南祁连化石沟花岗岩年代学、地球化学特征及其构造意义  

Geochronology and Geochemistry Characteristics of the Granites from the Huashigou Area, South Qilian and Their Tectonic Significance

作　　者：胡万龙 贾志磊[1,2] 王金荣[1] 侯克选 王淑华[1] HU Wanlong;JIA Zhilei;WANG Jinrong;HOU Kexuan;WANG Shuhua(Key Laboratory of Mineral Resources in Western China, School of Earth Sciences, Lanzhou University, Lanzhou 730000, China;Gansu Provincial Bureau of Geology and Mineral Exploration & Development, Lanzhou 730000, China)

机构地区：[1]甘肃省西部矿产资源重点实验室,兰州大学地质科学与矿产资源学院,兰州730000 [2]甘肃省地质矿产勘查开发局,兰州730000

出　　处：《高校地质学报》2016年第2期242-253,共12页Geological Journal of China Universities

基　　金：甘肃省2009年矿产资源补偿费项目甘肃省阿克塞县化石沟铜矿成矿条件及成矿远景预测(甘国土资勘发〔2009〕15号);中央高校基本科研业务费专项资金(lzujbky-2013-113)联合资助

摘　　要：化石沟二长花岗岩呈长条状侵入于泥盆系-石炭系阿木尼克组。岩石LA-ICP-MS锆石U-Pb加权平均年龄为252.0±2.1 Ma,形成于晚二叠世。岩石高SiO_2(69.8%~72.2%)、Al_2O_3(14.2%~15.4%),低的TiO_2、MgO含量(分别为0.28%~0.36%、0.60%~0.77%),A/CNK=1.08~1.14,富碱(Na_2O+K_2O=6.57%~8.00%);相对富集Th、K、Pb,亏损Nb、Ta、P、Ti,低Sr(201×10^(-6)~248×10^(-6),高Y(19.4×10^(-6)~24.0×10^(-6)),富集LREE,(La/Yb)N=10.8~18.4,中等负Eu异常(δEu=0.55~0.68);全岩(^(87)Sr/^(86)Sr)i为0.7060~0.7061,εNd(t)为1.63~1.84,εHf(t)=8.79。二长花岗岩的全岩Nd和Hf模式年龄分别为780~794 Ma和694 Ma。综合研究表明二长花岗岩是新元古代中期形成的玄武质下地壳在晚古生代晚期玄武质岩浆底侵加热作用下发生部分熔融的产物,形成于造山挤压向后造山伸展转变的构造环境。The monzonitic granites intruded into Devonian-Carboniferous Amunike formation in a long strip fashion in the Huashigouarea. According to the zircon U-Pb weighted mean age of 252.0 ± 2.1Ma determined using LA-ICP-MS, it was suggested that the rockwas formed in late Permian. Monzonitic granites contain rich SiO2 (69.8%~72.2%) and Al2O3 (14.2%~15.4%), and low TiO2, MgO(0.28%~0.36%, 0.60%~0.77%, respectively), with A/CNK=1.08~1.14, rich alkali (Na2O+K2O = 6.57%~8.00%), relatively enriched Th,K, Pb, depleted Nb, Ta, P and Ti, low content of Sr (201×10-6~248×10-6), high content of Y (19.4×10-6~24.0×10-6), enriched LREE, (La/Yb)N=10.8~18.4, moderate anomaly negative Eu (δEu=0.55~0.68); whole-rock (87Sr/86Sr)I=0.7060~0.7061, εNd(t)=1.63~1.84, and εHf(t)=8.79. The Nd and Hf model ages of whole-rock of monzonitic granites are 780~794 Ma and 694 Ma, respectively. Overall,our study shows that the Huashigou monzonitic granites is the product of partial melting of Mid-Neoproterozoic basaltic lower crust bythe underplating heating of late Paleozoic basaltic magma under the tectonic setting of orogenic compression transforming into postorogenic extension.

关 键 词：二长花岗岩 地球化学 晚二叠世 构造环境 化石沟 南祁连山 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学]