青藏高原羌塘中部香桃湖地区早二叠世双峰式火山岩的成因及其地质意义  

Petrogenesis and geological implications of Early Permian bimodal volcanic rocks in Xiangtaohu area,central Qiangtang,Tibetan Plateau

作　　者：贾人懿 董永胜[1] 许王 王鹏森[1] 陈卓 JIA Renyi;DONG Yongsheng;XU Wang;WANG Pengsen;CHEN Zhuo(College of Earth Sciences,Jilin University,Changchun 130061,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]吉林大学地球科学学院,长春130061 [2]中国地质科学院地质研究所,北京100037

出　　处：《世界地质》2022年第3期465-482,509,共19页World Geology

基　　金：国家自然科学基金项目(42002240);中国地质科学院地质研究所基本科研业务经费项目(J2002)联合资助。

摘　　要：青藏高原中部的南羌塘地块是了解冈瓦纳大陆裂解和劳亚大陆增生的关键地区。为进一步深入探讨南羌塘地块分离的动力来源,笔者对首次在香桃湖地区内展金组冰海杂砾岩段发现的一套双峰式火山岩(粗玄岩-安山岩组合)进行详细系统的锆石年代学和全岩地球化学研究。LA-ICP-MS锆石U-Pb定年结果表明:粗玄岩和安山岩的岩浆喷发时间分别为(290±2)Ma和(281±4)Ma,均形成于早二叠世。地球化学结果表明:粗玄岩属于亚碱性玄武岩,其TiO_(2)、FeO^(T)含量较高,轻重稀土元素分馏明显,微量元素组成类似于洋岛玄武岩;安山岩的主量元素组成明显不同于粗玄岩,以高SiO_(2)和Al_(2)O_(3)以及低MgO、TiO_(2)、FeO^(T)为特征,微量元素组成与前者相似,但更亏损Nb、Ta和Ti。进一步的地化特征研究显示粗玄岩和安山岩均具有大陆板内性质,前者是由地幔柱源区岩石部分熔融形成的原始熔体,经结晶分异作用形成;后者在形成过程中加入了大量地壳物质。香桃湖地区双峰式火山岩岩石成因和构造环境的研究,为地幔柱活动和俯冲洋壳拖拽共同导致早二叠世基梅里超级地体从冈瓦纳大陆北缘裂解并进一步打开新特提斯提供了新的证据。The southern Qiangtang block in the middle of the Qinghai-Tibet Plateau is a key area to understand the breakup of Gondwana and the accretion of Laurasia.In order to further explore the dynamic source of the separation of the southern Qiangtang block,this paper presents a detailed and systematic zircon chronology and whole-rock geochemistry study on a set of bimodal volcanic rocks assemblage(dolerite-andesite)discovered for the first time in the Zhanjin Formation in the Xiangtaohu area.The LA-ICP-MS zircon U-Pb data shows that the dolerite and andesite formed in the Early Permian,with magmatic eruption times of(290±2)Ma and(281±4)Ma,respectively.The geochemical results show that the coarse basalt belongs to subalkaline basalt and is characterized by high concentrations of TiO_(2) and FeO^(T).In addition,it has high LREEs/HREEs ratios,and the trace element composition is similar to that of ocean island basalt(OIB).In contrast,the andesite has different major element composition from that of dolerite.It has high SiO_(2) and Al_(2)O_(3) but low MgO,TiO_(2) and FeO^(T) contents.Although its trace element composition is similar to that of dolerite,it is more depleted in Nb,Ta and Ti.Further study of geochemical characteristics shows that both dolerite and andesite formed in an intracontinental setting.The dolerite originated from partial melting of enriched asthenospheric mantle source related to mantle plume and subsequently experienced extensive fractional crystallization.During the formation of the andesite,a large amount of crustal materials were added.Based on the petrogenesis and tectonic setting of bimodal volcanic rocks in the Xiangtaohu area,the mantle plume activity and the drag of subducted oceanic crust resulted in Early Permian rifting of the Cimmerian super-terrane from the northern margin of Gondwana and the subsequent opening of the Neo-Tethys Ocean were supported.

关 键 词：冈瓦纳裂解 早二叠世 青藏高原 南羌塘地体 双峰式火山岩 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]