Previous studies have shown that the Archean basement is widely distributed throughout the Yangtze craton. To date, however, Archean basement terrains have not been found, except for a few Kongling high-grade metamorp...Previous studies have shown that the Archean basement is widely distributed throughout the Yangtze craton. To date, however, Archean basement terrains have not been found, except for a few Kongling high-grade metamorphic terrains in the Huangling dome that have been confirmed to be of Archean age. To further understand the basement component and crustal evolution of the Yangtze craton, we carried out a petrological, geochronological and geochemical study of the Jinshan K-feldspar granite emplaced within the Yangpo Group, located in Huji Town, Zhongxiang City, Hubei Province. Results indicate that the zircon SHRIMP U-Pb age of the Jinshan granite is 2655±9 Ma, placing it within the middle Neoarchean. Chemically, this pluton yields abundant silica and alkalis and is depleted in Ca, Mg and Ti. Furthermore, it is enriched in Rb, Th, Ga, Y and Zr, depleted in Sr, Ba, Nb and Ta, and especially lacking in Eu. High ratios of FeO*/MgO (32.0 to 58.7) and 104 ×Ga/Al (3.19 to 3.41) were also found. The pluton exhibits characteristics typical of A-type granites with crustal source magmas. Moreover, the meta-sedimentary rock association of the Yangpo Group, into which the pluton intruded, clearly shows relatively stable depositional environments of a shallow shelf sequence. Therefore, before the middle Neoarchean, the Yangtze craton contained mature continental crust. This breakthrough discovery opens a new window on the study of the formation and evolution of the Yangtze craton basement.展开更多
Zircon U-Pb ages(SHRIMP and LA-ICPMS) and Lu-Hf isotope data(LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai...Zircon U-Pb ages(SHRIMP and LA-ICPMS) and Lu-Hf isotope data(LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai Mountains area in the North China Craton.These two granite pebbles give zircon 207 Pb/206 Pb ages of 2513±8 Ma and 2527±8 Ma respectively,which are consistent with the emplacement ages of the Wangjiahui grey granite and Guangmingsi or Shifo granite in the Wutai Mountains.Detrital zircons from those two quartzite pebbles are mostly 2550-2490 Ma old with lesser number of 2800-2550 Ma grains,which is similar to the ages of detrital zircons from quartzites in the Gaofan Subgroup of the Neoarchean Wutai Group.Thus,the pebbles in the Hutuo Group basal conglomerates were derived locally from Wutai Mountains Neoarchean sources.Zircons from the Sijizhuang Formation conglomerate granite and quartzite pebbles mostly have positive ε Hf(t) values,a minority with ε Hf(t) values like model depleted mantle(DM) of the same age,but with most showing DM model ages 200-100 Ma.This indicates that most of the source materials were derived from the mantle within the previous 200 million years,whereas some are derived from 2550-2510 Ma juvenile crustal additions.This additional evidence suggests that in the North China Craton there was important initial polycyclic crustal formation and cratonization in the late Neoarchaean,prior to superimposed Palaeoproterozoic orogenic cycles.展开更多
Cratonization is a key geological process to form stable continental masses with a considerable scale.The Precambrian global cratonization and formation of supercratons in the world is an unrepeated event in the histo...Cratonization is a key geological process to form stable continental masses with a considerable scale.The Precambrian global cratonization and formation of supercratons in the world is an unrepeated event in the history of the Earth's formation and evolution.Mainly based on study of early Precambrian geology in Eastern Hebei Region and combining other Archean regions in the North China Craton (NCC),the author proposes a two-stage cratonization model of the NCC.The first stage took place at the end of Neoarchean of ～2.5 Ga (boundary time between Archean and Proterozoic),when several micro-blocks were amalgamated together with amphibolite-granulite facies metamorphism and intrusion of crustal-melting granites to form the present-scale NCC.The second cratonization event is cratonic reworking,corresponding to rifting-subduction-collision at 2.3-1.97 Ga and subsequent extension-uplifting related to upwelling mantle at 1.97-1.82 Ga,which could be linked to,respectively,assembly and breaking up of the Columbia Supercontinent.Three main Paleoproterozoic mobile belts in the NCC record that small remnant Neoarchean ocean basins and continental rift basins within the craton were opened and finally closed,and metamorphosed to greenschist-amphibolite facies at ～2.0-1.97 Ga.After that,high-grade granulite facies (HT-HP and HT-UHT) metamorphism with abnormally high heat occurred at 1.97-1.82 Ga.A metamorphism-migmatization event that includes lower crust of the NCC uplifting as a whole,intrusion of mafic dyke swarms,continental rifting and anorogenic magmatic action took place in 1.82-1.65 Ga,marking that the second cratonization of the NCC was finally accomplished and started to evolve to a period of stable continent (platform).展开更多
基金supported by the National Natural Science Foundation of China (41030315 and 41072088)the Chinese Geological Survey (1212011121111 and 1212011220750)
文摘Previous studies have shown that the Archean basement is widely distributed throughout the Yangtze craton. To date, however, Archean basement terrains have not been found, except for a few Kongling high-grade metamorphic terrains in the Huangling dome that have been confirmed to be of Archean age. To further understand the basement component and crustal evolution of the Yangtze craton, we carried out a petrological, geochronological and geochemical study of the Jinshan K-feldspar granite emplaced within the Yangpo Group, located in Huji Town, Zhongxiang City, Hubei Province. Results indicate that the zircon SHRIMP U-Pb age of the Jinshan granite is 2655±9 Ma, placing it within the middle Neoarchean. Chemically, this pluton yields abundant silica and alkalis and is depleted in Ca, Mg and Ti. Furthermore, it is enriched in Rb, Th, Ga, Y and Zr, depleted in Sr, Ba, Nb and Ta, and especially lacking in Eu. High ratios of FeO*/MgO (32.0 to 58.7) and 104 ×Ga/Al (3.19 to 3.41) were also found. The pluton exhibits characteristics typical of A-type granites with crustal source magmas. Moreover, the meta-sedimentary rock association of the Yangpo Group, into which the pluton intruded, clearly shows relatively stable depositional environments of a shallow shelf sequence. Therefore, before the middle Neoarchean, the Yangtze craton contained mature continental crust. This breakthrough discovery opens a new window on the study of the formation and evolution of the Yangtze craton basement.
