High-temperature metamorphism and the formation of migmatites

在“高温变质作用和混合岩的形成”的题目下，我们的兴趣主要涉及岩石学的各个方面，如矿物平衡、混合岩的产状和成因、压力-温度-时间演化、地壳深熔作用和日本区域变质带中S型花岗岩类岩浆的起源（例如，日高、阿武熊、辽、希达和日后变质带）。我们的一部分结果已经报告（例如，21篇论文，1992年《月刊Chikyu》第5期和第11期），但许多文章将陆续发表。由于篇幅所限，本文只对几个重要结果进行了描述：1.原地熔融的深熔混合岩常见于高温低磷区域变质带的高温部位（如，日高和Higo）。泥质和镁铁质正长岩的特征是存在具有振荡带状结构的自形斜长石和归因于部分熔体偏析的其他结构（例如，日高）。在温度最高的部分，一些斜长角闪岩含有脉的网络，其中脉的整体化学成分从辉长岩到英云闪长岩到奥长花岗岩，这表明这些脉与它们的寄主斜长角闪岩分离，代表了部分熔体的分异过程（例如，日高和Abukuma）。S型英云闪长质岩浆是在变质高峰期下地壳变细岩大范围部分熔融，留下泥质麻粒岩作为残余岩而形成的。然而，一些S型英云闪长岩是残余岩与部分熔体的混合物，是两者相互作用的产物（例如，日高和Higo）。

Under the title "High-temperature metamorphism and the formation of migmatites", our interest was chiefly concerned with various petrological aspects such as mineral equilibria, the occurrence and genesses of migmatites, pressure-temperature-time evolution, crustal anatexis and the origin of S-type granitoid magmas in regional metamorphic belts of Japan (e.g., the Hidaka, Abukuma, Ryoke, Hida and Higo metamorphic belts). A part of our results were already reported (e.g., twenty-one papers in Nos. 5 and 11 of "Monthly Chikyu", 1992), but many articles will be published successively. Because of space limitation, only a few important results are described as follows:1. Anatectic migmatites melted in situ are common in the high temperature parts of high-T and low-P regional metamorphic belts (e.g., Hidaka and Higo). Pelitic and mafic anatexites are characterized by the presence of idiomorphic plagioclase with oscillatory zonal structure and of other textures attributed to segregation of the partial melt (e.g., Hidaka).2. In the highest temperature part, some amphibolites contain a network of veins in which the bulk chemistry of veins varies from gabbro through tonalite to trondhjemite, suggesting that these veins were segregated from their host amphibolites and represented a differentiation process of the partial melt (e.g., Hidaka and Abukuma).3. S-type tonalitic magmas were produced by the extensive partial melting of metapelites in the lower crust during the peak of metamorphism, leaving pelitic granulites as a restite. Some S-type tonalites, however, were admixtures of restite with the partial melt and were products of interaction between the two (e.g., Hidaka and Higo).