西藏日土早白垩世高镁流纹质岩石时代、地球化学特征及地质意义  

Geochronology,Geochemical Characteristics and Significance of High-Mg Rhyolite Rocks in Early Cretaceous in Ritu,Tibet

作　　者：张建珍 高莲凤 张振国 李广栋 范建军[3] 潘志龙 贠杰 李强 张涛 Zhang Jianzhen;Gao Lianfeng;Zhang Zhenguo;Li Guangdong;Fan Jianjun;Pan Zhilong;Yun Jie;Li Qiang;Zhang Tao(Hebei Institute of Regional Geological Survey,Langfang 065000,China;College of Mining Engineering,Liaoning Technical University,Furin 123000,China;College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]河北省区域地质调查院,河北廊坊065000 [2]辽宁工程技术大学矿业学院,辽宁阜新123000 [3]吉林大学地球科学学院,吉林长春130061

出　　处：《地球科学》2020年第8期2868-2881,共14页Earth Science

基　　金：国家自然科学基金项目(No.41972004);中国地质调查局项目(Nos.1212011221084,1212010711603);河北省自然科学基金项目(Nos.E2019209339,D2017209236)。

摘　　要：班公湖-怒江洋晚期的构造演化存在诸多争议.以在西藏日土东新发现的高镁流纹质岩石为研究对象,开展了年代学、地球化学等方面的研究.LA-ICP-MS锆石U-Pb测得样品113.69±0.82 Ma(MSWD=2.7)的谐和年龄,证明其为早白垩世晚期岩浆活动的产物.岩石地球化学分析显示,样品具有富硅(70.27%~75.72%)、高镁(3.50%~4.12%)、高Mg#(82.68~84.79)等特征.稀土元素呈现富集轻稀土、相对亏损重稀土(LaN/YbN=7.00~9.34),存在较为明显的Eu负异常(δEu=0.50~0.65);富集Th、U,亏损Ba、Sr、P和Ti等元素,微弱的Nb、Ta亏损.在构造环境判别图解上,样品落于陆缘弧区域,表明其形成于大洋岩石圈俯冲的构造背景.研究结果为沙木罗组海相地层的厘定提供了确切的同位素年龄,同时也为探讨班公湖-怒江洋白垩纪时期的构造演化提供了新的依据.There are still many controversies about the tectonic evolution of Bangongco-Nujiang suture zone in the late period.In this paper,it presents a study of chronology and geochemistry,taking the newly discovered high magnesium rhyolite in East Ritu of Tibet as the object.The concordance age of 113.69±0.82 Ma(MSWD=2.7)measured by LA-ICP-MS zircon U-Pb indicates that it is the product of magmatic activity in the late Early Cretaceous.The geochemical analyses show that the samples are rich in SiO2(70.27%-75.72%),MgO(3.50%-4.12%)and Mg#(82.68-84.79).It is relatively enriched in light rare earth elements,and depleted in heavy rare earth elements(LaN/YbN=7.00-9.34),with obvious negative Eu anomalies(δEu=0.50-0.65).The results show enrichment of Th,U,depletion of Ba,Sr,P and Ti,and weak depletion of Nb and Ta.In the diagram of tectonic environment discrimination,the samples are projected in the continental margin arc area,indicating that they were formed in the tectonic background of oceanic lithosphere subduction.This study provides a precise isotopic age to determine the marine strata of Shamulo,and new evidence for further studies on the structural evolution of the Bangongco-Nujiang suture zone in Cretaceous period.

关 键 词：西藏日土 高镁流纹质岩石 地球化学 锆石U-PB定年 班公湖-怒江结合带 

分 类 号：P736.22[天文地球—海洋地质]