内蒙凉城2.0Ga变质花岗岩对超高温变质作用的制约  

Paleoproterozic 2.0Ga meta-granite in the Liangcheng area,Inner Mongolia:Constraint on regional ultra-high temperature metamorphism

作　　者：张华锋[1,2] 罗志波[1] 王浩铮[3] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]西北大学地质学系大陆动力学国家重点实验室,西安710069 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2013年第7期2391-2404,共14页Acta Petrologica Sinica

基　　金：973项目(2012CB416603);国家自然科学基金项目(40772122;41030316)联合资助

摘　　要：内蒙凉城位于华北克拉通北缘中段,孔兹岩带的东端。本区孔兹岩系内存在着大量的古元古代变质花岗岩,彼此呈构造接触。根据野外地质特征、岩石学和矿物学特征,可将其分为三类:Ⅰ)二长花岗岩;Ⅱ)深熔花岗岩;Ⅲ)似斑状紫苏花岗岩。本文针对Ⅰ类花岗岩进行详细的锆石和岩石成因研究。结果显示该类岩体形成于大约2.0Ga左右,并记录了1.95～1.90Ga的变质作用年龄,对应的岩浆和变质锆石结晶温度(采用锆石Ti温度计)分别为856～964℃(平均912℃)和861～900℃(平均879℃),暗示该花岗岩体源区曾经历了高温熔融事件,同时也说明它们与围岩孔兹岩共同经历了古元古代的超高温变质作用。该类型岩体的岩石化学特征类似太古宙TTG或Adakite,而深熔花岗岩类(Ⅱ类)的地球化学特征则类似岛弧岩浆岩。这种差异说明凉城2.0Ga变质花岗岩的原岩非孔兹岩重融而成的S型花岗岩。锆石Lu-Hf和全岩Nd同位素组成则指示形成岩体的物质主要来自新太古代和古元古代下地壳的熔融。The Liangcheng area is located in the central-north of the North China Craton （NCC）,easternmost portion of the khondalite belt,in which voluminous Paleoproterozoic meta-granites are exposed and can be divided into three groups of monzogranite （Ⅰ）,anatectic granite （Ⅱ） and charnockite（Ⅲ） in terms of geology and mineralogy.Our focus is on the Group Ⅰ which is dominated by mineral assemblages of plagioclase,K-feldspar,quartz,biotite,and garnet.In terms of mineral assemblages and geology,they are distinctive from the ca.1.93Ga anatectic granites （Group Ⅱ） which were generated by partial melting of the khondalite.LA-ICP-MS zircon U-Pb dating showed that the Group Ⅰ were emplaced approximately ～ 2.0Ga ago and metamorphosed at 1.95 ～ 1.90Ga ago,with magmatic zircons being crystallized at 856 ～ 964℃ （averaged 912℃） and 861 ～ 900℃ of the metamorphic zircons.The results indicate that the Liangcheng meta-granite （Group Ⅰ）,together with wall rocks of the khondalite series,were metamorphosed at 1.95 ～ 1.90Ga ago,under ultra-high temperature.In situ Lu-Hf isotopic compositions of zircon,integrated with whole rock Nd isotopes and geochemistry,suggest that the Liangcheng 2.0Ga meta-granite was not S-type granite and dominantly generated by partial melting of the Archean and Paleoproterozoic lower crust.

关 键 词：锆石U-PB定年 花岗岩 超高温变质作用 孔兹岩 华北克拉通 

分 类 号：P588.121[天文地球—岩石学]