南岭东段强过铝质花岗岩中白云母研究  

Strongly Peraluminous Granites in Eastern Nanling Mountains,China:Study on Muscovites

作　　者：孙涛[1] 陈培荣[1] 周新民[1] 王汝成[2] 王志成[1] 

机构地区：[1]南京大学地球科学系,210093 [2]南京大学内生金属矿床成矿机制研究国家重点实验室,210093

出　　处：《地质论评》2002年第5期518-525,共8页Geological Review

基　　金：国家自然科学基金项目(编号 40072025);国家自然科学基金重点项目(编号 40132010)

摘　　要：根据显微镜下观察和电子探针成分分析,南岭东段赣南和粤北5个强过铝质花岗岩中存在两类白云母,即原生白云母和次生白云母。原生白云母呈自形—半自形,端面清晰,未被其他矿物包裹;低Fe/(Fe+Mg)值(<0.75,原子数比)和富Ti(原子数≥0.05)、Na(原子数≥0.10)、Mg(原子数≥0.10)、Al(原子数≥5.20)。次生白云母一般表现为他形、端面不清晰,也可由其他矿物(如黑云母、斜长石)变化而来,说明它形成于亚固相条件;其成分为高Fe(Fe+Mg)值和贫Ti、Na、Mg、Al,由此反映了花岗岩残余岩浆的成分特点。因此,多数次生白云母是岩浆后期—后岩浆期的晚世代白云母,或与岩浆体系有关的水热白云母。根据白云母形成条件和形成过程的讨论,以及研究的5个岩体的同位素地质年龄值(337～155Ma),推测赣南和粤北的强过铝质白云母花岗岩很可能是海西—印支运动挤压—逆冲作用使地壳增厚,诱发地壳深熔岩浆上侵结晶形成的;而且这一增厚—深熔—岩浆上侵的过程延续到燕山早期。因此,上述大的时代跨度的强过铝质花岗岩的存在标志着华南是特提斯构造域与太平洋构造域的衔接区。Based upon optical observation and electron microprobe analyses, the primary and secondary muscovites which were sampled from five strongly peraluminous granite bodies in the eastern Nanling Mountains, chemically and morphologically were distinguished. The primary ones in these bodies are cleanly terminated, ideally with euhedral form, and are not included by other minerals. They have low Fe/(Fe + Mg) (<0. 75, atomic ratio) and higher Ti (≥0. 5) , Na (≥0. 1) , Mg (≥0. 1) , Al (≥5. 2). The secpndary ones seem to be uncleanly terminated with anhedred form, and are altered from other minerals (e. g. biotite, plagioclase) showing a forming condition of subsolidus. Chemically they have higher Fe/(Fe + Mg), and are poor in Ti, Na, Mg, and Al reflecting the compositional characters of granitic residual magma. According to the discussion on forming condition and course of the two types of muscovites, and the isotope ages of the five granites, it is likely implied that the strongly peraluminous granites were formed through the crystallization of crust anatexis magma after the compression and overthrust accompaning with thickening of crust in Hercynian and Indosinian. This process continued to the Early of Yanshan Orogeny. It is believed that the presence of these strongly peralumnous granites formed during long time span indicates that the eastern Nanling is the joint of the Tethyan and the Pacific tectonic domaims.

关 键 词：强过铝质花岗岩 白云母 显微镜 电子探针 同位素地质年龄 特提斯构造域 太平洋构造域 

分 类 号：P578[天文地球—矿物学]