南昆仑结合带盲矿西沟早白垩世高分异花岗岩的发现及其地质意义  

Discovery of Early Cretaceous Highly Fractionated Granite in the Mangkuangxigou Area of South Kunlun Suture Zone and its Geological Significance

作　　者：逯永卓 王泰山[1] 余福承[1] 韩杰[1] 林艳海[1] 张鑫利[1] 李积清[1] 袁博武 徐贝贝[1] LU Yongzhuo;WANG Taishan;YU Fucheng;HAN Jie;LIN Yanhai;ZHANG Xinli;LI Jiqing;YUAN Bowu;XU Beibei(Qinghai Geological Survey Institute,Key Laboratory of the Northern Qinghai-Tibet Plateau Geological Processes and Mineral Resources,Xining 810012,Qinghai,China)

机构地区：[1]青海省地质调查院、青海省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

出　　处：《大地构造与成矿学》2023年第1期233-247,共15页Geotectonica et Metallogenia

基　　金：科技部第二次青藏高原综合科学考察研究项目(2019QZKK0702);青海省地质勘查基金项目(青国土资[2017]151);青海省地质矿产勘查开发局项目(青地矿科[2022]32号)联合资助。

摘　　要：为了研究南昆仑结合带早白垩世岩浆岩的成因类型和构造背景,本文对盲矿西沟一带出露的花岗岩开展岩相学、年代学和全岩地球化学研究。研究显示,盲矿西沟花岗岩的LA-ICP-MS锆石U-Pb年龄为113.4±0.6 Ma~117.5±1.5 Ma,形成于早白垩世。花岗岩含电气石、白云母等矿物,具有富硅(SiO_(2)=72.03%~75.10%)、富碱(K_(2)O+Na_(2)O=7.62%~7.86%)、过铝质(A/CNK=1.20~1.24),贫镁(MgO=0.13%~0.56%)、贫钛(TiO_(2)=0.08%~0.30%)的特征,为强过铝质高钾钙碱性-钙碱性系列;同时,富集Rb、Th、U等微量元素和相对亏损Ba、Sr、Ti元素;稀土元素总量较低,显现轻稀土元素富集、重稀土元素亏损的特征,具明显Eu负异常(δEu=0.18~0.31);SiO_(2)与TiO_(2)、Fe_(2)O_(3) T、MgO、Al_(2)O_(3)及Th与Rb元素均呈负相关,显现高分异S型花岗岩的特征。花岗岩岩浆源自局部伸展构造背景下幔源岩浆底侵加热引起的地壳物质部分熔融,是新特提斯班怒洋盆闭合在青藏高原北部引起的一种远程效应,并具有形成一期重要的钨锡成矿事件的可能性。In order to explore the petrogenesis and tectonic settings of the Early Cretaceous magmatic rocks in the South Kunlun Suture Zone,we systematically analyzed the petrography,geochronology,and whole-rock geochemistry of the granites in the Mangkuangxigou area.The Mangkuangxigou granites are featured by presence of tourmaline and mica in the rocks and formed at 113.4 to 117.5 Ma based on the zircon LA-ICP-MS U-Pb dating results.These granites have high contents of SiO_(2)(72.03%to 75.10%)and alkali(Na_(2)O+K_(2)O=7.62%to 7.86%),but low contents of MgO(0.13%to 0.56%)and TiO_(2)(0.08%to 0.30%),and belong to strongly peraluminous(A/CNK=1.20 to 1.24)and high-K calc-alkaline to calc-alkaline series.Meanwhile,these rocks are rich in Rb,Th and U,but depleted in Ba,Sr and Ti.They have low REE concentrations and show relatively enriched LREE and significant negative Eu anomalies(δEu=0.18 to 0.31).The SiO_(2) contents of the granites are negatively correlated with that of TiO_(2),Fe_(2)O_(3) T,MgO,Al_(2)O_(3),Th,and Rb,defining their affinities to highly fractionated S-type granites.Generation of the Mangkuangxigou granites was related to the partial melting of crustal rocks caused by underplating of mantle-derived magmas in an extensional setting.Such magmatism in the northern Tibetan Plateau was a far-reaching response caused by the closure of the Neo-Tethys Bangonghu-Nujiang Ocean,which may associate with a great W-Sn mineralization potential.

关 键 词：南昆仑 盲矿西沟 早白垩世 高分异S型花岗岩 新特提斯班怒洋 

分 类 号：P588[天文地球—岩石学] P597.3[天文地球—地质学]