U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using...U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using a laser ablation inductively coupled plasma mass spectrometer（LA-ICP-MS）. The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. We obtained 515 concordant to slightly discordant zircon ages ranging from ca. 3566 to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic（249e79 Ma） and Paleoproterozoic（2491e1691 Ma） ages with subordinate Archean ages indicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage basins of the South Korean rivers and the crustal growth of the southern Korean Peninsula was focused in these two periods. Comparison of detrital zircon-age data between the North and South Korean river sediments reveals that the Paleoproterozoic zircon age distributions of both regions are nearly identical,while the Neoproterozoice Paleozoic ages exist and the Mesozoic ages are dominant in southern Korean Peninsula. This result suggests that Precambrian terrains in Korea record the similar pre-Mesozoic magmatic history and that the influence of Mesozoic magmatism was mainly focused in South Korea.展开更多
The Lower Cretaceous Sindong Group in southeastern Korea is a fluvio-lacustrine sedimentary package deposited in an elongated basin formed by extension in an active continental margin setting.To characterize its chang...The Lower Cretaceous Sindong Group in southeastern Korea is a fluvio-lacustrine sedimentary package deposited in an elongated basin formed by extension in an active continental margin setting.To characterize its changes in paleodrainage system,we analyzed U-Pb ages of detrital zircons in sandstones from each stratigraphic units in northern,central,and southern parts of the Sindong Group.Detrital zircons show a wide range of ages from 106 Ma to 3494 Ma with spatiotemporal variations in age population.Detrital zircon age spectra and paleocurrent data reveal that at least three drainage basins sourced to the Early Cretaceous river system in the Yeongnam Massif.The drainage system for the central portion of the basin was consistent with time,whereas those for the northern and southern portions shifted between the Nakdong Formation and Hasandong Formation.The strong influences resulting from the confluence of dispersal path draining Jurassic granitoids,possibly aided by faulting activity,likely caused the replacement of paleodrainage system in the northern portion.The drainage system of the southern portion was changed by extension of the drainage basin to the source terrane having similar geology to or shared the source terrane for the paleoflow system for the central portion.展开更多
The late Miocene–early Pliocene Taitao ophiolite is exposed~30 km southeast of the Chile triple junction,where a spreading center of the Chile ridge system is subducting underneath the South America plate.This unique...The late Miocene–early Pliocene Taitao ophiolite is exposed~30 km southeast of the Chile triple junction,where a spreading center of the Chile ridge system is subducting underneath the South America plate.This unique tectonic setting provides an excellent opportunity to study the emplacement mechanism of a ridge-trench intersection ophiolite and the complex magmatic interactions between the subducting ridge,overlying crust and sediments,and the mantle wedge.As a result of these interactions,several granitic plutons were formed contemporaneously with emplacement of the ophiolite.We review previous studies of the Taitao ophiolite and use new geochemical data to discuss the mechanism that formed juvenile magma of calc-alkaline I-type granites during ridge subduction.Our model implies that the magmas of the Taitao granites formed due to partial melting of hot oceanic crust adjacent to the subducting mid-oceanic ridge that has been contami-nated by deep crustal material and/or metasomatized sub-arc mantle.The partial melting took place under garnet-free amphibolite conditions.The juvenile magmas then incorporated different amounts of subducted sediments and/or continental material to form the I-type granites with various compositions.Subduction of fracture zones played an important role in these processes.展开更多
基金supported by a grant from the Korea Research Foundation (NRF-2014R1A1A2059895)partly supported by the cooperative research program of the Earthquake Research Institute, The University of Tokyo, Japan
文摘U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using a laser ablation inductively coupled plasma mass spectrometer（LA-ICP-MS）. The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. We obtained 515 concordant to slightly discordant zircon ages ranging from ca. 3566 to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic（249e79 Ma） and Paleoproterozoic（2491e1691 Ma） ages with subordinate Archean ages indicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage basins of the South Korean rivers and the crustal growth of the southern Korean Peninsula was focused in these two periods. Comparison of detrital zircon-age data between the North and South Korean river sediments reveals that the Paleoproterozoic zircon age distributions of both regions are nearly identical,while the Neoproterozoice Paleozoic ages exist and the Mesozoic ages are dominant in southern Korean Peninsula. This result suggests that Precambrian terrains in Korea record the similar pre-Mesozoic magmatic history and that the influence of Mesozoic magmatism was mainly focused in South Korea.
基金funded by the National Research Foundation of Korea(NRF-2014R1A2A2A01005404,2017R1A2B4007877,2017R1C1B1007653).
文摘The Lower Cretaceous Sindong Group in southeastern Korea is a fluvio-lacustrine sedimentary package deposited in an elongated basin formed by extension in an active continental margin setting.To characterize its changes in paleodrainage system,we analyzed U-Pb ages of detrital zircons in sandstones from each stratigraphic units in northern,central,and southern parts of the Sindong Group.Detrital zircons show a wide range of ages from 106 Ma to 3494 Ma with spatiotemporal variations in age population.Detrital zircon age spectra and paleocurrent data reveal that at least three drainage basins sourced to the Early Cretaceous river system in the Yeongnam Massif.The drainage system for the central portion of the basin was consistent with time,whereas those for the northern and southern portions shifted between the Nakdong Formation and Hasandong Formation.The strong influences resulting from the confluence of dispersal path draining Jurassic granitoids,possibly aided by faulting activity,likely caused the replacement of paleodrainage system in the northern portion.The drainage system of the southern portion was changed by extension of the drainage basin to the source terrane having similar geology to or shared the source terrane for the paleoflow system for the central portion.
基金supported by grant-in-aid for Science Research 13373004 and 15H02630 by the Ministry of Education,Culture,Sports,Science and Technology of Japan.
文摘The late Miocene–early Pliocene Taitao ophiolite is exposed~30 km southeast of the Chile triple junction,where a spreading center of the Chile ridge system is subducting underneath the South America plate.This unique tectonic setting provides an excellent opportunity to study the emplacement mechanism of a ridge-trench intersection ophiolite and the complex magmatic interactions between the subducting ridge,overlying crust and sediments,and the mantle wedge.As a result of these interactions,several granitic plutons were formed contemporaneously with emplacement of the ophiolite.We review previous studies of the Taitao ophiolite and use new geochemical data to discuss the mechanism that formed juvenile magma of calc-alkaline I-type granites during ridge subduction.Our model implies that the magmas of the Taitao granites formed due to partial melting of hot oceanic crust adjacent to the subducting mid-oceanic ridge that has been contami-nated by deep crustal material and/or metasomatized sub-arc mantle.The partial melting took place under garnet-free amphibolite conditions.The juvenile magmas then incorporated different amounts of subducted sediments and/or continental material to form the I-type granites with various compositions.Subduction of fracture zones played an important role in these processes.
