Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits(the Xiashu loess)in the lower reaches of the Yangtze River.Both a local source from the fluvial sedimen...Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits(the Xiashu loess)in the lower reaches of the Yangtze River.Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau(CLP)have been proposed.Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique.This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess.The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior.Instead,the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River,indicating the dominance of proximal dust source.Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China,possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.展开更多
SHRIMP U-Pb zircon 207 Pb/206 Pb ages were obtained from two drill cores from the basement of the Ordos Basin.A garnet-sillimanite-biotite-plagioclase gneiss(QI1-1) from the western Ordos Basin basement yielded an ave...SHRIMP U-Pb zircon 207 Pb/206 Pb ages were obtained from two drill cores from the basement of the Ordos Basin.A garnet-sillimanite-biotite-plagioclase gneiss(QI1-1) from the western Ordos Basin basement yielded an average age of 2031 10 Ma.Based on the mineral assemblages,the source material of the gneiss is speculated to be pelitic-felsic system.A gneissic two-mica granite(Long1-1) from the eastern Ordos Basin basement yielded an average age of 2035 10 Ma.The zircons from both samples exhibit magmatic growth pattern.The shapes of the zircons suggest that the zircons should crystallize from a granitic of felsic volcanic terrain.The ages and the characters of zircons are consisitent with the other researches in the Ordos Basin and indicate that the basement of the Ordos Basin had experienced an intensive magmatic epsode during the late Paleoproterozoic period.The date from this study suggest the possible existences of a Paleoproterozoic mobile tectonic belt in the region.The reconstruction of such a belt is critical for understanding the tectonomagmatic evolution of the western block of the North China Craton.展开更多
Clastic sediments and sedimentary rocks are widely used for understanding the formation and evolution of the continental crust.The Tietonggou Formation outcrops in the Xiaoqinling region at the southern margin of the ...Clastic sediments and sedimentary rocks are widely used for understanding the formation and evolution of the continental crust.The Tietonggou Formation outcrops in the Xiaoqinling region at the southern margin of the North China Craton(NCC)and has unconformable contacts with the underlying Taihua Complex and overlying Paleoproterozoic Xiong’er Group.It mainly consists of quartzite and its protoliths are mature terrigenous clastic rocks.On the basis of the ages of the youngest detrital zircons from the quartzites and the ages of the Xiong’er Group,the depositional ages of the protoliths of the Tietonggou Formation were well constrained to 1.91–1.80 Ga.The U-Pb isotopic data of detrital zircons from the Formation show a major age peak at^2.1 Ga,which is consistent with 2.2–2.0 Ga magmatism in the Trans-North China Orogen of the NCC.Taking into account the texctural and compositional maturity of the Tietonggou Formation quartzite,the^2.1 Ga lithologic units in the Trans-North China Orogen are interpreted as the major source of the Tietonggou Formation.The majority of these^2.1 Ga detrital zircons mostly have highδ18O values(>6.5‰)and negativeεHf(t)values(–7.8–0.0),with corresponding Hf model ages significantly older than their crystallization ages,indicating that these zircons formed from the partial melting of ancient continental crust.The majority of the2.8–2.7 Ga and^2.5 Ga detrital zircons from the Tietonggou Formation had positiveεHf(t)values,and mantle-likeδ18O values,suggesting that the NCC has experienced two stages of significant crustal growth in the Neoarchaean at 2.7 and 2.5 Ga,respectively.The Hf isotopic data of detrital zircons from Paleoproterozoic metasedimentary rocks in the Trans-North China Orogen varied mainly toward the reduction of the radiogenic Hf isotope and gradually show a similar trend of the isotope trajectories of crustal evolution.This reveals that the NCC probably has not developed a long-lived subduction to complete the final assembly of the NCC.Alternatively,the展开更多
By means of multi-dimensional regression analysis the author proposes for the first time the concept of “isochron plane” and develops two methods for solving three-stage U-Pb equations. Evolution of Nanling granites...By means of multi-dimensional regression analysis the author proposes for the first time the concept of “isochron plane” and develops two methods for solving three-stage U-Pb equations. Evolution of Nanling granites, metamorphic rocks fromthe Liaotung Peninsula and lunar basalts from Ocean Procellarum has been discussed in the light of U-Pb three.stage model calculations. The U-Pb third-stage modcl ages for these rocks are consistent with their K-Ar or Rb-Sr ages as well as with geological field observations.展开更多
基金supported by the National Natural Science Foundation of China(41102103,41173105 and 41321062)
文摘Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits(the Xiashu loess)in the lower reaches of the Yangtze River.Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau(CLP)have been proposed.Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique.This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess.The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior.Instead,the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River,indicating the dominance of proximal dust source.Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China,possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.
