Geological and petrological studies of low-temperature metamorphic rocks in the northern Kitakami Mountains.

北上山北部低温变质岩的地质和岩石学研究。

• 批准号: 61540580
• 负责人: ONUKI Hitoshi
• 金额: $ 1.54万
• 依托单位: Hirosaki 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: 1986
• 资助国家: 日本
• 起止时间: 1986 至 1987
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-61540580/
• 关键词: Low Temperature And Pressure Metamorphism; パンペリー石-アクチノ閃石相と関連変成相; 低温・低圧広域変成岩; プレーナイト-パンペリー石相の関連変成相

The northern part of the Kitakami Mountains is composed mainly of late Paleozoic to late Mesozoic sedimentary rocks, which were mostly subjected to contact metamorphism by Cretaceous granitic intrusions. However, low-temperature regional metamorphic rocks have been found in separate fragmental areas unaffected by the later contact metamorphism.The typical low-temperature metamorphic remnants, the Kuzakai, Morioka, Manami-yamagata and Kuzumaki areas, in the "Hayachine Tectonic Belt" and North Kitakami Belt were studied in detal. In these areas the pumpellyite + actinolite association is commonly found in mafic rocks and the phengite + chlorite assemblage in pelitic rocks. Alkali-amphibole (not crossite but magnesioriebeckite) occurs only in the Kuzumaki area. In addition to chlorite, epidote and albite, metamorphic minerals such as prehnite, pumpellyite and stilpnomelane are widespread in mafic rocks. These minerals and mineral assemblages suggest that the pumpellyite-actinolite facies metamorphism took place in all the areas. The major metamorphic minerals mentioned above were analysed by means of an electron-probe microanalyser.On the other hand, lower Cretaceous formations (the Harachiyama Formation and its correlatives) are characterized by the prehnite + pumpwllyirw association. Actinolite occurs only in the biotite zone of the thermal aureole around the Cretaceous granitic intrusion. Therefore, they have suffered the prehnite-pumpellyite facies metamorphism.

北上山脉的北方部分主要由晚古生代至晚中生代沉积岩组成，这些沉积岩大多受到白垩纪花岗质侵入体的接触变质作用。本文对早川构造带和北北上构造带中的久坂海、盛冈、真见山形和久卷等典型的低温变质遗迹进行了详细的研究。在这些地区，镁铁质岩中常见绿柱石+阳起石组合，泥质岩中常见多硅白云母+阳起石组合。碱性角闪石（不是十字石，而是镁钠闪石）仅产于Kuzumaki地区。镁铁质岩石中除镁铁质、绿帘石和钠长石外，还广泛存在着普白石、绿帘石和硬钾长石等变质矿物。这些矿物和矿物组合表明，这些地区都发生过普钠闪石-阳起石相变质作用。用电子探针分析了上述主要变质矿物，下白垩统地层（原山组及其相关地层）以葡萄石+ pumpwllyirw组合为特征。阳起石仅产于白垩纪花岗岩体周围热晕的黑云母带中。因此，它们遭受了钠闪石-钠闪石相变质作用。