The Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LM...The Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LMCC experienced two-stage extension. The ductile regime experienced top-to-northeast shearing extension and the brittle detachment fault underwent top-down-outwards slipping. Between these two stages, a semi-ductile regime recorded the transition from ductile to brittle. The hanging wall of the detachment fault is similar to those classic supradetachment basins in western North America. Analyses of provenance and paleocurrent directions in the basins show that there were two filling stages. In the early stage, materials came from the southwest margin of the basin and the hanging wall of the detachment system and were transported from southwest to northeast; while in the late stage, deposits were derived from the footwall of the detachment fault and transported outwards to the two sides of the core complex. Since the filling period of the basins is from the late Jurassic to the late Cretaceous and it is coeval with the extension, the two filling stages reflect the two-stage history of the detachment fault. The large-scale late Jurassic underplating in the deep crust of the Chifeng area led to thickening and heating of the middle-upper crust and trigged the extension at depths and volcanism on the surface. In the early Cretaceous the upper plate of the detachment fault moved northeastwards and sediments were transported from southwest to northeast, while in the late Cretaceous the core complex was uplifted rapidly, the original basin was separated by the uplifted core, and lower-plate-derived debris was deposited in the adjacent upper-plate basins of the detachment fault. Evidentially, the development of the supradetachment basins were controlled by the extension and in turn the fillings in the basins recorded information of the extension, which has provided new evidence for kinematic interpretation of the Louzidian core complex.展开更多
Radar remote sensing can acquire information of sub-surface covered by sand in arid area, detect surface roughness and vegetation coronet's layer and linear feature such as linear structure and channel sensitively...Radar remote sensing can acquire information of sub-surface covered by sand in arid area, detect surface roughness and vegetation coronet's layer and linear feature such as linear structure and channel sensitively. With sediment facies analysis, this paper studies the features of environmental evolution in mid-late Epipleistocene (60 ka BP-20 ka BP) in northeastern Ejin Banner. The conclusions are listed as follows: (1) The evolution of the three lakes, i.e. Gaxunnur, Sugunur and Tian'e lakes, are dominated by faults and regional climate. (2) By analyzing sedimentary section of old Juyanze Lake, the three lakes used to be a large outflow lake before 50 ka BP in northeastern Ejin Banner, and at 50 ka BP, temperature declined rapidly in northwestern China. The event caused the lake's shrinkage. (3) By fault activity uplift in the northern part of old Juyan Lake and depression in the southern part, the lake's water followed from north to south at around 35 ka BP, old Juyanze fluvial fan was formed. At the same time, Juyan Lake separated from Sugunur Lake and Wentugunr old channel was abandoned. (4) In recent 2000 years, Ruoshui River is a wandering river, sometimes it flows into Juyan Lake and sometimes Sugunur and Gaxunnur lakes. Due to human activities and over exploitation, the oasis ecosystem is rapidly degenerated in 15 years (1986-2000).展开更多
Petrologic geochemistry and isotopic chronology of the eclogites sug ge st that most of the eclogites in northern Dabie Mountains produced from the Tria ssic Yangtze subducted continental crust (lower crust and formed...Petrologic geochemistry and isotopic chronology of the eclogites sug ge st that most of the eclogites in northern Dabie Mountains produced from the Tria ssic Yangtze subducted continental crust (lower crust and formed during the deep subduction) and the metamorphosed mafic untramafic belt with eclogite, marble and meta peridotite blocks around the Mozitan Xiaotian fault zone may represen t the meta tectonic melange produced during the active subduction of an ancient oceanic slab and subsequent collision between the Yangtze and North China conti nental plates. The cooling history of the eclogites from ～900 ℃ to 300 ℃ can b e subdivided into three stages: one isothermal stage and two rapid cooling stage s. The initial stage between (230±6) and 210 Ma was a near isothermal or tempe rature rise process corresponding to the retrograded metamorphism of granulite facies with a rapid uplift of 4 mm/a, then two fast cooling stages occurred with cooling rate of ～10 ℃/Ma during 210 Ma to (172±3) Ma and ～4 ℃/Ma durin g (172±3) Ma to 130 Ma. After the peak metamorphism of eclogite facies, their in itial isothermal stage with slower uplift rate and cooling rate and high T overprinting of granulite facies metamorphism is the major difference between t he eclogites in northern Dabie Mountains from those in southern Dabie Mountains. This may be one of the most important reasons to preserve few evidences of earl ier ultrahigh pressure metamorphism.展开更多
