华北地台部分麻粒岩地体及包体的地球化学特征对比  

Geochemical Comparative Studies of Some Granulite Terranes and Granulite Xenoliths from North China Craton

作　　者：黄小龙[1] 徐义刚[1] 储雪蕾[2] 张鸿祥[2] 刘丛强[3] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640 [2]中国科学院地质与地球物理研究所,北京100029 [3]中国科学院地球化学研究所,贵州贵阳550002

出　　处：《岩石矿物学杂志》2001年第3期318-328,共11页Acta Petrologica et Mineralogica

基　　金：国家攀登计划预选项目资助 (95 -预 - 39);国家杰出青年基金资助项目 (4 992 5 30 8)

摘　　要：华北地台麻粒岩包体 (汉诺坝 )与麻粒岩地体 (西望山、蔓菁沟 )存在明显的岩石地球化学特征差异 ,麻粒岩包体总体成分偏基性 ,麻粒岩地体总体成分偏长英质。形成时间、空间及构造背景的不同是造成成分差异的重要因素。汉诺坝麻粒岩包体是在拉张环境下玄武质岩浆底侵下地壳后结晶分异过程中堆晶作用的结果 ,其主、微量元素成分受控于辉石和斜长石堆晶的相对比例 ;下地壳物质的混染作用不是造成麻粒岩包体Nb、Ta、Th、U亏损的惟一因素 ,底侵的玄武质岩浆可能发生了含钛矿物相的结晶分离 ,造成了汉诺坝麻粒岩包体Nb、Ta亏损 ,而下地壳的麻粒岩相变质作用则使Th、U发生亏损。麻粒岩地体存在两种不同性质的微量元素组成 ,反映了两种不同构造环境的并置 。There are marked differences in petrogeochemistry between granulite xenoliths (Hannuoba) and granulite terranes (Xiwangshan and Manjinggou) in North China craton. The xenoliths are predominantly mafic in composition, whereas the terranes tend to be felsic in composition. Different epochs of rock formation, different depths of origin and different tectonic settings seem to be responsible for their diversities. Hannuoba granulite xenoliths are cumulates of the basaltic melts underplated in the lower crust associated with the extensional tectonics, and the geochemical compositions of the xenoliths are controlled by the proportion of pyroxene to plagioclase. The crustal contamination is not the only reason for Nb, Ta, U and Th depletion of Hannuoba granulite xenoliths. The basaltic melts might have experienced some fractional crystallization of Ti_minerals, which caused the Nb, Ta depletion, whereas metamorphism of granulite facies in the lower crust resulted in the depletion of Th and U in xenoliths. There exists the juxtaposition of different tectonics corresponding to the differences in geochemical composition of granulite terranes, which results from the extrusion uplift.

关 键 词：麻粒岩包体麻粒岩地体 堆晶 汉诺坝 华北地台 地球化学特征 

分 类 号：P588.34[天文地球—岩石学] P59[天文地球—地质学]