Estimation of accretionary complex growth by micropaleontological mapping

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The oceanic plate stratigraphy (OPS) of different tectonostratigraphic units is compared with 3-5 times accuracy by using a framewok of Jurassic-Lower Cretaceous radiolarian zonation and its numerical age callibration of Matsuoka (1995). A tectonostratigraphic unit division for the Chichibu composite terrane is poroposed on the basis mainly of lithofacies. The OPSs of the Kamiyoshida Unit and Kashiwagi Unit in the Northern Chichibu terrane are similar to those of the Togano and Sambosan Unit in the Southern Chichibu Terrane, respectively. Some critical differences in OPS of the above-mentioned pair of the tectonositratigraphic units are also recognized. This indicates that the Nothern Chichibu and Southern Chichibu terranes were formed by the subduction of the same oceanic plate along a single subduction zone at laterally distant places and they were juxtaposed in later tectonic events characterized by strike-slip movements. Comparison of OPSs among Jurassic accretionary complexes in Southwest Japan suggests that the main strike-slip dislocation took place along the Kurosegawa Tectonic Zone rather than the Median Tectonic Line.The Pacific-Japan radiolarian zonal scheme is also applicable to accretionary complexes of the Yarlung Zangbo Suture Zone in southern Tibet, of the North Palawan Block in the Philippines, and of Sikhote Alin in Russian Far East. Detailed radiolarian biostratigraphic research on Upper Jurassic interval at ODP Site 801 in the western Pacific reveals that two zonal schemes proposed independently from Pacific-Japan and North America are well correlated with each other.