抄録
The Yurappu-dake plutonic complex in the central Oshima Peninsula can be divided into two series; a northern gabbroic body of 5 × 1km and a southern granodioritic body of 14 × 10km. The former consists of coarse gabbro, fine quartz gabbro, coarse quartz gabbro, fine tonalite, and porphyritic granodiorite, and the latter includes tonalite, granodiorite 1, granodiorite 2, and garnet bearing granite. Based upon the field observations, the following order of intrusion of this complex is proposed: 1) successive intrusions in the gabbroic body from early coarse gabbro to late porphyritic granodiorite, and 2) an intrusion of the main granodioritic body followed by a minor intrusion of the garnet bearing granite. The main granodioritic body shows continuous reverse zoning from two tonalitic cores to a felsic margin of the granodiorite 1 and 2. This reverse zoning appears to be the product of in situ crystal accumulation. Rapid solidification may have promoted to preserve the configuration of inward concentration of early-formed minerals due to magmatic convection. The gabbroic rocks and granodioritic ones exhibit continuous variation patterns in the bulk chemistry and mineralogy, indicating a close genetic relationship between the two rocks.
