东昆仑造山带东段志留纪-泥盆纪中性岩的成因及其构造意义  

Petrogenesis and Tectonic Implications of Silurian to Devonian Intermediate Rocks from East Part of East Kunlun Orogenic Belt

作　　者：刘彬[1,2] 伍炼华 马昌前[2,3] 徐雨 李福林 湛君明 黄坚[3] 孙洋[1] Liu Bin;Wu Lianhua;Ma Changqian;Xu Yu;Li Fulin;Zhan Junming;Huang Jian;Sun Yang(School of Geosciences,Yangtze University,Wuhan 430100,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;Wuhan Center,China Geological Survey(Central South China Innovation Center for Geosciences),Wuhan 430205,China)

机构地区：[1]长江大学地球科学学院,湖北武汉430100 [2]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074 [3]中国地质大学地球科学学院,湖北武汉430074 [4]中国地质调查局武汉地质调查中心(中南地质科技创新中心),湖北武汉430205

出　　处：《地球科学》2023年第6期2398-2414,共17页Earth Science

基　　金：国家自然科学基金项目(Nos.42130309,41972066,41502050);中国地质调查局项目(Nos.12120115026901,1212011121270).

摘　　要：细致地调查与研究同折返或后碰撞岩浆岩能为理解大陆深俯冲-折返中的壳-幔相互作用及恢复碰撞造山带构造演化历史提供非常关键的线索.以东昆仑东段巴隆-金水口地区晚志留世-泥盆纪同折返期中性岩类为研究对象,开展锆石U⁃Pb年代学、岩石学、地球化学和同位素地质学等综合研究,以期为深入认识东昆仑造山带同折返期岩浆形成机制及其始特提斯洋构造演化提供新的证据.结果显示,巴隆和金水口地区中性岩的锆石U⁃Pb年龄分别为420 Ma和405 Ma,与东昆仑地区榴辉岩的折返时限重叠.其中,巴隆闪长玢岩具有相对低的MgO、Mg#以及相对高的K2O,而金水口闪长岩则具有相对高的MgO、Mg#以及相对高的Na2O.巴隆闪长玢岩的Nb/La比值随着Mg#降低而降低,符合同化混染与分离结晶作用(assimilation and fractional crystallization,AFC)的成分演化趋势,并且样品在La/Sm-La图解中投影均落在分离结晶演化曲线上.但是金水口闪长岩的Nb/La比值与Mg#之间不存在线性正相关关系,样品在La/Sm-La图解中投影均落在部分熔融曲线上.此外,与金水口闪长岩相比,巴隆闪长玢岩具有相对高的Isr值和相对低的εNd(t)值,并且显示更高的初始岩浆熔体温度.综合本文岩石学和地球化学等研究成果,可以确定巴隆和金水口地区两套中性岩的形成分别与玄武质岩浆的分离结晶与地壳混染、下地壳玄武质岩石的部分熔融有关.结合区域上已报道的最新研究资料,可以判断,这些中性岩类应形成于碰撞后伸展的环境中,板片断离很可能是触发东昆仑晚志留世-泥盆纪大规模同折返期岩浆活动关键因素.东昆仑地区至少从440 Ma开始进入大陆碰撞及陆壳深俯冲阶段.Investigations and studies on syn-exhumation or post-collisional magmatic rocks can provide key clues to understanding the crust-mantle interactions during the continental subduction and exhumation,and the tectonic evolution of collisional orogenic belts.In this paper it presents a comprehensive research of zircon U-Pb geochronology,petrology,geochemistry and isotopic geology for the syn-exhumation intermediate rocks in the east part of the East Kunlun orogenic belt.And the data could offer new insights into the generation of the syn-exhumation magmatism and the proto-Tethyan tectonic evolution.The results reveal that the Balong and Jinshuikou intermediate rocks yield zircon U-Pb ages of 420 Ma and 405 Ma,respectively,which overlap the exhumation timing of eclogites.The Balong diorite-porphyrite samples have relatively low MgO and Mg#with high K2O,while the Jinshuikou diorite samples have relatively high MgO and Mg#with high Na2O.The Balong diorite-porphyrite samples exhibit decreasing ratios of Nb/La with decreasing Mg#,similar to the features of assimilation and fractional crystallization(AFC).And all of them are plotted on the curve of fractional crystallization.However,the Jinshuikou diorite samples do not show positive correlation between Nb/La and Mg#,and those samples are plotted on the curve of partial melting.In addition,the Balong dioriteporphyrite samples have relatively higher Isr ratios and lowerεNd(t)values than those of the Jinshuikou diorite samples.Based on the new petrological,geochemical and isotopic compositions,it concludes that the Balong diorite-porphyrite and the Jinshuikou diorite were respectively derived from basaltic magma differentiation and contamination,and partial melting of the lower crustal basaltic rocks.Combining with new regional studies,it proposes that those intermediate rocks might be formed in a post-collisional extension environment,and slab break-off is the critical factor for triggering the Silurian to Devonian syn-exhumation magmatism.The continental collision and the

关 键 词：中性岩 陆壳折返 志留纪-泥盆纪 始特提斯 东昆仑造山带 岩石学. 

分 类 号：P581[天文地球—岩石学]