We propose from our recent investigations that the Hidaka metamorphic belt is the junction of two tectonic units consisting of overturned oceanic crust slub in the western zone and of upthrust continental crust in the main zone.
In the western zone, there occur, from west to e a st, greenschists derived from basalts, epidote amphibolites from diabasic to gabbroic rocks, amphibolite to metagabbros from gabbros, metamorphosed layered gabbro-peridotite cumulates, and dunite-harzburgite tectonites. Complete ophiolite sequence with 5 Km in maximum thickness, although faulted, can be reconstructed in this zone. On the other hand, the main zone consists of, from west (stratigraphically lower) to east (upper), granulite zone, amphibolite zone, biotite, gneiss zone, biotite-muscovite gneiss to hornfels zone and nonmetamorphosed sediment (Hidaka group) zone. Spinel and plagioclase lherzolite masses derived from upper-mantle locally occur within the granulite zone. Various kinds of igneous rocks of island arc type such as olivine gabbro, hornblende gabbro, diorite and granite are intruded into selective horizons of the main zone. Total thickness of the main zone is 23 Km at maximum. The rock sequence of the main zone represents the cross-cut section of the continental type crust. The geothermal gradient estimated from the metamorphic conditions, nature of igneous rocks and the thickness of the crust section may indicate that the crust is an island arc type of initial stage of development.
抄録全体を表示