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40-05 03.Pdf ABSTRACTS OF PAPERS：PR］ES］ENTED AT THE SYMPOSIUM ON GEOTECTOMCS AND ENERGY RESOURCES IN EAST ASIA The Intemational Symposium entitled“Geotectonics and Energy Resources in East Asia”was held in September1988，as a part of the Institute for Transfer of Industrial Technology Programme of the Agency of Industrial Science and Technology． Thirteen experts in the field of geotectonics and resource assessment presented papers at the symposium．The abstracts of the papers are appeared in the following Pages． The result of the symposium will bear fruit in the near future as geotectonic maps and basin maps of East Asia in the course of the inter－ national activities conducted by CPMP（Circum－Paci丘c Map Project）and CCOP （Committee for Co－ordination of Joint Prospecting for Mineral Resources in Asian Offshore Areas）． Number of tectonic models have been GEOTECTON亙CS OF EAST AS亘A presented alrea（iy， in trying to interpret this Tadashi SATO complex history．Paleomagnetic study now in Uη加θrs酸y o∫Ts醜めα，」αPαη wide use，for instance，led us to the decomposi－ tion of apParently cohesive continent．It must The present structure of East Asia is a be，of course，consistent with the data丘om time section of the long history of the region the traditional but basic information of frora the Precambrian to Recent．It stems stratigraphy， geological structures an（l fossil from the interactions among （ii任erent plates． records． It is eagerly wanted to organize all We have a wide variety of structures resulted the available（iata for better un（ierstanding of from almost all the kinds of plate boundary the structure of this part of the earth． tectonism in this part of the earth。 The geotectonic maps of East Asia aim at Surroun（1ing the continental core， ocean－ summarizing such basic data in a form of map， COntinent interaCtiOn COnStrUCte（1 eXtenSiVely which will be used not only for direct economic island arc systems．We can see，besides these， development but also for further tectonic local arc－arc an（1 continent－arc collision me（iitation． boundaries，translational margins and others in the present East Asia． ACCRET亘ONARy TECTON亙CS亘N JAPAN Inside the continent，the geologic constitu－ tion is far from simple or clear－cut．The Koji WAKITA continent of Asia is a heterogeneous assem－ GθoZo8‘cαZS脆rひθッoゾ」αPαπ’ blage of paleoplates and fold belts， accreted successively by addition of new elements． Before the Japan Sea was open in the The primary structures of the constitutent Miocene，the Japanese islands had been elements are often secondarily modified by situated at the eastem margin of the Asian later deformation．Bent arcs，twisted moun－ continent．Along this continental margin， tains，fracturedlandsarenotrare．Younger oceanic plates have been sub（1ucte（l since， at movements resulted in superposition of defor－ least，1ate Paleozoic time．Most of the matiOnal featUreS， making 伍e StrUCtUra玉 geologic entities in the Japanese islands were analyses（li伍cult． cause（1 by the accretion of trench－flll sedi一 一251一 B沼ε伽oμんeσθoZo8‘oαZS乱ruθyo∫」αPαπ．VoZ．40，ノ〉o。5 ments，pelagic sediments，and fragments of an（l Tokoro terra．nes， SeamOUntS，iSland arCS and miCrOCOntinentS （6）Paleogene accretionary complex： the along the active continental margin during Southem Shimanto terrane， about300mi皿on years（Fig．1）．The follow－ （7）Neogrene－Recent accretionary complex：t虹e ing accretionary complexes are discriminated in Nankai trough． Japan： Among them，the Hida terrane is consid－ （1）continentalfragments：theHidaterrane ered to have constitute（i a part of the Sino－ and the Southern Kitakami－Abukuma Korean Massif before the opening of the Japan terrane， Sea．The terrane consists mainly of poly一 （2） tectonically squeezed fragments of island metamorphosed gneiss and Jurassic granite． arcs and Paleozoic accretionary com－ Rb－Sr radiometric ages of the gneiss and plexes：the Circum－Hida Tectonic Zone associate（l intrusive rocks are 1100， 700，300， and the Kurosegawa Tectonic Zone， 240 an（1 180 Ma． These rocks are covered by （3） Late Paleozoic accretionary complex：the Middle Jurassic to Early Cretaceous shallow Ckugok：u composite terrane comprising the marine to non－marine molasse－type sedimen－ Sangun，Maizuru，Akiyoshi and Ultra－ taryrocks． Tamba terranes，and a part of the Chichibu The Circum－Hida Tectonic Zone extends terrane， along the southeastem margin of the Hida （4） Jurassic accretionary complex：the Mino－ terrane．The zone is a heterogeneous assem－ Tamba terrane，Northern Kitakami terrane blage of fragments of various rocks such as an（l a part of Chichibu terrane， non－metamorphosed Ordovician to Permian （5） Cretaceous accretionary complex： the shallow marine sedimentary rocks，chloritoid Northem Shimanto，Sorachi－Ezo，Hidaka， phyllite an（l schistose rocks （greenschist一 EヨC・ntinentaIfragments Early Paleozolc accretionary comp『ex Sorachi－Ezo i．