日高変成帯における花崗岩質マグマと壁岩の熱的および化学的相互作用  [in Japanese] Thermal and chemical interaction between granitic magmas and wall rocks in the Hidaka metamorphic belt, northem Japan  [in Japanese]

日高変成帯のSタイプ花崗岩と砂泥質変成岩との間に分布するミグマタイトについて、形成されたP-T条件の考察を行った。ミグマタイトには、花崗岩と変成岩との間の反応関係が見られ、母岩の変成度に対応して系統的に反応が異なっている。これらのミグマタイトは、角閃岩相低温部までのゾーンでは花崗岩マグマによる接触変成作用・交代作用により説明される。角閃岩相上部〜グラニュライト相のゾーンでは部分溶融反応と同化作用によって説明される。

The Hidaka Metamorphic Belt (HMB) is a low P/T type metamorphic belt, and represents a tilted crustal section of the Tertiary magmatic arc in central Hokkaido. The metamorphic grades are divided into four zones: I of greenschist facies, II of greenschist to lower amphibolite facies, III of upper amphibolite facies and IV of granulite facies. Large amounts of gabbro, diorite and granite are intruded into these metamorphic rocks. The granific rocks are tonalitic and granodioritic in composition and are mainly peraluminous (S-type) with less amounts of metaluminous (I-type) granitoids. All the granitic suites are syn-tectonic and syn-metamorphic intrusives. These granitic rocks are grouped into four depth type saccording to their intrusive metamorphic zones; (1) upper granite-granodiorite in zone I, (2) middle tonalite-granodiorite in zone I and II, (3) lower tonalite in zone III and (4) basal tonalite in zone IV. Each type of granitic rocks has a characteristic mineral assemblage that change gradually from deeper to shallow intrusive types. The primary tonalitic magma was generated by crustal anatexis in the deep crust, crystallized and differentiated with changing P-T conditions during the ascent resulted inproducing the depth series of granific rocks. various types of migmatite are developed between these granitic rocks and metamorphic country rocks. Inferred from the analysis of textural and chemical relations of minerals, and their P-T conditions of reactions, these migmatites were formed by contact metamorphism and metasomatism between the granitic magma and the wall rocks in the middle zones, and by anatexsis and assimilation in the lowerand basal zones.