Using a 2.5-dimensional (2.5-D) ideal MHD model, this paper analyzes the equilibrium properties of coronal magnetic flux ropes in a bipolar ambient magnetic field. It is found that the geometrical features of the mag...Using a 2.5-dimensional (2.5-D) ideal MHD model, this paper analyzes the equilibrium properties of coronal magnetic flux ropes in a bipolar ambient magnetic field. It is found that the geometrical features of the magnetic flux rope, including the height of the rope axis, the half-width of the ropes and the length of the vertical current sheet below the ropes are determined by a single magnetic parameter, the magnetic helicity, which is the sum of the self-helicity of the rope and the mutual helicity between the rope field and the ambient magnetic field. All the geometrical parameters increase monotonically with increasing magnetic helicity. The implication of this result in solar active phenomena is briefly discussed.展开更多
An 18--year-long (1981-1998) study was conducted in Hainan Island waters (22°20’N, 110°39’E) to determine the relationship between 618O in skeletal aragonite carbonate and sea surface temperature (SST) in ...An 18--year-long (1981-1998) study was conducted in Hainan Island waters (22°20’N, 110°39’E) to determine the relationship between 618O in skeletal aragonite carbonate and sea surface temperature (SST) in porites lutea of reef-building corals. 618O values in skeletal aragonite carbonate were measured by means of mass spectrometry. Coral samples grew at sin depth at Longwan Bay. Monthly measurements of the SST from 1960 to 1998 were taken at Qinglan Buy adjacent to the place of the collected samples. The thermometer shows that SST=-4.16 б~18O_PDB + 4.9 (r=0.80) and dб~18O/dT=-0.24 permil/°C. The б~18O thermometer is strongly influenced by the rainfall and runoff. Using the thermometer, the SST in the past hundred years with monthly resolution will be reconstructed and the climatic change in the northern area of South China Sea will be展开更多
He and Ar isotopic compositions of megacrystal minerals from mantle xenoliths were measured by the technique of vacuum crushing extraction. The used samples were clinopyroxene, garnet and ilmenite in Cenozoic alkaline...He and Ar isotopic compositions of megacrystal minerals from mantle xenoliths were measured by the technique of vacuum crushing extraction. The used samples were clinopyroxene, garnet and ilmenite in Cenozoic alkaline basalts, which were from Nushan in Anhui Province and Yingfengling in Guangdong Province, respectively, and represented materials from the upper mantle in the continental margin of SE China. The results show 3He/4He ratios of 7.99 Ra to 8.58 Ra, consistent with the characteristic ratios of the MORB-type mantle. 40Ar/39Ar ratios vary from 313 to 909, suggesting a binary mixing between the MORB-type mantle and air argons. This may reflect the incorporation of the air argon absorbed in oceanic sediments into the mantle beneath the continental margin by subduction of oceanic plate. This study presents the first report that ilmenite megacrysts contain abundant fluid inclusions and noble gases in the mantle xenoliths.展开更多
Based on the comparison of dating results among high-precision TIMS U-series and AMS 14C as well as the published 14C dating results and their band counting ages (i.e. calendar ages), this paper discusses the effect o...Based on the comparison of dating results among high-precision TIMS U-series and AMS 14C as well as the published 14C dating results and their band counting ages (i.e. calendar ages), this paper discusses the effect of dead carbon on the speleothem 14C dating. The result shows that the fraction of incorporated dead carbon during the forma- tion of speleothem varies. The change in the fraction of dead carbon would result in big deviation in the 14C age of the speleothem. It is indispensable to take the dead carbon into consideration when dating the speleothem using the 14C method or studying the atmospheric 14C concentration dur- ing the past with the speleothem.展开更多
基金supported by the National Natural Science Foundation of China(grant 40102017)the Doctoral Program of Higher Education(grant 2000000128).
