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Petrological Study on Continental Lower Crustal Materials.

大陆下地壳物质的岩石学研究。

基本信息

批准号：
01540653
负责人：
ARIMA Makoto
金额：
$ 1.34万
依托单位：
Yokohama National University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

Aims of this study are to understand petrological and chemical features of lower parts of continental crust and to evaluate chemical changes in the lower crust associated with granulite facies metamorphism and partial melting processes. This study particularly focuses on the processes related to formation of granulite facies metasedimentary rocks under lower crustal conditions. The main results of this study can be summarized as follows ;1. Metamorphic conditions, age, spatial distribution are determined for granulite facies metasedimentary rocks of lower crustal origin occurring in Labrador, Canada. Peak metamorphic condition of 1000^ﾟC and 10 kbar are estimated on the basis of mineral parageneses of the rocks. Osumilite, sapphirine, and other metamorphic minerals were formed in metasedimentary rocks by contact metamorphism associated with an emplacement of anorthositic magma under lower crust conditions. This is fifth metamorphic osumilite occurrence ever reported. Geochemical characteristics of the metasedimentary rocks suggest that partial melting and consequent melt segragation are important processes resulting in chemical modification of the lower crustal matireals.2. High pressure and temperature experiments were done to determine the stability relationship of osumilite in pelitic compositions under lower crustal conditions. The results suggest that osumilite is stable lower crustal phase as high as 12 kbar at 1000^ﾟC.3. This study clearly demonstrates that granulite facies metamorphism and crustal anatexis are closely related processes. Extremely low water activity in granulites would be caused by partial melting and melt segregation processes. It is most likely that parts of the continental lower crust is restite origin which is probably related to granitic magma generation.

本研究的目的是了解下地壳岩石学和化学特征，并评估与麻粒岩相变质和部分熔融过程有关的下地壳化学变化。本研究特别着重于下地壳条件下麻粒岩相变质沉积岩的形成过程。本研究的主要结果可以概括如下：1.确定了加拿大拉布拉多下地壳麻粒岩相变质沉积岩的变质条件、时代和空间分布。根据岩石的矿物共生关系，估计其峰值变质条件为1000 ℃和10kbar。在下地壳条件下，斜长岩浆侵位伴随着接触变质作用，在变质沉积岩中形成了硅镁石、硅镁石和其他变质矿物。这是第五次变质Osumilite发生有史以来的报道。变质沉积岩的地球化学特征表明，部分熔融和随后的熔融分凝作用是导致下地壳物质化学改性的重要过程.通过高温高压实验，研究了下地壳条件下泥质组分中硅镁石的稳定性关系。结果表明，在1000^oC时，在12kbar压力下，奥苏利岩是稳定的下地壳相.研究表明麻粒岩相变质作用与地壳深熔作用密切相关。麻粒岩中极低的水活度是由部分熔融和熔融分凝过程造成的。部分大陆下地壳可能为残余岩成因，可能与花岗质岩浆的生成有关。