西藏仁错地区前寒武纪基底对北拉萨地块起源的约束  

Constraints of Precambrian basement in Ren Co area, Tibet on the origin of the North Lhasa terrane

作　　者：胡培远[1] 翟庆国[1] 赵国春[2,3] 唐跃 杨宁[1] 李金勇 HU Pei-yuan;ZHAI Qing-guo;ZHAO Guo-chun;TANG Yue;YANG Ning;LI Jin-yong(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Department of Earth Sciences,University of Hong Kong,Hong Kong,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]香港大学地球科学系,中国香港 [3]大陆动力学国家重点实验室,西北大学地质学系,陕西西安710069

出　　处：《岩石矿物学杂志》2022年第2期281-302,共22页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(41872240,42072268)。

摘　　要：北拉萨地块是青藏高原前寒武纪岩石出露最为广泛的地区之一,该地块的新元古代演化历史及其在超大陆演化中所扮演的角色一直存有争议。围绕这一科学问题,本文收集整理了北拉萨地块仁错地区前寒武纪念青唐古拉岩群的同位素年代学、地球化学和同位素地球化学资料,从中发现了3期新元古代岩浆-沉积-变质记录,包括:(1) 925~886 Ma,岩石组合为MORB型变质基性岩和变质沉积岩,代表了大陆裂谷最晚期的胚胎洋壳和伴生沉积物;(2) 822~671 Ma,主要为斜长角闪岩和花岗片麻岩,原岩为拉斑玄武岩、钙碱性玄武岩、A2型花岗岩等,它们与同时代的角闪岩相变质记录共同形成于洋壳俯冲过程;(3) 658~646 Ma,包括中基性侵入岩和火山岩以及榴辉岩相-角闪岩相变质岩,它们共同记录了陆-陆碰撞环境下俯冲洋壳的断离过程。上述3期岩浆-沉积-变质记录与莫桑比克洋的演化时限一致,分别对应威尔逊旋回中的胚胎期、衰退期和终了期。此外,本文还通过念青唐古拉岩群中的埃迪卡拉纪岩浆记录进一步约束了冈瓦纳超大陆北缘“西早东晚”安第斯型岩浆弧的时空分布特征。综合本次研究和前人成果可知,北拉萨地块起源于非洲大陆,在新元古代早期从非洲大陆裂解出来,在新元古代中期经历了莫桑比克洋的消减-闭合过程,随后在新元古代晚期就位于东非造山带北段并且受到了冈瓦纳超大陆北缘安第斯型岩浆弧的影响。The North Lhasa terrane is one of the most widely exposed areas of Precambrian rocks in the Tibetan Plateau, but the Neoproterozoic tectonic evolution of the terrane and its role in the supercontinent evolution have been controversial. Focusing on this scientific problem, this paper collects and arranges the isotopic chronology, geochemistry and isotopic geochemistry data of the Precambrian Nyainqentanglha Group in Ren Co area of the North Lhasa terrane, and finds three periods of Neoproterozoic magmatic-sedimentary-metamorphic records:(1) 925 ~ 886 Ma, the rock association is MORB-type metamorphic basic rocks and metamorphic sedimentary rocks, representing the embryonic oceanic crust and associated sediments in the latest stage of continental rift;(2) 822 ~ 671 Ma, mainly plagioclase amphibolites and granitic gneisses,whose protoliths are tholeiites,calc-alkaline basalts and A2-type granite,which were formed in the process of oceanic subduction together with the coeval amphibolite-facies metamorphism;(3) 658 ~ 646 Ma,including intermediate-basic intrusive and volcanic rocks and eclogite-amphibolitefacies metamorphic rocks,which jointly record the process of slab break-off in a collision zone. The above three magmatic-sedimentary-metamorphic records are consistent with the evolution of the Mozambique Ocean,corresponding to the embryonic stage,decline stage and end stage of the Wilson cycle respectively. In addition,the temporalspatial distribution of Andean-type magmatism in the northern margin of Gondwana supercontinent are further constrained by the Ediacaran magmatic rocks in the Nyainqentanglha Group. Based on this study and previous results,we suggest that the North Lhasa terrane drifted away from Africa in the Tonian,experienced the subduction-collision processes of the Mozambique Ocean in the Cryogenian,and then located in the northern East African orogen in the Ediacaran,and influenced by the Andean-type magmatism along the Gondwanan Proto-Tethyan margin in the Ediacaran-Cambrian.

关 键 词：青藏高原 北拉萨地块 前寒武纪基底 地球化学 岩浆弧 

分 类 号：P597[天文地球—地球化学] P542[天文地球—地质学]