The origin of the central Qiangtang metamorphic belt(CQMB)has long been in debate,which is not clear whether this belt is the exhumed Jinsha oceanic plate that had been subducted and underthrusted beneath the Qiangtan...The origin of the central Qiangtang metamorphic belt(CQMB)has long been in debate,which is not clear whether this belt is the exhumed Jinsha oceanic plate that had been subducted and underthrusted beneath the Qiangtang Block,or the in situ Longmu Co-Shuanghu suture that separated the south and north Qiangtang blocks.Here we report field observations,zircon U-Pb ages and Lu-Hf isotopes,as well as whole rock geochemistry and Sr-Nd isotopes of the Late Triassic volcanic rocks near the Chabo Co within the southern margin of the CQMB.The ca.229 Ma Chabo Co volcanic rocks and limestones possess characteristic lithologies of a seamount.Their geochemical and isotopic compositions are similar to OIB-type lavas.Unlike other metabasalts(eclogites and blueschists)in the CQMB,the Chabo Co volcanic rocks are OIB-type lavas that did not experience high-grade metamorphism;this is likely because that the Chabo Co seamount was detached from the subducting Longmu Co-Shuanghu oceanic slab.This work provides new solid evidences for an in situ origin of the CQMB.展开更多
The Qiangtang basin is located between Kekexili-Jingshajiang suture belt and Bangong-Lujiang suture belt, and is divided into the north part and south part by the central uplift that has no crop out of Mesozoic strata...The Qiangtang basin is located between Kekexili-Jingshajiang suture belt and Bangong-Lujiang suture belt, and is divided into the north part and south part by the central uplift that has no crop out of Mesozoic strata. When the Jinshajiang Ocean was closed, the subducting plate was subducted southward. In the central part of the Qiangtang basin, the cushioning effect of the asthenosphere resulted in the thermal doming of the mantle and subsequent large-scale anatexis. Mantle source materials and antectic materials were upwelled and extruded into the middle crust, leading to the thickening of the middle crust and the heating and weakening of the middle to upper crust, and resulting in the rapid deformation (detachment) and tectonic erosion, and in the isostatic uplifting and the formation of metamorphic core complex. The upwelling of anatectic materials would further enhance the buoyant repercussion, which would combine with the side stress due from extrusion in resulting in the formation of an extensional stress field. The extensional structure and detachment fault are formed under the influence of the losing stabilized gravitation. In the deformation area in both the upper part and the lower part, an extensional deposition area would be formed, and this is the generation of a new basin.The metamorphic core complex of the central uplift is comprised of gneiss, which is itself overlain by non-metamorphic to weakly metamorphic covering strata intersected by faults.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 41702212,41672054)the Fundamental Research Funds for Central Universities,China University of Geosciences (Wuhan) (Nos. CUGL170816 and CUGQYZX1745)
文摘The origin of the central Qiangtang metamorphic belt(CQMB)has long been in debate,which is not clear whether this belt is the exhumed Jinsha oceanic plate that had been subducted and underthrusted beneath the Qiangtang Block,or the in situ Longmu Co-Shuanghu suture that separated the south and north Qiangtang blocks.Here we report field observations,zircon U-Pb ages and Lu-Hf isotopes,as well as whole rock geochemistry and Sr-Nd isotopes of the Late Triassic volcanic rocks near the Chabo Co within the southern margin of the CQMB.The ca.229 Ma Chabo Co volcanic rocks and limestones possess characteristic lithologies of a seamount.Their geochemical and isotopic compositions are similar to OIB-type lavas.Unlike other metabasalts(eclogites and blueschists)in the CQMB,the Chabo Co volcanic rocks are OIB-type lavas that did not experience high-grade metamorphism;this is likely because that the Chabo Co seamount was detached from the subducting Longmu Co-Shuanghu oceanic slab.This work provides new solid evidences for an in situ origin of the CQMB.
文摘The Qiangtang basin is located between Kekexili-Jingshajiang suture belt and Bangong-Lujiang suture belt, and is divided into the north part and south part by the central uplift that has no crop out of Mesozoic strata. When the Jinshajiang Ocean was closed, the subducting plate was subducted southward. In the central part of the Qiangtang basin, the cushioning effect of the asthenosphere resulted in the thermal doming of the mantle and subsequent large-scale anatexis. Mantle source materials and antectic materials were upwelled and extruded into the middle crust, leading to the thickening of the middle crust and the heating and weakening of the middle to upper crust, and resulting in the rapid deformation (detachment) and tectonic erosion, and in the isostatic uplifting and the formation of metamorphic core complex. The upwelling of anatectic materials would further enhance the buoyant repercussion, which would combine with the side stress due from extrusion in resulting in the formation of an extensional stress field. The extensional structure and detachment fault are formed under the influence of the losing stabilized gravitation. In the deformation area in both the upper part and the lower part, an extensional deposition area would be formed, and this is the generation of a new basin.The metamorphic core complex of the central uplift is comprised of gneiss, which is itself overlain by non-metamorphic to weakly metamorphic covering strata intersected by faults.
