Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids.Precise LAICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples,yielding crystalliz...Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids.Precise LAICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples,yielding crystallization ages of 822.6±5.8 Ma and 822.2±6.2 Ma,respectively.The consistent ages within analytical errors with the host granitoids suggested that they were the products of the same magmatism.The microcrystalline-dioritic enclaves commonly show plastic forms and contain similar plagioclase megacrysts to the host rocks,and both of the enclaves and host granitoids showed a complex composition and structural imbalance in plagioclases.Furthermore,the apatites with a euhedral acicular shape occurred widely in the microcrystalline-dioritic enclaves.All of these petrographic features above imply magma mixing is involved in their diagenesis.The enclaves and host granitoids show a marked zircon trace element difference and Hf isotopic signatures without correlation in zircon trace element pairs but form their own system between enclaves and host granitoids.Additionally,most of the zircons show extremely high εHf (t) with εHf (t) =3.54?11.94 from the southern samples,and εHf (t) =1.0?9.09 from the central region.Some zircons with the higher εHf (t) are similar to the zircons from the juvenile island arc in the eastern segment of Jiangnan Orogen.Integrated geological and Hf isotopic characteristics suggest microcrystalline-dioritic enclaves were derived from the partial melting process of the Mesoproterozoic crust which enriched juvenile island arc materials and mixed with the granitic magma that remelted from the Mesoproterozoic continental crust which relatively enriched ancient sediments and mixed with the host granitoid in diagenesis.展开更多
There are widespread Mesozoic–Cenozoic terrestrial volcanic activities in East China,and they produced favorable geologic factors for the volcanic reservoirs.To reveal the spatio-temporal evolution of regional volcan...There are widespread Mesozoic–Cenozoic terrestrial volcanic activities in East China,and they produced favorable geologic factors for the volcanic reservoirs.To reveal the spatio-temporal evolution of regional volcanisms and their tectonic setting,we subdivide Mesozoic–Cenozoic volcanic activities into 6 volcanic cycles(Ⅰ–Ⅵ),and summarize the temporal-spatial distribution,rock association and tectonic setting of each cycle.The Cycle I forms a post-orogenic intraplate bimodal volcanic association.The cyclesⅡandⅢinclude arc volcanic associations formed in compressional and extensional subduction environments,respectively.The CycleⅣcontains a post-orogenic arc bimodal association.The CycleⅤis a basaltic association of tholeiite series under initial rift setting,and the CycleⅥis basaltic association of alkaline series under typical rift setting.The volcanic strata between each cycle are bounded by regional unconformity.The above 6 volcanic cycles correspond to 6 sequential stages of tectonic evolutions from the Early Jurassic post-orogeny,the Mid-Jurassic–Cretaceous subduction of the paleo-Pacific Plate to the Cenozoic marginal rifting.According to the geological characteristics of volcanic reservoirs in different volcanic cycles,it is put forward that the CycleⅤis the major formation period of volcanic reservoirs in East China and should be the focus of exploration,and that the volcanic reservoirs of the CycleⅣare also worthy of attention.展开更多
文摘Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids.Precise LAICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples,yielding crystallization ages of 822.6±5.8 Ma and 822.2±6.2 Ma,respectively.The consistent ages within analytical errors with the host granitoids suggested that they were the products of the same magmatism.The microcrystalline-dioritic enclaves commonly show plastic forms and contain similar plagioclase megacrysts to the host rocks,and both of the enclaves and host granitoids showed a complex composition and structural imbalance in plagioclases.Furthermore,the apatites with a euhedral acicular shape occurred widely in the microcrystalline-dioritic enclaves.All of these petrographic features above imply magma mixing is involved in their diagenesis.The enclaves and host granitoids show a marked zircon trace element difference and Hf isotopic signatures without correlation in zircon trace element pairs but form their own system between enclaves and host granitoids.Additionally,most of the zircons show extremely high εHf (t) with εHf (t) =3.54?11.94 from the southern samples,and εHf (t) =1.0?9.09 from the central region.Some zircons with the higher εHf (t) are similar to the zircons from the juvenile island arc in the eastern segment of Jiangnan Orogen.Integrated geological and Hf isotopic characteristics suggest microcrystalline-dioritic enclaves were derived from the partial melting process of the Mesoproterozoic crust which enriched juvenile island arc materials and mixed with the granitic magma that remelted from the Mesoproterozoic continental crust which relatively enriched ancient sediments and mixed with the host granitoid in diagenesis.
基金supported by the State Key R&D Project of the Ministry of Science and Technology of China(No.2016YFC06002010).
文摘There are widespread Mesozoic–Cenozoic terrestrial volcanic activities in East China,and they produced favorable geologic factors for the volcanic reservoirs.To reveal the spatio-temporal evolution of regional volcanisms and their tectonic setting,we subdivide Mesozoic–Cenozoic volcanic activities into 6 volcanic cycles(Ⅰ–Ⅵ),and summarize the temporal-spatial distribution,rock association and tectonic setting of each cycle.The Cycle I forms a post-orogenic intraplate bimodal volcanic association.The cyclesⅡandⅢinclude arc volcanic associations formed in compressional and extensional subduction environments,respectively.The CycleⅣcontains a post-orogenic arc bimodal association.The CycleⅤis a basaltic association of tholeiite series under initial rift setting,and the CycleⅥis basaltic association of alkaline series under typical rift setting.The volcanic strata between each cycle are bounded by regional unconformity.The above 6 volcanic cycles correspond to 6 sequential stages of tectonic evolutions from the Early Jurassic post-orogeny,the Mid-Jurassic–Cretaceous subduction of the paleo-Pacific Plate to the Cenozoic marginal rifting.According to the geological characteristics of volcanic reservoirs in different volcanic cycles,it is put forward that the CycleⅤis the major formation period of volcanic reservoirs in East China and should be the focus of exploration,and that the volcanic reservoirs of the CycleⅣare also worthy of attention.