基金supported by the National Basic Research Program of China (2012CB416604 and 2012CB416603)the National Natural Science Foundation of China (91114204)
文摘SHRIMP U-Pb zircon 207 Pb/206 Pb ages were obtained from two drill cores from the basement of the Ordos Basin.A garnet-sillimanite-biotite-plagioclase gneiss(QI1-1) from the western Ordos Basin basement yielded an average age of 2031 10 Ma.Based on the mineral assemblages,the source material of the gneiss is speculated to be pelitic-felsic system.A gneissic two-mica granite(Long1-1) from the eastern Ordos Basin basement yielded an average age of 2035 10 Ma.The zircons from both samples exhibit magmatic growth pattern.The shapes of the zircons suggest that the zircons should crystallize from a granitic of felsic volcanic terrain.The ages and the characters of zircons are consisitent with the other researches in the Ordos Basin and indicate that the basement of the Ordos Basin had experienced an intensive magmatic epsode during the late Paleoproterozoic period.The date from this study suggest the possible existences of a Paleoproterozoic mobile tectonic belt in the region.The reconstruction of such a belt is critical for understanding the tectonomagmatic evolution of the western block of the North China Craton.
基金supported by the National Basic Research Program of China(2012CB416606)the National Natural Science Foundation of China(41272004)the MOST Special Funds from the State Key Laboratory of Continental Dynamics
文摘Clastic sediments and sedimentary rocks are widely used for understanding the formation and evolution of the continental crust.The Tietonggou Formation outcrops in the Xiaoqinling region at the southern margin of the North China Craton(NCC)and has unconformable contacts with the underlying Taihua Complex and overlying Paleoproterozoic Xiong’er Group.It mainly consists of quartzite and its protoliths are mature terrigenous clastic rocks.On the basis of the ages of the youngest detrital zircons from the quartzites and the ages of the Xiong’er Group,the depositional ages of the protoliths of the Tietonggou Formation were well constrained to 1.91–1.80 Ga.The U-Pb isotopic data of detrital zircons from the Formation show a major age peak at^2.1 Ga,which is consistent with 2.2–2.0 Ga magmatism in the Trans-North China Orogen of the NCC.Taking into account the texctural and compositional maturity of the Tietonggou Formation quartzite,the^2.1 Ga lithologic units in the Trans-North China Orogen are interpreted as the major source of the Tietonggou Formation.The majority of these^2.1 Ga detrital zircons mostly have highδ18O values(>6.5‰)and negativeεHf(t)values(–7.8–0.0),with corresponding Hf model ages significantly older than their crystallization ages,indicating that these zircons formed from the partial melting of ancient continental crust.The majority of the2.8–2.7 Ga and^2.5 Ga detrital zircons from the Tietonggou Formation had positiveεHf(t)values,and mantle-likeδ18O values,suggesting that the NCC has experienced two stages of significant crustal growth in the Neoarchaean at 2.7 and 2.5 Ga,respectively.The Hf isotopic data of detrital zircons from Paleoproterozoic metasedimentary rocks in the Trans-North China Orogen varied mainly toward the reduction of the radiogenic Hf isotope and gradually show a similar trend of the isotope trajectories of crustal evolution.This reveals that the NCC probably has not developed a long-lived subduction to complete the final assembly of the NCC.Alternatively,the
文摘By means of multi-dimensional regression analysis the author proposes for the first time the concept of “isochron plane” and develops two methods for solving three-stage U-Pb equations. Evolution of Nanling granites, metamorphic rocks fromthe Liaotung Peninsula and lunar basalts from Ocean Procellarum has been discussed in the light of U-Pb three.stage model calculations. The U-Pb third-stage modcl ages for these rocks are consistent with their K-Ar or Rb-Sr ages as well as with geological field observations.
