东昆仑东段三叠纪岩浆岩Nd-Hf同位素组分特征、物源演变规律及其构造背景  

Nd-Hf Isotopic Characteristics,Evolution Trend and Tectonic Setting of Triassic Magmatic Rocks in the Eastern Segment of East Kunlun Orogeny

作　　者：任海东 王涛[3] 潘彤 王建国[1] REN Haidong;WANG Tao;PAN Tong;WANG Jianguo(Department of Geological Engineering,Qinghai University,Xining 810016,Qinghai,China;Key Laboratory of the Northern Qinghai-Tibet Plateau Geological Process and Mineral Resources,Qinghai Geological Survey Institute,Xining 810012,Qinghai,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Bureau of Geological Exploration and Development of Qinghai Province,Xining 810001,Qinghai,China)

机构地区：[1]青海大学地质工程系,青海西宁810016 [2]青海省地质调查院,青藏高原北部地质过程与矿产资源重点实验室,青海西宁810012 [3]中国地质科学院地质研究所,北京100037 [4]青海省地质矿产勘查开发局,青海西宁810001

出　　处：《西北地质》2023年第6期95-112,共18页Northwestern Geology

基　　金：中国博士后科学基金“东昆仑东段三叠纪花岗岩源区演变特征及其成矿制约”(2019M663959XB);青海省地质矿产勘查开发局项目“东昆仑东段三叠纪花岗岩源区演变特征及其成矿制约”(青地矿[2019]8号);自然资源部深地动力学重点实验室开放课题“东昆仑-西秦岭造山带对接处共和盆地两侧三叠纪花岗岩物源演变特征和基底属性对比”(J1901-19)联合资助。

摘　　要：作为中央造山系西段的重要组成部分,东昆仑造山带以大面积区域性展布的三叠纪岩浆岩为鲜明特色。依据收集的东昆仑东段三叠纪岩浆岩96件锆石U-Pb年代学数据,限定三叠纪岩浆作用时间为252~212Ma。结合岩石组合,将其进一步划分为早(252~238Ma)、中(238~226 Ma)、晚(226~212Ma)3期,其中岩浆活动峰值为早期(252~238Ma)。Nd同位素数据(106件)统计结果表明:东昆仑东段三叠纪岩浆岩εNd(t)值为-9.4~-1.7,大多为-6.5~-3.0;Nd模式年龄TDM(Nd)为0.72~1.88 Ga,大多为1.00~1.80 Ga。Hf同位素数据(全岩、锆石;41件)统计结果表明:东昆仑东段三叠纪岩浆岩εHf(t)值变化较大(-8.4~+12.4),主要为-4.5~+2.0;地壳模式年龄TDMC(Hf)值为0.49~1.80 Ga,大多为1.15~1.55 Ga。整体而言,三叠纪岩浆岩物源以中元古代壳源物质的再造为主,新生地壳(<1.0 Ga)和古元古代地壳有所参与,但比例小。从岩浆活动早期(252~238Ma)到中期(238~226Ma)再到晚期(226~212Ma),εNd(t)值在岩浆活动早期(特别是在早三叠世)较高,正的εHf(t)值占据很大比例,物源中存在较多的新生物质;中期以较低的εNd(t)值和负的εHf(t)值为主,Hf模式年龄显示出现古元古代物质;晚期Nd-Hf模式年龄揭示较古老的壳源组分增多。这种岩浆岩物源演变趋势,与东昆仑东段三叠纪具俯冲到同碰撞再到碰撞后的构造演化背景一致。As a major component of the western segment of the Central Orogenic System,the East Kunlun Orogeny is characterized by the largely exposed of Triassic magmatic rocks.Based on the collected zircon U-Pb geochronological data of 96 Triassic magmatic rocks in the eastern segment of the East Kunlun orogeny,the Triassic magmatic activity is limited to 212~252 Ma,and can be further divided into three stages:early-(238~252 Ma),middle-(226~238 Ma)and late-stage(212~226 Ma).Among them,the peak magmatic period is the early stage(238~252 Ma).The statistical results of 106 Nd isotopes of Triassic magmatite in the eastern segment of the East Kunlun Orogeny show thatεNd(t)values range from-9.4 to-1.7,mainly concentrated between-6.5 and-3.0,and the Nd model ages(TDM(Nd))range from 0.72 to 1.88 Ga,mainly concentrated between 1.00 and 1.80 Ga.The statistical results of 41 Hf isotopes(whole rock,zircon)of Triassic magmatite show thatεHf(t)values vary greatly(-8.4 to+12.4),mainly concentrated between-4.5 and+2.0,and the crustal model ages(TDMC(Hf))range from 0.49 to 1.80 Ga,mainly concentrated between 1.15 and 1.55 Ga.Overall,the Triassic magmatic rocks are mainly derived from the reworking of Mesoproterozoic crustal materials,with minor involvement of juvenile crust(<1.0 Ga)and Paleoproterozoic crustal materials.From the early stage(237~250 Ma)to middle stage(226~238 Ma)and then to late stage(212~226 Ma),the Nd-Hf isotopic parameters seems exhibit a certain evolutionary trend.In the early stage especially in the early Triassic,theεNd(t)values are higher,and positiveεHf(t)values occupy a large proportion,indicating the presence of more juvenile material in the source.In the middle stage,lowerεNd(t)values and negativeεHf(t)values dominate the major proportion,and Hf model ages(TDMC(Hf))reveals the presence of Paleoproterozoic crustal material.In the late stage,the Nd-Hf model ages reveal an increase in older crustal source components.This magmatic source evolutionary trend is consistent with the tectonic evolution setting of su

关 键 词：岩浆岩 锆石年代学 Nd-Hf同位素 新生地壳 东昆仑东段 

分 类 号：P597[天文地球—地球化学]