北上山地の中・古生層:研究展望

概要

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Pre-Silurian basement of the Kitakami Mountains is now inferred as represented by forearc system on the oceanic crust. The said system was in front of an assumed continental land mass containing gneisses and orthoquartzite formation (e. g. Abukuma Mountains). The Hikami granite, at least a part ofit, might be the result of forearc igneous activity which was the beginning of a new arc system. The Palaeozoic formations from the Silurian onwards were formed as the result of backarc deposition. Thus the Southern Kitakami Mountains does not seem to represent an allochtonous terrane originated from the Pacific acontinent. The Hayachine Tectonic Zone was developed by obduction from the oceanic side on to the island arc of the Southern Kitakami Mountains in the Triassic (?) time. Accretionary prism since then was responsible for constructing the Northern Kitakami Mountains. Granitization following the Early Cretaceous volcanism formed the "continental" crust of the Kitakami Mountains. And we now see the relict of another forearc igneous activity (Oyashio Palaeoland) and forearc basin in the arc-trench gap off the Kitakami.
日本地質学会の論文
1985-03-30