基金supported by China Geological Survey (Grant Nos. 1212010611802,1212010711815 and 1212011120152)National Natural Science Foundation of China (Grant No. 41172171)+1 种基金Basic Foundation of Scientific Research Work from Ministry of Science and Technology of China (GrantNos. J0721 and J0907)National Commission on Stratigraphy of China(Grant Nos. 1212010511702-01 and 1212011120142)
文摘Zircon U-Pb ages(SHRIMP and LA-ICPMS) and Lu-Hf isotope data(LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai Mountains area in the North China Craton.These two granite pebbles give zircon 207 Pb/206 Pb ages of 2513±8 Ma and 2527±8 Ma respectively,which are consistent with the emplacement ages of the Wangjiahui grey granite and Guangmingsi or Shifo granite in the Wutai Mountains.Detrital zircons from those two quartzite pebbles are mostly 2550-2490 Ma old with lesser number of 2800-2550 Ma grains,which is similar to the ages of detrital zircons from quartzites in the Gaofan Subgroup of the Neoarchean Wutai Group.Thus,the pebbles in the Hutuo Group basal conglomerates were derived locally from Wutai Mountains Neoarchean sources.Zircons from the Sijizhuang Formation conglomerate granite and quartzite pebbles mostly have positive ε Hf(t) values,a minority with ε Hf(t) values like model depleted mantle(DM) of the same age,but with most showing DM model ages 200-100 Ma.This indicates that most of the source materials were derived from the mantle within the previous 200 million years,whereas some are derived from 2550-2510 Ma juvenile crustal additions.This additional evidence suggests that in the North China Craton there was important initial polycyclic crustal formation and cratonization in the late Neoarchaean,prior to superimposed Palaeoproterozoic orogenic cycles.
基金supported by National Natural Science Foundation of China(Grant Nos.41030316,90714003)Chinese Academy of Sciences(Grant No.KZCX2-YW-Q04-04)
文摘Cratonization is a key geological process to form stable continental masses with a considerable scale.The Precambrian global cratonization and formation of supercratons in the world is an unrepeated event in the history of the Earth's formation and evolution.Mainly based on study of early Precambrian geology in Eastern Hebei Region and combining other Archean regions in the North China Craton (NCC),the author proposes a two-stage cratonization model of the NCC.The first stage took place at the end of Neoarchean of ～2.5 Ga (boundary time between Archean and Proterozoic),when several micro-blocks were amalgamated together with amphibolite-granulite facies metamorphism and intrusion of crustal-melting granites to form the present-scale NCC.The second cratonization event is cratonic reworking,corresponding to rifting-subduction-collision at 2.3-1.97 Ga and subsequent extension-uplifting related to upwelling mantle at 1.97-1.82 Ga,which could be linked to,respectively,assembly and breaking up of the Columbia Supercontinent.Three main Paleoproterozoic mobile belts in the NCC record that small remnant Neoarchean ocean basins and continental rift basins within the craton were opened and finally closed,and metamorphosed to greenschist-amphibolite facies at ～2.0-1.97 Ga.After that,high-grade granulite facies (HT-HP and HT-UHT) metamorphism with abnormally high heat occurred at 1.97-1.82 Ga.A metamorphism-migmatization event that includes lower crust of the NCC uplifting as a whole,intrusion of mafic dyke swarms,continental rifting and anorogenic magmatic action took place in 1.82-1.65 Ga,marking that the second cratonization of the NCC was finally accomplished and started to evolve to a period of stable continent (platform).
