The mafic dykes from the Paleoproterozoic Bomdila Group of metasedimentary rocks,Arunachal Pradesh,NE Lesser Himalaya,India have been analyzed for major and trace elements geochemistry essentially to understand their
The Sr, Nd and Pb isotopic characteristics of the Wudang basic dyke swarms and basic volcanics of the Yaolinghe Group show that they were derived from the same multi\|component mixing source in the mantle. The Wudang ...The Sr, Nd and Pb isotopic characteristics of the Wudang basic dyke swarms and basic volcanics of the Yaolinghe Group show that they were derived from the same multi\|component mixing source in the mantle. The Wudang basic dyke swarms have (\{\}\+\{87\}Sr/\{\}\+\{86\}Sr)\-i=\{0.6905\}～\{0.7061\}, ε\-\{Nd\}(t)=\{-1.9\}～\{5.0\}, Δ\{\}\+\{208\}Pb/\+\{204\}Pb=\{35.49\}～\{190.26\}, Δ\{\}\+\{207\}Pb/\{\}\+\{204\}Pb=4～85, low Th/Ta and a wide range of La/Yb ratios; and the basic volcanics of the Yaolinghe Group have (\{\}\+\{87\}Sr/\{\}\+\{86\}Sr)\-i=\{0.6487\}～\{0.7075\}, ε\-\{Nd\}(t)=\{0.11\}～\{3.94\}, Δ\{\}\+\{208\}Pb/\{\}\+\{204\}Pb=\{-81.58\}～\{219.95\}, Δ\{\}\+\{207\}Pb/\{\}\+\{204\}Pb=\{4.44\}～\{16.68\} and higher Th/Ta and La/Yb ratios, indicating that their source is a mixture of DM and EMII, and the basic volcanics of the Yaolinghe Group were contaminated by crust materials en rout to the surface. Based on the geochemical features of continental tholeiitic basalts and being products of different facies derived from the same source, it can be concluded that an important rifting event in the South Qinling basement block occurred during Neoproterozoic, followed by a setting of oceanic basin in the Early Paleozoic.展开更多
A group of NE-trending(～30°)mafic dykes,termed Miyun swarm herein,are distributed around the Miyun Reservoir,northe China,and have individual widths of over 40 m,and lengths of up to 8000 m.Baddeleyite grains we...A group of NE-trending(～30°)mafic dykes,termed Miyun swarm herein,are distributed around the Miyun Reservoir,northe China,and have individual widths of over 40 m,and lengths of up to 8000 m.Baddeleyite grains were extracted from a～40 wide dyke.Using an isotope dilution thermal ionization mass spectrometry method,these grains yield an average 207Pb/206Pb a of 1731±4 Ma(n=4;or 1731±1 Ma,n=3).Because this dyke is overlain unconformably by conglomerates of the Changzhoug Formation,the lowermost formation of the Changcheng Group,the maximum depositional age of this group is constrained to no earlier than 1731 Ma.This result also suggests that the Changcheng System,with the Changcheng Group as its standard stra graphic section,is younger than 1731 Ma.The Miyun dykes possibly have distinct petrogenesis from the subsequent anorth site-rapakivi intrusions(1730-1680 Ma),which are thought to be responsible for the opening of the Yan-Liao rift,where Changcheng Group was deposited.Thus it is reasonable to set the initial boundary of the Changchengian Period at 1730 Ma slightly younger.展开更多
This paper presents the studies on groundwater resources potential of the Yellow River (YR) terrace in Zhengzhou area, China. The main aim of the research was to resolve water shortage problems induced by recent but f...This paper presents the studies on groundwater resources potential of the Yellow River (YR) terrace in Zhengzhou area, China. The main aim of the research was to resolve water shortage problems induced by recent but frequent drying ups of the YR in its lower reaches. Geologic explorations and grouped-pumping tests were conducted in the area. Based on collected data a groundwater flow net was established. The buried depth of groundwater level and water bearing potential of the aquifers were evaluated. Conventional method was used to determine recharge of the groundwater by lateral infiltration of the YR in pumping patterns. The results show that the study region has a high water bearing potential and offers conditions for the construction of large water works. However, only limited recharge by lateral infiltration from the river is available when developing large scale groundwater exploitation in the riverside of the YR. Environmental impacts induced by embankment stability of the Great dyke of the YR could be minimized or eliminated by appropriate engineering methods.展开更多
