秦岭造山带光头山岩体群黑云母地球化学特征及成岩意义  

GEOCHEMISTRY OF BIOTITE AND ITS PETROGENESIS SIGNIFICANCE OF THE GUANGTOUSHAN GRANITE PLUTON GROUP,QINLING OROGEN

作　　者：张有军[1] 梁文天[2] 罗先熔[1] 董云鹏[2] 张国伟[2] 

机构地区：[1]广西隐伏金属矿产勘查重点实验室、桂林理工大学地球科学院,广西桂林541004 [2]大陆动力学国家重点实验室、西北大学地质学系,陕西西安710069

出　　处：《矿物岩石》2015年第1期100-108,共9页Mineralogy and Petrology

基　　金：教育部博士点基金新教师项目(20106101120006);国家自然科学基金(41002070);西北大学大陆动力学国家重点实验室科技部专项(BJ081331)

摘　　要：针对南秦岭光头山岩体群的岩相学和黑云母地球化学分析,进而对秦岭造山带晚三叠世花岗岩形成的温度、压力和氧逸度等物理化学条件进行专门的研究。其中岩相学观察表明,光头山岩体群主要由黑云母二长花岗岩和花岗闪长岩组成。电子探针分析结果表明黑云母二长岗岩中的黑云母是铁质黑云母,花岗闪长岩中的黑云母是镁质黑云母,所测黑云母的Fe2+/(Fe2++Mg)比值变化范围较小,表明其未受到后期改造,为原生黑云母,可以用来估算岩体的成岩物理化学条件。根据黑云母地球化学成分计算的成岩温度为(645~710)℃,压力为(126~309)MPa,logfo2为-12^-15,岩体侵位于中上地壳层次(约8.6km)。黑云母地球化学分析还表明,光头山岩体群主要为过铝质-造山带钙碱性花岗岩,岩浆以壳源为主兼具壳幔混源的特征。Temperature,pressure,oxygen fugacity and other physical and chemical conditions of the Late Triassic granite plutons in the Qinling orogen have been poorly studied.Research of petrography and geochemistry of biotite was carried out to solve this problem.Observations of petrography show that the Guantoushan pluton consists of biotite monzonitic granite and granodiorite.Electron microprobe analysis shows that the biotites in biotite monzonitic granite belong to Fe-biotites and the biotites in granodiorite belong to Mg-biotites.Their Fe2＋/（Fe2＋＋Mg）values are less extensive,indicating that biotites are protosomatic biotites.The diagenetic conditions can be estimated as the forming temperature,solidification pressure and logfo2 of granitic complex range from 645℃to 710℃,from 126 to 309,and from-15 MPa to-12 MPa,respectively.The Guangtoushan pluton was emplaced in the upper crust level（approximately 8.6km）.Geochemistry of biotite analysis also shows that the Guantoushan granitic complex is characterized by the peraluminous and orogenic calc-alkaline rocks and that magma mixing plays a great role in magma crystallization.

关 键 词：黑云母地球化学 地质温压计 氧逸度 晚三叠世花岗岩 秦岭造山带 

分 类 号：P619.221[天文地球—矿床学]