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

1.Oe-Yama蛇绿岩：阿什达奇杂岩粗粒辉长岩的Sm-ND同位素年龄为560 Ma，细粒辉长岩的Sm-ND同位素年龄为350~450 Ma。雅库诺蛇绿岩：片麻质变质辉长岩的Sm-ND同位素年龄为340~380 Ma。Asago-Cho地区两个英云闪长岩样品的锆石U-Pb测年结果分别为282 Ma和285 Ma。辉长岩混合岩是在Asago-cho地区的下辉长岩段中发现的，在那里，未成熟岛弧底部的部分熔融过程得到了很好的记录。侏罗纪增生杂岩中的绿岩：Masuda地区的绿岩显示Sm-ND同位素年龄约为340 Ma，在莫赤沟地区的绿岩中发现了蓝晶石等碱性玄武岩，表明其Nb/Zr比值很高，与喜木玄武岩相似。其他地区的蛇绿岩：对库页岛北部施密特半岛蛇绿岩进行了Sm-ND、Rb-Sr等时线法年龄测定和SHRIMP锆石U-Pb测定，获得了125 Ma左右的年龄。对马里亚纳弧前蛇绿岩进行了变质相和地球化学分析，发现其与雅库诺蛇绿岩有相似之处。化探数据库的建立：利用“FileMaker Pro 3.0版”建立数据库系统，作为化探关系数据库。中山蛇绿岩中的细粒辉长岩、辉绿岩等古生代蛇绿岩、秋吉地体的海山群、雅库诺蛇绿岩的片麻质变质辉长岩、侏罗纪增生杂岩中的绿岩等350~400 Ma的同年活动在日本西南部较为突出。同时发生的活动可能使原太平洋地区的超羽从泥盆纪持续到石炭纪早期。

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.