文摘The Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LMCC experienced two-stage extension. The ductile regime experienced top-to-northeast shearing extension and the brittle detachment fault underwent top-down-outwards slipping. Between these two stages, a semi-ductile regime recorded the transition from ductile to brittle. The hanging wall of the detachment fault is similar to those classic supradetachment basins in western North America. Analyses of provenance and paleocurrent directions in the basins show that there were two filling stages. In the early stage, materials came from the southwest margin of the basin and the hanging wall of the detachment system and were transported from southwest to northeast; while in the late stage, deposits were derived from the footwall of the detachment fault and transported outwards to the two sides of the core complex. Since the filling period of the basins is from the late Jurassic to the late Cretaceous and it is coeval with the extension, the two filling stages reflect the two-stage history of the detachment fault. The large-scale late Jurassic underplating in the deep crust of the Chifeng area led to thickening and heating of the middle-upper crust and trigged the extension at depths and volcanism on the surface. In the early Cretaceous the upper plate of the detachment fault moved northeastwards and sediments were transported from southwest to northeast, while in the late Cretaceous the core complex was uplifted rapidly, the original basin was separated by the uplifted core, and lower-plate-derived debris was deposited in the adjacent upper-plate basins of the detachment fault. Evidentially, the development of the supradetachment basins were controlled by the extension and in turn the fillings in the basins recorded information of the extension, which has provided new evidence for kinematic interpretation of the Louzidian core complex.
文摘Radar remote sensing can acquire information of sub-surface covered by sand in arid area, detect surface roughness and vegetation coronet's layer and linear feature such as linear structure and channel sensitively. With sediment facies analysis, this paper studies the features of environmental evolution in mid-late Epipleistocene (60 ka BP-20 ka BP) in northeastern Ejin Banner. The conclusions are listed as follows: (1) The evolution of the three lakes, i.e. Gaxunnur, Sugunur and Tian'e lakes, are dominated by faults and regional climate. (2) By analyzing sedimentary section of old Juyanze Lake, the three lakes used to be a large outflow lake before 50 ka BP in northeastern Ejin Banner, and at 50 ka BP, temperature declined rapidly in northwestern China. The event caused the lake's shrinkage. (3) By fault activity uplift in the northern part of old Juyan Lake and depression in the southern part, the lake's water followed from north to south at around 35 ka BP, old Juyanze fluvial fan was formed. At the same time, Juyan Lake separated from Sugunur Lake and Wentugunr old channel was abandoned. (4) In recent 2000 years, Ruoshui River is a wandering river, sometimes it flows into Juyan Lake and sometimes Sugunur and Gaxunnur lakes. Due to human activities and over exploitation, the oasis ecosystem is rapidly degenerated in 15 years (1986-2000).
文摘Petrologic geochemistry and isotopic chronology of the eclogites sug ge st that most of the eclogites in northern Dabie Mountains produced from the Tria ssic Yangtze subducted continental crust (lower crust and formed during the deep subduction) and the metamorphosed mafic untramafic belt with eclogite, marble and meta peridotite blocks around the Mozitan Xiaotian fault zone may represen t the meta tectonic melange produced during the active subduction of an ancient oceanic slab and subsequent collision between the Yangtze and North China conti nental plates. The cooling history of the eclogites from ～900 ℃ to 300 ℃ can b e subdivided into three stages: one isothermal stage and two rapid cooling stage s. The initial stage between (230±6) and 210 Ma was a near isothermal or tempe rature rise process corresponding to the retrograded metamorphism of granulite facies with a rapid uplift of 4 mm/a, then two fast cooling stages occurred with cooling rate of ～10 ℃/Ma during 210 Ma to (172±3) Ma and ～4 ℃/Ma durin g (172±3) Ma to 130 Ma. After the peak metamorphism of eclogite facies, their in itial isothermal stage with slower uplift rate and cooling rate and high T overprinting of granulite facies metamorphism is the major difference between t he eclogites in northern Dabie Mountains from those in southern Dabie Mountains. This may be one of the most important reasons to preserve few evidences of earl ier ultrahigh pressure metamorphism.
