Petrology, Geochemistry, and Tectonics of Tertiary Igneous Rocks from the Hidaka Belt, Central Hokkaido

第三纪日高岩浆活动发生在北海道中部一条长约300 km的带状岩浆带内。日高岩浆活动包括拉斑玄武岩层状橄榄辉长岩、不均一钙碱性辉长岩、I型和S型花岗岩。拉斑质盘克努希层状辉长岩侵入体、钙碱性Memurodake非均质岩体和原始Chiroro变粗粒岩的地球化学研究表明，它们来自N-MORB。因此，日高岩浆活动很容易解释为正常的海脊岩浆活动侵入陆源沉积物。我们可以认为扩张脊俯冲到增生棱柱之下和/或陆源沉积物在扩张脊上沉积。我们还发现了来自日高带的冰洲岩。它们的主量元素组成与沿着扩张脊的分异MORB不同，而与沿沿着或靠近扩张脊的热点上的拉斑质安山岩相似。例如，在一个实施例中，产于加拉帕戈斯群岛和冰岛的安山岩。

Tertiary Hidaka magmatism occurred in a meridional zone extending for about 300 km in Central Hokkaido. The Hidaka magmatism includes tholeiitic layered olivine gabbro, heterogeneous calc-alkaline gabbro-diorite, and I- and S-type granites. Geochemical investigations of the tholeiitic Pankenushi layered gabbroic intrusion, calcalkaline Memurodake heterogeneous pluton, and primitive Chiroro meta-dolerite indicate that they were derived from N-MORB. Therefore Hidaka magmatism is easily explained as normal ridge magmatism intruding into terrigenous sediments. We can assume that the subduction of spreading ridge beneath accretion prism and/or sedimentation of terrigenous sediment on the spreading ridge.We also found icelanditic rocks from the Hidaka belt. They are not similar in major element composition to the differentiated MORB occurred along the spreading ridge but to the tholeiitic andesite occurred on the hotspot along or near spreading ridge, e. g., andesitic rocks from the Galapagos Islands and Iceland.