Activity of proto-Pacific superplume from the viewpoint of Paleozoic ophiolites in Southwest Japan.

点击翻译按钮获取中文摘要

1. Oe-yama ophiolite : Ashidachi complex shows the Sm-Nd isotopic ages of 560 Ma for coarse-grained gabbro, and 350 to 450Ma for the fine-grained gabbro.2. Yakuno ophiolite : Gneissose metagabbro shows the Sm-Nd isotopic ages from 340 to 38OMa. U-Pb dating for the zircon from two samples of tonarite in the Asago-cho area yield ages of 282 and 285Ma respectively. Gabbro migmatite was discovered from the Lower gabbro member in the Asago-cho area, at where the partial melting process was well documented at the base of immature island arc.3. Greenstones in the Jurassic accretionary complex : Greenstone of Masuda area shows the Sm-Nd isotopic ages of ca. 340Ma Alkaline basalt such as ankaramite was found from the greenstones in Mochigase-cho area, which shows very high Nb/Zr ratio that it was similar to HIMU basalt.4. Cphiolite of other areas : Age determinations using Sm-Nd, Rb-Sr isochron methodand the U-Pb for zircon by SHRIMP were carried out about the Schmidt Peninsula ophiolite of the northern Sakhalin, and the ages ca. 125Ma were obtained. Metamorphic facies and geochemical analysis were enforced about the Mariana forearc ophiolite, and a resemblance with the Yakuno ophiolite was found.5. construction of the geochemical data base : Data base system using "filemaker Pro ver. 3.O" was composed as a relational database for geochemistry.6. Summary : A coeval activities from 350 to 400Ma among Paleozoic ophiolitic rocks such as fine-grained gabbro and diabase intruded in the Ce-yama ophiolite, the sea mount group of the Akiyoshi terrane, the gneissose metagabbro of the Yakuno ophiolite, greenstones in the Jurassic accretionary complex are prominent in Southwest Japan. The simultaneous activities might be occurred to make superplume lasted from Devonian to early Carboniferous time in the proto-Pacific region.