基金Major Project 19791090 supported by National Natural Science Foundation of China and 973 Project (G2000078404).
文摘Using a 2.5-dimensional (2.5-D) ideal MHD model, this paper analyzes the equilibrium properties of coronal magnetic flux ropes in a bipolar ambient magnetic field. It is found that the geometrical features of the magnetic flux rope, including the height of the rope axis, the half-width of the ropes and the length of the vertical current sheet below the ropes are determined by a single magnetic parameter, the magnetic helicity, which is the sum of the self-helicity of the rope and the mutual helicity between the rope field and the ambient magnetic field. All the geometrical parameters increase monotonically with increasing magnetic helicity. The implication of this result in solar active phenomena is briefly discussed.
基金NKBRSF Project Fund (G1999043401), National Natural Science Fundation(49776307), The innovation Project Fund of Chinese Academ
文摘An 18--year-long (1981-1998) study was conducted in Hainan Island waters (22°20’N, 110°39’E) to determine the relationship between 618O in skeletal aragonite carbonate and sea surface temperature (SST) in porites lutea of reef-building corals. 618O values in skeletal aragonite carbonate were measured by means of mass spectrometry. Coral samples grew at sin depth at Longwan Bay. Monthly measurements of the SST from 1960 to 1998 were taken at Qinglan Buy adjacent to the place of the collected samples. The thermometer shows that SST=-4.16 б~18O_PDB + 4.9 (r=0.80) and dб~18O/dT=-0.24 permil/°C. The б~18O thermometer is strongly influenced by the rainfall and runoff. Using the thermometer, the SST in the past hundred years with monthly resolution will be reconstructed and the climatic change in the northern area of South China Sea will be
基金supported by The National Natural Science Foundation of China(Grant Nos.49473175,49972062 and 40110104104).
文摘He and Ar isotopic compositions of megacrystal minerals from mantle xenoliths were measured by the technique of vacuum crushing extraction. The used samples were clinopyroxene, garnet and ilmenite in Cenozoic alkaline basalts, which were from Nushan in Anhui Province and Yingfengling in Guangdong Province, respectively, and represented materials from the upper mantle in the continental margin of SE China. The results show 3He/4He ratios of 7.99 Ra to 8.58 Ra, consistent with the characteristic ratios of the MORB-type mantle. 40Ar/39Ar ratios vary from 313 to 909, suggesting a binary mixing between the MORB-type mantle and air argons. This may reflect the incorporation of the air argon absorbed in oceanic sediments into the mantle beneath the continental margin by subduction of oceanic plate. This study presents the first report that ilmenite megacrysts contain abundant fluid inclusions and noble gases in the mantle xenoliths.
基金supported by the Chinese Academy of Sciences(Grant Nos.KZCX2-SW-118 and KZCX3-SW-120)the National Basic Research Program of China(Grant No.G1 999043401).
文摘Based on the comparison of dating results among high-precision TIMS U-series and AMS 14C as well as the published 14C dating results and their band counting ages (i.e. calendar ages), this paper discusses the effect of dead carbon on the speleothem 14C dating. The result shows that the fraction of incorporated dead carbon during the forma- tion of speleothem varies. The change in the fraction of dead carbon would result in big deviation in the 14C age of the speleothem. It is indispensable to take the dead carbon into consideration when dating the speleothem using the 14C method or studying the atmospheric 14C concentration dur- ing the past with the speleothem.
