柴北缘赛什腾地区早古生代岩浆活动与构造演化  

Early Paleozoic magmatism in the Saishiteng area, North Qaidam and their constraint on tectonic evolution

作　　者：王秉璋[1] 付长垒[2] 潘彤 李青[1] 逯永卓 金婷婷[1] WANG BingZhang;FU ChangLei;PAN Tong;LI Qing;LU YongZhuo;JIN TingTing(Key Laboratory of the Northern Qinghai-Tibet Plateau Geological Processes and Mineral Resources,Qinghai Geological Survey Institute,Xining 810012,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Bureau of Geological Exploration and Development of Qinghai Province,Xining 810001,China)

机构地区：[1]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,西宁810012 [2]中国地质科学院地质研究所,北京100037 [3]青海省地质矿产勘查开发局,西宁810001

出　　处：《岩石学报》2022年第9期2723-2742,共20页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(92062217);第二次青藏高原综合科学考察研究项目(2019QZKK0702);青海省地质矿产勘查开发局项目(青地矿[2021]61号)联合资助.

摘　　要：柴北缘赛什腾地区发育大量早古生代岩浆岩,记录了原特提斯洋演化的重要信息,对其研究有助于进一步认识秦祁昆增生和碰撞造山过程。本文报道了柴北缘赛什腾地区早-中奥陶世岩浆岩的锆石U-Pb年代学、锆石Lu-Hf同位素、全岩主微量元素地球化学及Sr-Nd同位素资料。早-中奥陶世岩浆岩主要包括花岗闪长岩、变辉绿岩和变辉长岩,LA-ICP-MS锆石U-Pb定年结果显示花岗闪长岩年龄是485Ma,变辉绿岩年龄是473Ma,变辉长岩年龄为470~464Ma。花岗闪长岩为弱过铝质钙碱性花岗岩类,轻重稀土分馏较强烈,La/Yb比值为18.0~25.1,(La/Yb)_(N)为12.9~18.0,Sr/Y比值(30.0~44.8)较高,Eu具轻度负异常,全岩ε_(Nd)(t)为+1.1~+3.4,初始^(87)Sr/^(86)Sr比值为0.7048~0.7060,锆石ε_(Hf)(t)为+9.4~+11.3。变辉绿岩为拉斑玄武岩系列,具有较高的MgO(5.31%~8.79%)含量和Mg^(#)值(47~58),其Al_(2)O_(3)和CaO含量分别为14.5%~18.07%和7.79%~11.92%,TiO_(2)含量(0.41%~0.83%)较低;此外,其稀土总量较低(26.0×10^(-6)~62.5×10^(-6)),轻重稀土分馏弱,(La/Yb)_(N)为3.3~4.0,基本不具Eu异常(δEu=0.9~1.1);全岩ε_(Nd)(t)为+2.2~+5.5,初始^(87)Sr/^(86)Sr比值为0.7049~0.7055,锆石ε_(Hf)(t)为+7.3~+9.1。变辉长岩为拉斑玄武岩系列岩类,富FeO^(T)(11.79%~15.45%)、低MgO(3.41%~5.23%)和Mg^(#)(31~44),TiO_(2)含量较高(介于1.06%~1.57%);其稀土总量较低(59.2×10^(-6)~121.6×10^(-6)),轻重稀土分馏弱,(La/Yb)_(N)为3.2~5.7,不具Eu异常(δEu=0.9~1.1);全岩ε_(Nd)(t)为+1.4~+1.9,初始^(87)Sr/^(86)Sr比值为0.7042~0.7044,锆石ε_(Hf)(t)为+7.5~+13.9。根据以上地球化学特征推断:花岗闪长岩源于有一定程度加厚的新生岛弧下地壳的部分熔融;而变辉长岩和变辉绿岩则源于亏损地幔楔,形成于俯冲相关的岩浆弧环境。结合以往研究成果,本文认为赛什腾地区早古生代主要存在~514Ma、485~464Ma、444~437Ma三期岩浆岩,形成于原特提斯洋洋内和陆缘俯冲(514~450Ma)以�Early Paleozoic magmatic rocks are widely distributed in the Saishiteng area of the North Qaidam,which not only recorded the evolution of the Proto-Tethyan Ocean but also provided important information for further understanding of the accretionary and collisional orogenic processes of the Qinling-Qilian-Kunlun orogens.In this paper,we report zircon U-Pb ages,zircon Lu-Hf isotopic data,whole rock major-and trace-element geochemistry and Sr-Nd isotopic data of a set of granidiorite,meta-dolerite and meta-gabbro from the Early to Middle Ordovician magmatic rocks in the Saishiteng area of the North Qaidam.LA-ICP-MS zircon U-Pb dating results show that the ages of granidiorite,meta-dolerite and meta-gabbro are 485Ma,473Ma and 470~464Ma,respectively.The granidiorites show similar geochemical features with the weakly peraluminous calc-alkaline type granite:they have a strong fractionation of the light rare earth elements(La/Yb=18.0~25.1;(La/Yb)_(N)=12.9~18.0)and high Sr/Y ratios(30.0~44.8)with slightly negative Eu anomalies;their whole-rockε_(Nd)(t)values and initial ^(87)Sr/^(86)Sr ratios varied within+1.1~+3.4 and 0.7048~0.7060,respectively;and the zirconε_(Hf)(t)values of the measured samples ranged in+9.4~+11.3.The meta-dolerites belong to the tholeiitic series,and they have high MgO(5.31%~8.79%),Al_(2)O_(3)(14.5%~18.07%)and CaO(7.79%~11.92%)contents,Mg^(#)values(47~58),and low TiO_(2) contents(0.41%~0.83%)and rare earth elements(26.0×10^(-6)~62.5×10^(-6))with a weak fractionation of the light rare earth elements((La/Yb)_(N)=3.3~4.0);they also have negligible Eu anomalies(δEu=0.9~1.1);the whole-rockε_(Nd)(t)values and initial ^(87)Sr/^(86)Sr ratios of them varied within+2.2~+5.5 and 0.7049~0.7055,respectively;and the zirconε_(Hf)(t)values of of the measured samples varied within+7.3~+9.1.The meta-gabbros belong to the tholeiitic series,and they have high FeO^(T)(11.79%~15.45%)and TiO_(2)(1.06%~1.57%)contents,and low MgO(3.41%~5.23%),Mg^(#)values(31~44),and total rare earth elements(59.2×10^(-6)~121.6×10^(-6

关 键 词：早古生代 岩浆活动 构造演化 赛什腾 柴北缘 

分 类 号：P588.12[天文地球—岩石学] P597.3[天文地球—地质学]