Trace elements, Sr and Nd isotopic compositions of the Okushiri granodioritic body, southwest Hokkaido.

概要

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retaceous Okushiri granodioritic body occurred in Okushiri Island, southwest Hokkaido was studied its geochemical characteristics. This body consists mainly of hornblende biotite granodiorite with small amount of granite and aplite, and contains gabbroic xenoliths. The body shows characteristics of volcanic arc type granite based on Nb-Y and Rb-(Y+Nb) diagrams. Seven samples of granodiorite give a defined Rb-Sr whole rock isochron age of 104±16 Ma and initial Sr isotopic ratio of 0.70536±0.00033 (2σ) and two samples have negative initial εNd values. Obtained new data and previous reports suggest that Okushiri granodioritic body has geochemical and petrological characteristics of plutonic rocks from both belts of Kitakami and Abukuma. From trace and isotopic data it may be inferred that source magma of the Okushiri body was caused by partial melting of lower crust, or that derived from upper mantle or lower crust were affected by crustal materials.
日本鉱物科学会の論文