismatic plagioclase and anhedral to subhedral granular pyroxene. The gabbro has a MOR-type composition with relatively high TiO2 (1.00%~1.77%) and low K2O (0.08%~0.21%) and P2O5 (0.1%). It is characterized by having a nearly flat chondrite-normalized REE pattern with only slightly depleted LREE, as indicated by (La/Ce)N=0.73~0.80, (La/Sm)N=0.44~0.58 and (La/Yb)N=0.53~0.65. An N-MORB-normalized spider diagram shows enrichment in LILE (e.g., Rb) and slight depletion in HFSE. U-Pb dating of zircons from gabbro of the Purang ophiolite yields an age of 130±3Ma. This age is similar to that of the nearby Xiugugabu and Dongbo ophiolite, and is taken as the crystallization age of the Purang ophiolite.
Keywords:Purang ophiolites  N-MOR gabbro  Zircon  Geochemistry  Tibet
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