甘肃北山双峰山花岗闪长岩锆石LA-ICP-MS定年及其构造意义  

LA-ICP-MS zircon U-Pb ages of the granodiorites from Shuangfengshan in Beishan Mountain,Gansu Province,and its tectonic significance

作　　者：孙新春[1] 王怀涛[1] 李通国[1] 魏海峰[1] 徐磊 王晓伟[1] SUN Xin-chun;WANG Huai-tao;LI Tong-guo;WEI Hai-feng;XU Lei;WANG Xiao-wei(Geological Survey of Gansu Province,Lanzhou 730000,China)

机构地区：[1]甘肃省地质调查院,甘肃兰州730000

出　　处：《岩石矿物学杂志》2021年第2期171-184,共14页Acta Petrologica et Mineralogica

基　　金：2020年陇原青年创新创业人才项目(甘组通字[2020]9号);中国地质调查局项目(12120114014501)。

摘　　要：为了确定双峰山花岗闪长岩的形成时代、岩体成因及形成环境,对其开展了锆石U-Pb年代学、岩石地球化学以及Sr-Nd同位素的研究。LA-ICP-MS锆石U-Pb定年结果表明双峰山花岗闪长岩的形成时代为334.8±2.1 Ma(MSWD=1.2)。岩石具较高的SiO2(55.42%~65.53%)、Al2O3(14.84%~17.53%)和Na_(2)O+K_(2)O(7.42%~8.32%)含量,K_(2)O/Na_(2)O值为0.16~0.29,为钙碱性、准铝质Ⅰ型花岗岩。岩石富集Rb、K、Nd、Zr、Hf元素,相对亏损Nb、Ta、P、Sm、Ti元素。Nb/La值(0.41~1.01)、Hf/Th值(0.80~1.15)接近典型岛弧岩浆岩。(87Sr/86Sr)i值(0.7060~0.7095)和εNd(t)值(-0.22~+0.52)显示出壳幔相互作用的特点。结合区域地质研究表明,双峰山花岗闪长岩源于中元古代晚期形成的玄武质下地壳,是早石炭世玄武岩浆底侵作用下发生部分熔融的产物,形成于活动大陆边缘,是辉铜山-帐房山蛇绿岩所代表的弧后盆地北向俯冲的响应。Zircon U-Pb chronology,rock geochemistry and Sr-Nd isotope have been investigated in this paper to determine the formation time,genesis of rock and formation environment of the granodiorite in Shuangfengshan.The results show that the formation age of Shuangfengshan granodiorite is 334.8±2.1 Ma(MSWD=1.2).The rocks have relatively high SiO2(55.42%~65.53%),Na_(2) O+K_(2) O(7.42%~8.32%)and Al2 O3 values(14.84%~17.53%),as well as K_(2) O/Na_(2) O ratios(0.16~0.29),which indicates that they are calc-alkaline,quasi-aluminum I-type granite.The rocks are rich in Rb,K,Nd,Zr and Hf,and relatively deficient in Nb,Ta,P,Sm and Ti.Nb/La(0.41~1.01)and Hf/Th(0.80~1.15)ratios are close to the data of typical island arc magmatic rocks.(87 Sr/86Sr)i(0.7060~0.7095)andεNd(t)(-0.22~+0.52)show characteristics of crust-mantle interaction.Combined with regional geological research,the authors hold that Shuangfengshan granodiorite originated from the basaltic lower crust formed in the late Mesoproterozoic on the active continental margin under the underplating of Early Carboniferous basaltic magma,which was the response of the northward subduction of the back-arc basin represented by the Huitongshan-Zhangfangshan ophiolite.

关 键 词：花岗闪长岩 地球化学 俯冲作用 弧后盆地 北山 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]