西藏朗县蛇绿混杂岩中变辉绿岩和变玄武岩的年代学和地球化学  

Chronology and geochemistry on gabbro and basalt of the ophiolite mélange in Lang County,Tibet,China

作　　者：张万平[1,2] 莫宣学[1] 朱弟成[1] 袁四化 王立全 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]成都地质调查中心,成都610082

出　　处：《成都理工大学学报（自然科学版）》2011年第5期538-548,共11页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：国家重点基础研究发展规划项目(2009CB421003);国家自然科学基金资助项目(41073033;40830317);中国地质调查局基础调查计划项目(1212010610101)

摘　　要：对西藏雅鲁藏布缝合带东段朗县混杂岩中的辉绿岩和玄武岩进行了岩石学、地球化学和SHRIMP锆石年代学研究。在早侏罗世(大约191Ma B.P.)和侏罗纪最晚期到白垩纪最早期(大约146～148Ma B.P.)分别有2幕岩浆活动;侵入于191.4±3.7Ma B.P.的变辉绿岩,是迄今为止在雅鲁藏布蛇绿混杂岩带发现的最老的N-MORB型岩浆活动记录,这是新特提斯在早侏罗世以前就可能已经扩张产生的重要证据;具E-MORB地球化学特征的变辉绿岩侵入于147.2±3.4Ma B.P.,与兼具E-MORB和OIB地球化学特征的玄武岩同时侵位(145.7±2.5Ma B.P.和147.8±3.3Ma B.P.),暗示当时新特提斯洋内可能发生了重要的热点和洋脊相互作用;朗县蛇绿混杂岩晚期岩浆活动与雅鲁藏布混杂岩带南部错那地区的早期热点型岩浆活动(～145Ma B.P.)同期,意味着当时在新特提斯洋壳岩石圈及南部被动大陆边缘岩石圈之下,很可能存在彼此有成因联系的地幔柱或热点型岩浆活动。The authors discuss the geochemical characteristics and zircon U-Pb dating of the gabbro and basalt from the ophiolite complex in Lang County of the Yarlung Zangbo suture zone.The results show that（1） there were two episodes of magma activities in the earlier Jurassic period（about 191 Ma B.P.） and the earlier Cretaceous period（146~148 Ma B.P.）;（2） the age of one gabbro sample with geochemical characteristics of N-MORB type magma is 191.4±3.7 Ma B.P.,that is the earliest age of N-MORB type magma in the Yarlung Zangbo suture zone.This age provides an important evidence for the Tethyan overspreading before earlier Jurassic period;（3） the age of one gabbro sample with geochemical characteristics of E-MORB type magma is 147.2±3.4 Ma B.P.,and the age of two basalt samples with geochemical characteristics of E-MORB type magma and OIB type magma are 145.7±2.5 Ma B.P.and 147.8±3.3 Ma B.P.,these indicates the mutual actions between hot spots and middle ocean;（4） the characteristics that the magma activity period in Lang County is the same as the magma activity period in Cuona located in the southern Yarlung Zangbo suture zone imply that there are possibly hot spots and plumes（there is a genetic relationship between them） type magma activity under the lithosphere of Tethyan ocean crust.

关 键 词：SHRIMP锆石U-Pb法测定年龄 朗县蛇绿混杂岩 雅鲁藏布缝合带 西藏南部 

分 类 号：P588.124[天文地球—岩石学] P588.145[天文地球—地质学]