在Columbia超大陆的聚合和裂解过程中,扬子板块西南缘扮演着重要角色,前人认为Columbia超大陆在古元古代末期—中元古代中期裂解,对于其最初裂解在扬子板块西南缘的响应时间存在~1.85 Ga及~1.75 Ga两种认识(Liu Kang et al.,2019;刘军平...在Columbia超大陆的聚合和裂解过程中,扬子板块西南缘扮演着重要角色,前人认为Columbia超大陆在古元古代末期—中元古代中期裂解,对于其最初裂解在扬子板块西南缘的响应时间存在~1.85 Ga及~1.75 Ga两种认识(Liu Kang et al.,2019;刘军平等,2020)。扬子板块西南缘广泛分布的古元古代1.77~1.65 Ga板内镁铁质岩浆活动代表着超大陆裂解的高峰,而古元古代双峰式岩浆作用则相对罕见。展开更多
Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boun...Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary.However,the intimate relationship between their origins and the dynamic mechanisms are unclear,as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition(OST).In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks(i.e.,the intracontinental Kwangsian Orogeny),two stratigraphic sections respectively in Zhaotong area(Northeast Yunnan)and Puyi area(Northwestern Guizhou)that were located in the semi-restricted inner Yangtze Sea during the OST were systematically studied,on the basis of whole-rock geochemical composition,pyriteδ^(34)S(δ^(34)Spy),total organic carbon(TOC),stable Sr isotope,pyrite framboid size distribution and zircon U-Pb age,trace elements.The evidence shows that the paleo-oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation.These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval.Based on previous research on the genetic relationship between black shale series and plate tectonic movement,a basin-mountain evolution model suitable for South China in the Late Ordovician is presented.The two bentonites in the Wufeng Formation with U-Pb ages of 445.5±0.8 Ma and 441.9±2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician,the provenance region probably being located in the Jiangnan orogenic belt.Thus,we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin-mountain transformation and the Kwangsian Orogeny in South China,which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.展开更多
文摘在Columbia超大陆的聚合和裂解过程中,扬子板块西南缘扮演着重要角色,前人认为Columbia超大陆在古元古代末期—中元古代中期裂解,对于其最初裂解在扬子板块西南缘的响应时间存在~1.85 Ga及~1.75 Ga两种认识(Liu Kang et al.,2019;刘军平等,2020)。扬子板块西南缘广泛分布的古元古代1.77~1.65 Ga板内镁铁质岩浆活动代表着超大陆裂解的高峰,而古元古代双峰式岩浆作用则相对罕见。
基金funded by the China Geological Survey Basic Public Welfare Comprehensive Geological Survey Project(DD20191012,ZD20220504)the Chinese National Natural Science Foundation(42102065)。
文摘Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary.However,the intimate relationship between their origins and the dynamic mechanisms are unclear,as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition(OST).In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks(i.e.,the intracontinental Kwangsian Orogeny),two stratigraphic sections respectively in Zhaotong area(Northeast Yunnan)and Puyi area(Northwestern Guizhou)that were located in the semi-restricted inner Yangtze Sea during the OST were systematically studied,on the basis of whole-rock geochemical composition,pyriteδ^(34)S(δ^(34)Spy),total organic carbon(TOC),stable Sr isotope,pyrite framboid size distribution and zircon U-Pb age,trace elements.The evidence shows that the paleo-oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation.These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval.Based on previous research on the genetic relationship between black shale series and plate tectonic movement,a basin-mountain evolution model suitable for South China in the Late Ordovician is presented.The two bentonites in the Wufeng Formation with U-Pb ages of 445.5±0.8 Ma and 441.9±2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician,the provenance region probably being located in the Jiangnan orogenic belt.Thus,we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin-mountain transformation and the Kwangsian Orogeny in South China,which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.
