松潘-甘孜造山带南部江浪穹隆中侏罗世花岗岩及构造意义  

Tectonic significance of Middle Jurassic granites in the Jianglang dome,southern Songpan-Ganzi orogen belt

作　　者：刘晓佳[1,2] 许志琴[3] LIU Xiaojia;XU Zhiqin(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences and Space Science,Peking University,Beijing 100871,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing,Jiangsu 210046,China)

机构地区：[1]自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]北京大学地球与空间科学学院,北京100871 [3]南京大学地球与工程学院,江苏南京210046

出　　处：《地质学报》2021年第6期1754-1773,共20页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号1212010818094)资助的成果。

摘　　要：新火山和乌拉溪花岗岩体侵位于松潘-甘孜造山带南部的江浪穹隆中,是理解松潘-甘孜造山带的构造演化的重要窗口。锆石U-Pb定年结果表明新火山和乌拉溪花岗岩体的结晶年龄为162±1~170±0.5Ma。岩体主要由石英、斜长石、钾长石和少量黑云母组成,具有低A/CNK(1.10~0.99)、TFeO/MgO(8.55~2.83)和K_(2)O/Na_(2)O(1.34~0.51),较低的Zr+Nb+Ce+Y浓度(平均258×10^(-6)),Al2O3、P2O5与SiO2呈负相关,相当于I型花岗岩的特征。一些主微量元素具有明显的关联性,说明在岩浆演化过程中发生了分离结晶(例如:角闪石和钛铁矿)。富集轻稀土和大离子亲石元素,亏损高场强元素,并具有较低的Mg#值(38.7~17.3)和Y/Nb值(0.45~0.16)以及多数为负的εHf(t)值(-24.8~-7.6),证明岩浆可能起源于古老地壳的部分熔融并受到幔源或者新生地壳熔融混染。松潘-甘孜地块的中侏罗世岩浆活动是在造山运动向陆内伸展这一构造体制转化背景下,由于地壳伸展造成了古老中基性地壳的部分熔融。The Xinhuoshan and Wulaxi granite plutons are located in the Jianglang dome,which is a key domain for providing deep insight into the tectonic evolution of the Songpan-Ganzi orogen.This study presents zircon U-Pb chronology,geochemistry and Hf isotope data to explore their petrogenesis and metallogenic implications.Zircon U-Pb dating provides crystallization ages of 162±1~170±0.5Ma for the Xinhuoshan granite and the Wulaxi granite.Both granites are composed chiefly of quartz,K-feldspar,plagioclase with minor biotite.They are characterized by low A/CNK(1.10~0.99),TFeO/MgO(8.55~2.83)and K_(2)O/Na_(2)O ratios(1.34~0.51)with low Zr+Nb+Ce+Y concentrations(average 258×10^(-6))and zircon saturation temperatures(781~651℃).Their Al2O3,P2O5and SiO2contents show negative correlations,and they thus fit the I-type granite definition.Some major and trace elements exhibit strong correlations,implying extensive fractional crystallization(e.g.,hornblende and ilmenite)during the magma evolution.Two granites show enrichment in light rare earth elements and large ion lithophile elements,and depletion in high field strength elements.They have low Mg#values(38.7~17.3)and Y/Nb ratios(0.45~0.16),and yield dominantly negativeεHf(t)values(-24.8~-7.6),indicating a heterogeneous source and their derivation from remelting of ancient continental crust(e.g.,Mesoproterozoic Liwu Group in this region)with minor juvenile crust or contaminated by the mantle materials.Combined with prior studies,we conclude that the Xinhuoshan and Wulaxi granites were formed in the Middle Jurassic magmatic activity.The structural transformation of collision orogeny and post collision extension resulted in the formation of the Middle Jurassic magma by partial melting caused by decompression.

关 键 词：松潘-甘孜造山带 I型花岗岩 伸展背景 江浪穹隆 

分 类 号：P534.52[天文地球—古生物学与地层学] P588.121[天文地球—地质学]