摘要
西藏尼木地区分布一套增生杂岩,其对冈底斯火山岩浆弧的演化具有重要意义。本文对该套增生杂岩中的变质火山岩的地质特征、矿物学、全岩地球化学和锆石U-Pb年代学等方面进行了综合研究。变质火山岩以斜长角闪岩、角闪斜长片麻岩为主,其中,角闪石主要为镁质角闪石,共生的斜长石主要为拉长石;变质火山岩经历了高温-中压变质作用;岩石富Al 2 O 3和贫TiO 2,弱富集轻稀土元素(LREE),富集Rb、Sr、Ba等大离子亲石元素(LILE),亏损Nb、Ta、Ti等高场强元素(HFSE),其地球化学特征与火山弧玄武岩的地球化学特征相似,其形成的构造环境为洋内岛弧或活动大陆边缘弧;岩浆锆石U-Pb年龄值为151.4±1.6Ma和150.7±1.4Ma,表明岩石的形成时代为晚侏罗世。综合研究认为,增生杂岩中的变质火山岩是新特提斯洋在晚侏罗世北向俯冲的产物,在陆-陆碰撞之前卷入增生系统,该套变质火山岩不是以往所认为的变质结晶基底。
Located in the south of the Gangdise magmatic arc,Nimu area occurred a set of metamorphic volcanic rocks mainly composed of amphibolite and amphibole-bearing plagioclase gneiss.Previously,they are believed to be the late Paleozoic crystalline basement rocks of the Lhasa block.By detailed geological survey and studies on mineral associations,geochemistry,and zircon U-Pb dating,the authors believe these metamorphic volcanic rocks were the accretion complex related to the subduction of the New Tethys Ocean in the late Jurassic.Following their formation,these arc-type volcanic rocks then experienced the mid-pressure amphibolite facies metamorphism in the late Cretaceous and the high-temperature contact metamorphism in the Eocene.Mineral chemistry shows that hornblendes in the rocks are mainly magnesium hornblendes and the paragenetic feldspars are mainly labradorites.The geochemistry of the rocks shows that Al 2 O 3 is in rich and TiO 2 is in poor,and LILEs such as Rb,Sr,Ba are in rich and HFSEs such as Nb,Ta,Ti are in poor,comparatively.The LA-ICP-MS U-Pb dating of zircons from the metamorphic volcanic rocks shows an age from 151.4±1.6Ma to 150.7±1.4Ma,which indicate that the studied rocks are originally the product of the northward subduction of the New Tethys Ocean in the late Jurassic.
作者
唐华
胡林
魏龙
陈永东
欧珠建层
周鹏
TANG Hua;HU Lin;WEI Long;CHEN Yong-dong;OU Zhu-jian-ceng;ZHOU Peng(Northwestern Sichuan Geological Team,Bureau of Geology and Mineral Resources Exploration and Development of Sichuan Province,Mianyang 621000,Sichuan,China;Geothermal and Geological Party,Bureau of Mineral Resource Exploration and Development of Tibet,Lhasa 850000,Tibet,China)
出处
《沉积与特提斯地质》
CAS
CSCD
2020年第2期104-115,共12页
Sedimentary Geology and Tethyan Geology
基金
中国地质调查局“西藏尼木地区1∶5万区域地质调查项目(项目编号:121201010000150014-07)”资助。
