广东南昆山A型花岗岩定年和环带云母研究  

Isotopic Dating and Origin of Complexly Zoned Micas for A-type Nankunshan Aluminous Granite

作　　者：刘昌实[1] 陈小明[1] 王汝成[1] 张文兰[1] 胡欢[1] 

机构地区：[1]南京大学地球科学系,南京大学内生金属矿床成矿作用国家重点实验室,210093

出　　处：《地质论评》2005年第2期193-200,i002,共9页Geological Review

基　　金：国家自然科学基金项目 (编号 40 13 2 0 10 ;40 0 73 0 0 9)资助成果。

摘　　要：广东南昆山 A型花岗岩出露面积约 2 0 0 km2 ,中粒等粒结构、块状构造 ,由铁叶云母、钠长石、微斜条纹长石和石英组成。弱过铝质 ,强亚碱质 ,富氟 (5 5 36× 1 0 - 6 ～ 90 5 4× 1 0 - 6 )贫氯 ,高的锆石饱和温度 (81 0～ 84 7℃ ) ,高 1 0 4 Ga/ Al比值 (4.37～ 7.2 6 )和高 Zr+Nb+Ce+Y含量 (45 0× 1 0 - 6 ～ 5 85× 1 0 - 6 )等 ,均与澳大利亚铝质 A型花岗岩相似。岩石内普遍发育环带云母 ,电子探针分析表明 ,复杂环带云母通常由若干黑云母条带 (铁叶云母 )和白云母条带组成 ,可识别出 3个构成部分 :核部带 ,幔部带和边部带。核部带形成于原岩浆处在深位时结晶的 ,幔部带形成于岩浆自深位快速上升到浅位时结晶的 ,而边部带形成在岩浆冷凝终结时。它们之间不同的边界形态说明了岩浆经历过铁钛氧化物的分离结晶作用、外来岩浆注入作用和去气作用等。环带云母是岩浆结晶历史的极好指纹。花岗岩锆石 U- Pb定年为 1 4 7± 0 .8Ma,应为中侏罗世—晚侏罗世侵入的。With an outcrop area of about 200 km2, the A-type Nankunshan aluminous granite is composed mainly of siderophyllite, albite plagioclase, perthitic microcline and quartz. The rock usually is weakly peraluminous and strongly subalkaline, carrying a high fluorine (5536×10 -6～9054×10 -6) content, a high 104Ga/Al ratio (4 37～7 26) and high (Zr+Nb+Ce+Y)(450×10 -6～585×10 -6) content. These features are particularly similar to those of the A-type aluminous granites in Australia. The granite frequently contains some amounts of zoned micas. Electron microprobe analyses show that the complexly zoned micas occurring in the Nankunshan granite are usually made of several biotite zones (siderophyllite) and muscovite zones. Three zoning parts in a complexly zoned mica grain can be distinguished: the core zone, the mantle zone and the rim zone. The core zone was formed during the period when primary magma was located in deep magma chambers. The mantle zone was crystallized during the period when magma arose to its shallow emplacement places from deep chambers. The rim zone was crystallized at the end of magma solidification. The distinct boundaries among them indicate that the magma from which the zoned micas may be formed underwent the following processes: crystallization fractionation of Fe-Ti oxides, the injecting process of external magma batches and degassing process etc. Grain zircon U-Pb dating shows that the Nankunshan granite was intruded in the middle Late Jurassic period (147±0.8 Ma).

关 键 词：南昆山 环带 定年 广东 铝质A型花岗岩 分离结晶作用 饱和温度 澳大利亚 电子探针 钛氧化物 去气作用 岩浆结晶 晚侏罗世 中侏罗世 钠长石 分析表 白云母 黑云母 组成 锆石 条带 核部 石英 岩石 上升 

分 类 号：P588.1[天文地球—岩石学]