The Kulun region is located in the eastern Bainaimiao arc belt on the southeastern margin of the Central Asian Orogenic Belt(CAOB),adjacent to the North China Craton(NCC)to the south.This region records the closure of...The Kulun region is located in the eastern Bainaimiao arc belt on the southeastern margin of the Central Asian Orogenic Belt(CAOB),adjacent to the North China Craton(NCC)to the south.This region records the closure of the PaleoAsian Ocean during the Paleozoic to early Mesozoic and is key to study the tectonic evolution of the northern margin of the NCC.We conducted zircon U-Pb geochronology and Hf isotope analysis of volcanic-sedimentary and intrusive rocks in the Kulun region.The volcanic-sedimentary rocks were previously assigned an early Carboniferous age,but include volcanic rocks with ages of 267–266 Ma and sedimentary rocks with youngest detrital zircon age peaks of 265–244 Ma,which were intruded by a granite with an age of 242 Ma.This indicates that these rocks are actually middle Permian to Middle Triassic in age(267–242Ma)and correspond to the Qingfengshan and Liujiagou formations.Moreover,two volcanic rock samples have highεHf(t)values(+1.6 to+16.1)and relatively young two-stage Hf model ages(1095–327 Ma),indicating their sources associated with the CAOB.The age spectra and Hf isotopic characteristics of detrital zircons from the sedimentary rocks suggest that,during the middle Permian to Middle Triassic,the sedimentary provenance in the Kulun region was mainly the CAOB.However,by the Early Jurassic,the provenance changed to the NCC(i.e.,the Inner Mongolia Paleo-uplift,IMPU).This result,combined with the development of a series of conglomerates on the northern margin of the NCC in the Late Triassic(i.e.,Xingshikou,Xiaoyingzi,and Xiaohekou formations),indicates the Kulun region experienced an abrupt change in paleogeography during the Late Triassic,with the IMPU undergoing significant uplift and thus becoming the main sediment source in the Kulun region.Based on the Late Triassic alkaline igneous belt(235–215 Ma)in the IMPU,we speculate that this uplift was caused by detachment of the southward-subducting Paleo-Asian oceanic plate,which occurred in a post-orogenic extensional setting.The boundary between the NCC and CAOB(i.e.,the Bainaimiao arc belt)in the Kulun region is defined by the newly identified Paleoproterozoic granites(1.8 and 1.6 Ga)and our zircon geochronology and Hf isotope data.展开更多
In central Inner Mongolia, five gold bearing formations (Xiajining, Dongwufenzi, Wulashan, Baiyunebo and Bainaimiao Groups) belong either to volcano sedimentation or clasolite sedimentation. They formed in different t...In central Inner Mongolia, five gold bearing formations (Xiajining, Dongwufenzi, Wulashan, Baiyunebo and Bainaimiao Groups) belong either to volcano sedimentation or clasolite sedimentation. They formed in different tectonic environments such as an Archean rift zone (Xiajining and Dongwufenzi Groups), an Early Proterozoic stable basin (Wulashan Group), a Middle to Late Proterozoic continental rift zone (Baiyunebo Group), and a Paleozoic island arc environment (Bainaimiao Group). Gold contents in the gold bearing formations in the area are higher than those of other gold bearing formations in the North China Craton. However, as most gold bearing formations in the area are limited, there are a few big gold deposits in central Inner Mongolia. Gold contents in all formations were strongly influenced by migmatization and ductile shearing, the former process prompting mobilization, and the latter process resulting in gold enrichment in ductile shear zones. During the development of Archean to Proterozoic gold bearing formations, gold migrated from the mantle to the crust, then through the crust, finally deposited at the earth’s surface.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42102015&42288201)。
文摘The Kulun region is located in the eastern Bainaimiao arc belt on the southeastern margin of the Central Asian Orogenic Belt(CAOB),adjacent to the North China Craton(NCC)to the south.This region records the closure of the PaleoAsian Ocean during the Paleozoic to early Mesozoic and is key to study the tectonic evolution of the northern margin of the NCC.We conducted zircon U-Pb geochronology and Hf isotope analysis of volcanic-sedimentary and intrusive rocks in the Kulun region.The volcanic-sedimentary rocks were previously assigned an early Carboniferous age,but include volcanic rocks with ages of 267–266 Ma and sedimentary rocks with youngest detrital zircon age peaks of 265–244 Ma,which were intruded by a granite with an age of 242 Ma.This indicates that these rocks are actually middle Permian to Middle Triassic in age(267–242Ma)and correspond to the Qingfengshan and Liujiagou formations.Moreover,two volcanic rock samples have highεHf(t)values(+1.6 to+16.1)and relatively young two-stage Hf model ages(1095–327 Ma),indicating their sources associated with the CAOB.The age spectra and Hf isotopic characteristics of detrital zircons from the sedimentary rocks suggest that,during the middle Permian to Middle Triassic,the sedimentary provenance in the Kulun region was mainly the CAOB.However,by the Early Jurassic,the provenance changed to the NCC(i.e.,the Inner Mongolia Paleo-uplift,IMPU).This result,combined with the development of a series of conglomerates on the northern margin of the NCC in the Late Triassic(i.e.,Xingshikou,Xiaoyingzi,and Xiaohekou formations),indicates the Kulun region experienced an abrupt change in paleogeography during the Late Triassic,with the IMPU undergoing significant uplift and thus becoming the main sediment source in the Kulun region.Based on the Late Triassic alkaline igneous belt(235–215 Ma)in the IMPU,we speculate that this uplift was caused by detachment of the southward-subducting Paleo-Asian oceanic plate,which occurred in a post-orogenic extensional setting.The boundary between the NCC and CAOB(i.e.,the Bainaimiao arc belt)in the Kulun region is defined by the newly identified Paleoproterozoic granites(1.8 and 1.6 Ga)and our zircon geochronology and Hf isotope data.
文摘In central Inner Mongolia, five gold bearing formations (Xiajining, Dongwufenzi, Wulashan, Baiyunebo and Bainaimiao Groups) belong either to volcano sedimentation or clasolite sedimentation. They formed in different tectonic environments such as an Archean rift zone (Xiajining and Dongwufenzi Groups), an Early Proterozoic stable basin (Wulashan Group), a Middle to Late Proterozoic continental rift zone (Baiyunebo Group), and a Paleozoic island arc environment (Bainaimiao Group). Gold contents in the gold bearing formations in the area are higher than those of other gold bearing formations in the North China Craton. However, as most gold bearing formations in the area are limited, there are a few big gold deposits in central Inner Mongolia. Gold contents in all formations were strongly influenced by migmatization and ductile shearing, the former process prompting mobilization, and the latter process resulting in gold enrichment in ductile shear zones. During the development of Archean to Proterozoic gold bearing formations, gold migrated from the mantle to the crust, then through the crust, finally deposited at the earth’s surface.
