Abstract
Rb-Sr mineral isochron age was obtained for the unmetamorphozed granodiorite from a dike intruded into the Opirarukaomappu gabbroic complex, southern Hidaka metamorphic belt, Hokkaido, Japan. The isochron gives solidification age of 25.5 Ma with an initial Sr isotope ratio of 0.70362. The obtained age is obviously younger than inferred intensive metamorphic age of 56 Ma in the Hidaka metamorphic belt. The young solidification age is in accord with the other evidences. The hornblende geobarometer of the the granodiorite implied that it crystallized in a shallow crust. The granodiorite dike rocks have more evolved nature than the host diorite, but they are not co-magmatic.
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