恒山地区古元古代2.1Ga地壳重熔事件：钾质花岗岩锆石U-Pb定年及Hf-Nd同位素研究  

2.1Ga crustal remelting event in Hengshan Complex: Evidence from zircon U-Pb dating and Hf-Nd isotopic study on potassic granites

作　　者：赵瑞幅[1] 郭敬辉[1] 彭澎[1] 刘富[1] 

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029

出　　处：《岩石学报》2011年第6期1607-1623,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40730315、41023009);岩石圈演化国家重点实验室项目联合资助

摘　　要：恒山高级片麻岩地体位于华北克拉通中部构造带,主体是形成于晚太古代～2.5Ga的TTG片麻岩和少量变质火山沉积岩,并且经历了古元古代末～1.85Ga的高级变质作用。近年来,在恒山片麻岩地体中识别出一套钾质花岗岩小侵入体群,主要岩性是角闪石二长花岗岩和黑云母二长花岗岩。本文针对这套花岗岩,采用LA-ICP-MS和Cameca1280型离子探针进行锆石U-Pb定年,获得角闪石二长花岗岩岩浆锆石谐和年龄2052±17Ma和2084±4Ma,黑云母二长花岗岩岩浆锆石谐和年龄2060±18Ma和2083±15Ma。它们在误差范围内一致,代表花岗岩的形成时代。花岗岩锆石Hf同位素和全岩Nd同位素亏损地幔模式年龄分别为2.48～2.60Ga和2.43～2.68Ga,与围岩TTG片麻岩模式年龄范围基本一致。εHf(t)和εNd(t)主要分布范围分别为-6.0～0.6和-3.3～-1.7,未显示同期幔源物质的添加。据此可以推断,这些钾质花岗岩是恒山晚太古代TTG岩石在～2.1Ga部分熔融的产物。该期岩浆活动在华北克拉通已识别出多处,恒山地区的这期岩浆活动显示了地壳重熔特征。结合五台、阜平等地对于同期事件的研究,我们推测这些区域上～2.1Ga的岩浆活动形成于拉张裂解环境中。The Hengshan Complex in the Central Zone of the North China Craton,which is a typical high-grade terrain and experienced 1.85Ga high-pressure granulite facies metamorphism,composes of ~2.5Ga TTG gneisses and some paragneisses.A suite of potassic granites in this complex is investigated,which mainly consists of hornblende monzogranitie and biotite monzogranite.Zircon grains from a hornblende monzogranite sample yield a weighted average 207Pb/206Pb age of 2052±17Ma by LA-ICP-MS and 2084±4Ma by SIMS.A biotite monzogranite sample gives a weighted average 207Pb/206Pb age of 2060±18Ma by LA-ICP-MS and 2083±15Ma by SIMS.Ca.2080Ma SIMS ages possibly indicate the crystallization time of these potassic granites.εHf（t） values of zircons in the granites range from -6.0 to 0.6 with tDM （depleted mantle model ages） of 2.48~2.60Ga,while εNd（t） values range from -3.3 to -1.7 with tDM of 2.43~2.68Ga.These indicate that the potassic granites were likely derived from ancient crust.Together with the geochemical characteristics of the surrounding TTG rocks,we suggest that the ~2.1Ga potassic granites could be originated from the partial melting of the 2.5Ga TTG gneisses.This study confirms a Paleoproterozoic （~2.1Ga） crust remelting event in Hengshan Complex,which may occur in an extensional setting in the North China Craton.

关 键 词：钾质花岗岩 地壳重熔 古元古代 恒山杂岩 华北克拉通 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]