ノ （Locaily metamorphosed，High P／Low T） terrane 團 Hidaka Late Paleozoic accretionary，cQmpiex terrane （non－metamorphosed） ／ 圏 ．．！ 講 （metamorphosed，High P／LowT） Jurassic accretionary complex 皿 （non－metamorphosed） 罰 （metamorphQsed，High T／Low P） 羅 （metamorphosed，High P／Low T） 匿翻Cretace・usaccreti・naryc・mplex 観le 目Pale・geneaccretbnaryc・mpiex ’ Northern Kitakami Terrane boundary terrane Circum－Hida 、、 Chugoku terrane Tectonic zone ㊦ Wakasa ？ 榊榊や 翻龍i一一一一翻9一一颪、￥ Maizuru i“ も ドむロ 號鴇 ＿ 、、 te「「ane 争： ？ 汚 ◎Hida terrane 蝶 Southem Kitakami ？ －Abukuma terrane I l一 幽蓼．一 ，Sa翻繭a Ult「a一儲e 郵 証 ！ 團 Ryoke metamorphic ？ rocks ♀魏鼎 Kurosegawa － Northem Shimanto Tectonic c皇階鵠 zone（ΦlNorthern Shimanto terrane terrane Southern Shimanto terrane Fig．1 Pre－Neogene tectonic units of Japan， 一252一 ．肋s惚c孟so∫PαPεrsα材んθ1四丁融即os‘ωm glaucophane schist facies）of300－400Ma． to Late Cretaceous trench－fill sediments They are tectonically squeezed out an（l associated with pelagicもediments and accreted embedded in serpentinite．The assemblage is remnants of Late Jurassic to E＆rly Cretaceous overlain by Lower Jurassic to Early Cretaceous seamounts．The Sorachi－Ezo terrane is shallow marine to non－marine molasse－type characterized by forearc sediments，ophiolite SedimentaryrOCkS． and melanges．The Tokoro terrane consists of The Kurosegawa Tectonic Zone includes accrete（1 trench一且ll se（iiments， pelagic se（1i－ heterogeneous rocks which are tectonically ments and seamounts．A part of the squeezed out and embedded in serpentinite as complexe串in the Hidaka terrane is affected by well as the Circum－Hida Tectonic Zone．Early the high T／low P type metamorphism，while a Paleozoicgranite，volcanicrocks，gneissand part of the Sorachi－Ezo terrane is affected by schist， and Paleozoic to Mesozoic shallow the high P／10w T type metamorphism． marine sedimentary rocks occur in the The Paleogene accretionary complex Kurosega、wa Tectonic Zone． composed mainly of accreted trench－fill The Paleozoic accretionary complexes are sediments constitutes the Southem Shimanto distributed in the Chugoku composite terrane terrane． It is distribute（l along the Pεしcific （Sangun，Maizuru and Akiyoshi terranes）。A coast in the Southwest Japan，a、nd is in contact considerεlble part of the Paleozoic accretionary with the Neogene to Recent accretionary complexes is affected by the high P／10w T type complex in the Nankai Trough． metamorphism （Sangun metamorphic rocks）． Eεしch of the Pre－Neogene εしccretionary The non－metamorphosed part of the complexes events has been followed by complex strike slip is composed of chaotic mixtures of Middle to and thrust faulting．Such multiple tectonic Late Permian trench一且ll sediments，Middle deformation an（i（1islocation have（listurbed the Permian pelagic sediments and accreted original arrangement of the individual accre－ remnants of Carboniferous to Permian tiOnary COmpleXeS． seamounts．Radiometric dating shows that Non－marine to shallow marine intra－arc the metamorphosed part includes older se（1iments have covere（i the previously accrete（i elements than the non－metamorphosed part of complexes since Mesozoic time．Igneous Permian age． activities during the formation of the Jurassic The Jurassic accretionary complexes of the accretionary complexes and the Cretaceous and Mino－Tamba and Chichibu terranes consist P＆leogene accretionary complexes were record－ mainly of Early Jurassic to Early Cretaceous ed in the Jurassic granite of the Hi（1a terrane trench－Hll se（iiments， Permian to Jurassic an（i in the acid plutono－volcanic rocks of the pelagic sediments and accreted remnants of Northeast Japan an（1 the Inner zone of the Late Paleozoic seamounts．These components Southwest Japan，respectively． were fragmentated and mixed each other，and The accretionary process is in progress in often constitute melanges which，are composed the Nankai Trough of the Southwest Japan of numerous blocks of various rock types and still now，while tectonic erosion occurs in the ages embedded in muddy matrix。The Japan Trench of the Northeast Japan． The complexes are locally affected by the high present collision of the Izu－Mariana arc to T／low P type（Ryoke metamorphic rocks）and Japan is a symbolic manifestation of the the high P／low T type metamorphism（Samba－ accretionary tectonics in the Japanese Islands． gawa metamorphic rocks＆nd a part of the Sangun metamorphic rocks．）． The Cretaceous， mostly non－metamor－ phosed，accretionary complexes occupy the Northem Shimanto，Sorachi－Ezo，Hidaka and Tokoro terranes。 The Northern Shimanto an（i Hidaka terranes are composed mostly of Early 一253一 BωZ乙ε莇η oノオんε GθoZo9ε（）αZ S脆rひεツ oノ」α∫）αη。V’oL 40，ハτo。5 non－marine an（l marine strata in the Pohang area overlie the Cretaceous Gyeongsang strata TECTONICS OF SOUTHERN KOREA an（1the associate（1volcanic an（i plutonic
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