High-temperature metamorphism and the formation of migmatites

在“高温变质作用与混合岩的形成”这一题目下，我们的兴趣主要集中在各种岩石学方面，如矿物平衡、混合岩的产状和成因、压力-温度-时间演化、地壳深熔作用以及日本区域变质带(如日高、阿布库马、良田、日田和东高变质带)中S型花岗岩类岩浆的成因。我们的部分成果已经被报道了(例如，1992年《集结月刊》第5期和第11期的21篇论文)，但许多文章将陆续发表。由于篇幅所限，仅有以下几个重要结果：1.深熔混合岩普遍存在于高T、低P区域变质带的高温地段(如日达卡和东高)。泥质和镁铁质深熔岩的特征是存在具有振荡带状结构的自形斜长石，以及可归因于部分熔体分离的其他结构(例如，日达卡)。在最高温度部分，一些角闪岩含有脉体网络，其中的脉体化学成分从辉长岩到英云闪长岩再到奥长闪长岩，表明这些脉体与其寄主角闪岩分离，代表了部分熔融(如日达卡和阿布库马)的分异过程。S型英云闪长岩浆是在变质作用高峰期下地壳变质岩大量部分熔融形成的，泥质麻粒岩以闪锌矿形式存在。而一些S型英云闪长岩则是RESITE与部分熔体的混合体，是两者相互作用的产物(如东高和东高)。

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).