The last appearance datum of the radiolarian Kilinora spiralis is recorded above the first appearance datum of the ammonite Ataxioceras (A.) kurisakense in the Todoro Section of the Kurisaka Formation, Southern Kurose...The last appearance datum of the radiolarian Kilinora spiralis is recorded above the first appearance datum of the ammonite Ataxioceras (A.) kurisakense in the Todoro Section of the Kurisaka Formation, Southern Kurosegawa Terrane, Shikoku, SW Japan. The constraint by ammonite age prolongs the range of the Kilinora spiralis Zone, a remarkable Jurassic radiolarian zone in Japan-NW Pacific region, into the lower Kimmeridgian. The direct correlation of the Kilinora spiralis zone with the Late Jurassic ammonite faunal succession in the Kurisaka Formation will provide a clue to the still pending chronological difference between European and North American radiolarian zones.展开更多
The Kurosegawa belt forms a relatively narrow terrane that can be traced continuously throughout southwest and central Japan.The major constituent continental fragments of the Kurosegawa belt include Early Paleozoic g...The Kurosegawa belt forms a relatively narrow terrane that can be traced continuously throughout southwest and central Japan.The major constituent continental fragments of the Kurosegawa belt include Early Paleozoic granitic rocks,high-grade展开更多
The point at issue:The Kurosegawa Terrane is composed of continental fragments transecting Mesozoic terranes of accretionary complex in Southwest Japan(Fig.1).It is an attenuated tectonic sliver and considered to be a...The point at issue:The Kurosegawa Terrane is composed of continental fragments transecting Mesozoic terranes of accretionary complex in Southwest Japan(Fig.1).It is an attenuated tectonic sliver and considered to be allochthonous with respect to the main part of Southwest Japan.The problem of which continental block in the East Asian continental margin is the source of the Kurosegawa Terrane has puzzled Japanese geologists for many years.Firstly,we try to approach this issue based on the analysis of fusulinacean assemblage in accreted terranes composed of subduction complex in the Pacific Rim.Secondly,by applying the result of this analysis we try to locate the source of the continental fragments of the Kurosegawa Terrane.Thirdly,we try to prove its validity with a new paleomagnetic study.展开更多
Ordovician diorite-quartz diorite mylonite(Saganoseki quartz diorite) was discovered in Sambagawa metamorphic terrane at the northern margin of Saganoseki Peninsula,Kyushu Island,Japan.The LA-ICP-MS zircon U-Pb geochr...Ordovician diorite-quartz diorite mylonite(Saganoseki quartz diorite) was discovered in Sambagawa metamorphic terrane at the northern margin of Saganoseki Peninsula,Kyushu Island,Japan.The LA-ICP-MS zircon U-Pb geochronology revealed that the intrusion age of Saganoseki quartz diorite was 473.3±3.6 Ma.These rocks show the volcanic arc affinity based on the trace element composition.On the basis of geochronological and geochemical results,Saganoseki quartz diorite is considered to be a member of the Early Paleozoic igneous rocks of the Kurosegawa tectonic zone.Saganoseki quartz diorite is located just south of the Median Tectonic Line(MTL)and is in close contact with the pelitic and psammitic schist without any brittle shear zone.U-Pb ages of detrital zircon grains from two psammitic schists show the estimated sedimentation age of early Late Cretaceous,indicate that these psammitic schists are the member of Sambagawa metamorphic rocks.Together with these results and the mode of occurrence in the field,we argue that the Early Paleozoic igneous rocks of the Kurosegawa tectonic zone existed as an upper structural unit of the Sambagawa terrane.This relationship is the key to reconstruct the Mesozoic tectonics of Japan as a part of East Asia,and its evolution through time.展开更多
文摘The last appearance datum of the radiolarian Kilinora spiralis is recorded above the first appearance datum of the ammonite Ataxioceras (A.) kurisakense in the Todoro Section of the Kurisaka Formation, Southern Kurosegawa Terrane, Shikoku, SW Japan. The constraint by ammonite age prolongs the range of the Kilinora spiralis Zone, a remarkable Jurassic radiolarian zone in Japan-NW Pacific region, into the lower Kimmeridgian. The direct correlation of the Kilinora spiralis zone with the Late Jurassic ammonite faunal succession in the Kurisaka Formation will provide a clue to the still pending chronological difference between European and North American radiolarian zones.
文摘The Kurosegawa belt forms a relatively narrow terrane that can be traced continuously throughout southwest and central Japan.The major constituent continental fragments of the Kurosegawa belt include Early Paleozoic granitic rocks,high-grade
文摘The point at issue:The Kurosegawa Terrane is composed of continental fragments transecting Mesozoic terranes of accretionary complex in Southwest Japan(Fig.1).It is an attenuated tectonic sliver and considered to be allochthonous with respect to the main part of Southwest Japan.The problem of which continental block in the East Asian continental margin is the source of the Kurosegawa Terrane has puzzled Japanese geologists for many years.Firstly,we try to approach this issue based on the analysis of fusulinacean assemblage in accreted terranes composed of subduction complex in the Pacific Rim.Secondly,by applying the result of this analysis we try to locate the source of the continental fragments of the Kurosegawa Terrane.Thirdly,we try to prove its validity with a new paleomagnetic study.
基金This study was supported by the Fukada Geological Institute[Fukada Grant-in-Aid].
文摘Ordovician diorite-quartz diorite mylonite(Saganoseki quartz diorite) was discovered in Sambagawa metamorphic terrane at the northern margin of Saganoseki Peninsula,Kyushu Island,Japan.The LA-ICP-MS zircon U-Pb geochronology revealed that the intrusion age of Saganoseki quartz diorite was 473.3±3.6 Ma.These rocks show the volcanic arc affinity based on the trace element composition.On the basis of geochronological and geochemical results,Saganoseki quartz diorite is considered to be a member of the Early Paleozoic igneous rocks of the Kurosegawa tectonic zone.Saganoseki quartz diorite is located just south of the Median Tectonic Line(MTL)and is in close contact with the pelitic and psammitic schist without any brittle shear zone.U-Pb ages of detrital zircon grains from two psammitic schists show the estimated sedimentation age of early Late Cretaceous,indicate that these psammitic schists are the member of Sambagawa metamorphic rocks.Together with these results and the mode of occurrence in the field,we argue that the Early Paleozoic igneous rocks of the Kurosegawa tectonic zone existed as an upper structural unit of the Sambagawa terrane.This relationship is the key to reconstruct the Mesozoic tectonics of Japan as a part of East Asia,and its evolution through time.
