Thematic Issue: Geological and Tectonic Framework of East Asia

East Asia has been known to be an excellent field for various scopes of earth sciences, for example, there are cratons, active and old island arcs, back-arc basins, fault systems, accretionary complexes, sedimentary basins of various ages and origins, regionally metamorphic belts of various types and ages, and igneous complexes. The area is densely populated and, therefore, its understanding of the geological and tectonic framework is quite important for sustainable development of the area. An international workshop ‘International Kanazawa Workshop on Geological and Environmental Aspects of the Circum-Japan Sea Region: Toward the 21st Century’ was held at Kanazawa University, Kanazawa, Japan, on 23 September 2001, in association with the 108th Annual Meeting of the Geological Society of Japan (September 21–23). The main aims of the Workshop were to review and present new data on various aspects of geology, geoenvironment and related fields of the Circum-Japan Sea region and to propose new ideas towards further development of earth sciences, including environmental geosciences concerning East Asia, in the 21st Century. This Thematic Issue of The Island Arc is based on a selection of papers presented at the workshop. At the symposium, 14 papers were presented by delegates representing seven countries including Japan, Korea, Russia, Taiwan, Thailand, Canada and the Philippines. After the workshop, the scope of the Thematic Issue became widened by embracing the general theme of geological and tectonic framework of East Asia. In addition to six papers presented at the workshop, we have been able to include six more contributions in this special issue. The subjects discussed in this Thematic Issue are wide, from the surface to mantle processes, or from dinosaur tracks to peridotite. The articles are thematically arranged so that readers can grasp quickly the recent topics as well as advances in the filed of earth sciences related to East Asia. The collision, subduction and accretion events in the Philippines are reviewed in more detail by Yumul et al. who again provide new interpretations on the geology and tectonic settings of the key areas exemplifying the complexities involved in the geological evolution of the Philippines. A restoration model of the early Cretaceous sinistral displacement and deformation in Japan is suggested by Sasaki, based on structural mapping and the measurement of semiquantitative strain in the southern part of the South Kitakami Belt. Paik and Kim provide the pedogenic carbonate development of palustrine deposits. They demonstrate calcrete development stages in five lacustrine strata in Cretaceous Gyeongsang Basin in Korea and interpret the differences in plaustrine calcrete development in terms of paleoenvironmental parameters such as paleoclimate, lake size, and gradient. Age determination for the Cretaceous dinosaur track-bearing deposits in Korea is introduced by Kim et al., based on Rb-Sr and K-Ar methods applied to volcanic rocks and tuff intercalated in the one of the famous dinosaur track-bearing deposits in the world. Huh et al. summarize occurrences of Korean Cretaceous dinosaur fossils including footprints, eggs and nests, teeth and bones. They show that among the dinosaur fossils, the most distinctive and abundant are dinosaur tracks preserved in the lacustrine marginal deposits, and describe diverse tracks made by orninthopods, theropods and sauropods. Fusulinoidean faunal succession of a Paleo-Tethyan oceanic seamount is reported by Ueno et al. based on an intensive study at the Yutangzhai section in the central zone of the Changning-Menglian Belt of West Yunnan, South-west China. They report fusulinoidean assemblage ranging from the late Mississippian/late Early Carboniferous to late Middle Permian/late Guadalupian in thick limestones deposited on a seamount of hop spot origin. Lee and Lee make a review on Paleozoic sedimentation and tectonics in Korea based upon recent advances in understanding of sedimentary system and evolution of the Korean Paleozoic. Arakawa et al. determine the primary geochemical character of E-type mid-oceanic ridge basalt for the Proterozoic basic amphibolites of the Yeongnam massif, Korea. They discuss the variety of tectonic settings for the Proterozoic mafic igneous activities in Korea. Ishiwatari and Tsujimori present an interesting review on Paleozoic ophiolites and blueschists in Japan and Primorye, and propose a new idea of the tectonic framework of East Asia. Yumul et al. describe Cenozoic silicic volcanism in central Luzon, with a special reference to geochemical and spatial variations of the silicic magmas with time. They also discuss the importance of interaction between slab melts and mantle. Abe et al. deal with mantle peridotite xenoliths from Oki-Dogo in the Sea of Japan. They extend their discussion to the role of Japan-Sea opening on the petrological and geochemical characteristics of mantle peridotite beneath South-west Japan. Arai et al. systematically describe the mantle peridotite xenoliths in calc-alkaline basaltic andesite from Avacha volcano, the Kamchatka arc, and discuss the importance of aqueous fluid in mantle-wedge processes. We wish to express our hearty appreciation to Ishikawa Prefecture and Kanazawa City for their financial support to the International Workshop. We also thank the International Exchange Committee of Kanazawa University for the financial support to us. We are grateful to K. Tazaki, Kanazawa University and K. Hisada, University of Tsukuba, for their collaboration to successfully finish the workshop. We are greatly indebted to many colleagues for reviewing the manuscripts submitted to this thematic issue. Without their help, this issue would not have happened. We greatly appreciate the editorial assistance of Y. Tatsumi, the Japan Marine Science and Technology Center (JAMSTEC), Y. Ogawa, University of Tsukuba and S. Banno, Kyoto University, Japan. S. Arai was supported by the Center of Excellency project ‘Environmental Monitoring and Prediction of Long- and Short-Term Dynamics of Pan-Japan Sea Area: Construction of Monitoring Network and Assessment of Human Effects’ led by K. Hayakawa, Kanazawa University.

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