Effects of ridge subduction along the Japan margin -- an example of the Late Cretaceous-Paleogene

以下是本文所取得的研究成果.至少在日高带中有三排含原地绿岩的地层。地球化学特征表明，至少有一些原地绿岩类似于扩张脊产生的镁铁质熔岩。对日高变质带中的火成岩进行了地球化学和岩石学研究，结果表明，它们是在洋脊俯冲过程中侵位的.根据地球化学研究，推测日本东北部北上山脉的花岗岩与热洋板块俯冲有关。在四万十超群中的一些混杂岩单元，如那泽组（奄美大岛）、Makimine组（九州）、Okitsu混杂岩（四国西部）、Mugi组（四国东部）、Ryujin组（纪伊半岛）和Inui组（赤石山），都含有挤压和侵入到松散的细粒陆源碎屑沉积物中的绿岩.地球化学特征表明，从Shimanto超群原地绿岩类似于镁铁质熔岩产生于spresding脊。利用镜质体反射率研究了四万托和日高超群的有机变质作用。研究揭示了这两个超群的热历史.阐明了岛满岛带洋脊碰撞与沟底沉积的关系。通过对三八川变质岩的Ar/Ar同位素年龄分析，得出了三八川变质岩折返与洋脊形成的时间关系.对四万十带花岗质岩石中捕虏体的岩石学研究揭示了始新世的热事件。

The following summary of the research results obtained.1. Tere ara three rows of strata containing in in-situ greenstones at least in the Hidaka Belt. Geochemical signatures indicate that at least some of the in-situ greenstones are similar to mafic lava generated at spreading ridges.2. Geochemical and petrological studies on the igneous rocks from the Hidaka metamorphic belt have revealed that they were emplaced in connection with a ridge subduction.3. On the basis of geochemical studies, the granitic rocks in the Kitakami Mountains, Northeast Japan, are inferred to have been emplaced in connection with a subduction of a hot oceanic plate.4. Some melange-like units in the Shimanto Supergroup, such as Naze Formation(Amami-Oshima), Makimine Formation(Kyushu), Okitsu Melange(west Shikoku), Mugi Formation(east Shikoku), Ryujin Formation(Kii Peninsula) and Inui Group(Akaishi Mountains), contain greenstones which were extruded upon and intruded into unconsolidated fine-grained terrigenous clastic sediments.5. Geochemical signatures indicate that the in-situ greenstones from the Shimanto Supergroup are similar to mafic lavas generated at spresding ridges.6. Organic metamorphism in the Shimanto and Hidaka Supergroups was studied by means of vitrinite reflectance. The study has revealed thermal history of the both supergroup.7. The relationship between ridge collision and sedimentation on the trench floor in the Shimanto Belt has been clarified.8. Ar/Ar isotope ages from the Sanbagawa metamorphic rocks have resulted in the time relationship between the exhumation of the Sanbagawa metamorphic rocks and ridge cillision.9. Petrological study of xenoliths in the granitic rocks from the Shimanto Belt revealed a thermal event during the Eocene.