东昆仑中泥盆世A型花岗岩的确定及其构造意义  

Discovery of the Middle Devonian A-type Granite from the Eastern Kunlun Orogen and Its Tectonic Implications

作　　者：刘彬[1,2] 马昌前[1,2] 郭盼[2] 张金阳[3] 熊富浩[1,2] 黄坚[2] 蒋红安[2] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074 [2]中国地质大学地球科学学院,湖北武汉430074 [3]中国地质大学资源学院,湖北武汉430074

出　　处：《地球科学（中国地质大学学报）》2013年第5期947-962,共16页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.41272079);中国地质调查局计划项目(Nos.1212011121270;1212010918002);教育部和国家外国专家局高等学校学科创新引智计划(No.B07039)

摘　　要：东昆仑中泥盆世冰沟正长花岗岩具有高硅（SiO2含量为71.85%~72.77%）和高碱（K2O＋Na2O值为8.39~8.58）、相对富铝（A/CNK为0.93~1.03）、高FeOt/MgO（6.24~7.86）和104 Ga/Al值（3.04~3.60）、富集轻稀土、明显的Eu负异常、相对原始地幔明显富集Zr、Ga、Y和Hf等高场强元素并强烈亏损Ba、Sr、P和Ti元素的特征,这些特征与A型花岗岩类的地球化学特征一致.采用锆石LA-ICP-MS U-Pb法获得206Pb/238 U值加权平均年龄为391±3Ma（MSWD值为2.36）,表明该岩体为中泥盆世岩浆活动的产物.综合全岩Sr-Nd同位素、地球化学及实验岩石学等资料,可以判断该岩石为造山后伸展阶段长英质地壳物质（变杂砂岩）在低压高温氧化条件下发生部分熔融的产物.冰沟正长花岗岩是目前东昆仑地区报道的时代最晚的古生代A型花岗岩,它的出现可能标志着中泥盆世时期东昆仑始特提斯构造演化的彻底终结和古特提斯构造演化的崭新开始.Middle Devonian Binggou granites from the eastern Kunlun orogen,are characterized by relatively high silicon（SiO2 =71.85%-72.77%）,total alkali（K2 O＋Na2 O=8.39-8.58）,aluminum（A/CNK=0.93-1.03）,FeOt /MgO（6.247.86）and 104 Ga/Al values（3.04-3.60）,high LREE,obvious negative Eu anomalies,and notable enrichment of HFSE（Zr,Ga,Y,Hf,etc.）,strong depletion of Ba,Sr,P and Ti relative to the primitive mantle,similar to the geochemical features of A-type granites.The LA-ICP-MS Zircon U-Pb analyses yield a weighted mean 206Pb/238 U age of 391±3Ma（MSWD=2.36）,considered to be the formation age of the Binggou granites.With a comprehensive consideration on many different indexes,such as whole rock Sr-Nd isotopes,geochemistry,experimental petrology and so on,we conclude that the Binggou granites formed by partial melting of crust materials（meta-greywacke）on the conditions of low pressure and high temperature at the stage of postorogenic stretch.The Binggou granites are younger than the other Paleozoic A-type granites reported in the eastern Kunlun orogen,suggesting the ending proto-tethys and the beginning paleo-tethys.

关 键 词：A型 花岗岩 造山后 中泥盆世 东昆仑 构造 岩石学 

分 类 号：P581[天文地球—岩石学]