文摘The mafic dykes from the Paleoproterozoic Bomdila Group of metasedimentary rocks,Arunachal Pradesh,NE Lesser Himalaya,India have been analyzed for major and trace elements geochemistry essentially to understand their
文摘The Sr, Nd and Pb isotopic characteristics of the Wudang basic dyke swarms and basic volcanics of the Yaolinghe Group show that they were derived from the same multi\|component mixing source in the mantle. The Wudang basic dyke swarms have (\{\}\+\{87\}Sr/\{\}\+\{86\}Sr)\-i=\{0.6905\}～\{0.7061\}, ε\-\{Nd\}(t)=\{-1.9\}～\{5.0\}, Δ\{\}\+\{208\}Pb/\+\{204\}Pb=\{35.49\}～\{190.26\}, Δ\{\}\+\{207\}Pb/\{\}\+\{204\}Pb=4～85, low Th/Ta and a wide range of La/Yb ratios; and the basic volcanics of the Yaolinghe Group have (\{\}\+\{87\}Sr/\{\}\+\{86\}Sr)\-i=\{0.6487\}～\{0.7075\}, ε\-\{Nd\}(t)=\{0.11\}～\{3.94\}, Δ\{\}\+\{208\}Pb/\{\}\+\{204\}Pb=\{-81.58\}～\{219.95\}, Δ\{\}\+\{207\}Pb/\{\}\+\{204\}Pb=\{4.44\}～\{16.68\} and higher Th/Ta and La/Yb ratios, indicating that their source is a mixture of DM and EMII, and the basic volcanics of the Yaolinghe Group were contaminated by crust materials en rout to the surface. Based on the geochemical features of continental tholeiitic basalts and being products of different facies derived from the same source, it can be concluded that an important rifting event in the South Qinling basement block occurred during Neoproterozoic, followed by a setting of oceanic basin in the Early Paleozoic.
基金supported by the National Basic Research Programof China(2009CB219305)the National Natural Science Foundation of China(41072106)
文摘A group of NE-trending(～30°)mafic dykes,termed Miyun swarm herein,are distributed around the Miyun Reservoir,northe China,and have individual widths of over 40 m,and lengths of up to 8000 m.Baddeleyite grains were extracted from a～40 wide dyke.Using an isotope dilution thermal ionization mass spectrometry method,these grains yield an average 207Pb/206Pb a of 1731±4 Ma(n=4;or 1731±1 Ma,n=3).Because this dyke is overlain unconformably by conglomerates of the Changzhoug Formation,the lowermost formation of the Changcheng Group,the maximum depositional age of this group is constrained to no earlier than 1731 Ma.This result also suggests that the Changcheng System,with the Changcheng Group as its standard stra graphic section,is younger than 1731 Ma.The Miyun dykes possibly have distinct petrogenesis from the subsequent anorth site-rapakivi intrusions(1730-1680 Ma),which are thought to be responsible for the opening of the Yan-Liao rift,where Changcheng Group was deposited.Thus it is reasonable to set the initial boundary of the Changchengian Period at 1730 Ma slightly younger.
文摘This paper presents the studies on groundwater resources potential of the Yellow River (YR) terrace in Zhengzhou area, China. The main aim of the research was to resolve water shortage problems induced by recent but frequent drying ups of the YR in its lower reaches. Geologic explorations and grouped-pumping tests were conducted in the area. Based on collected data a groundwater flow net was established. The buried depth of groundwater level and water bearing potential of the aquifers were evaluated. Conventional method was used to determine recharge of the groundwater by lateral infiltration of the YR in pumping patterns. The results show that the study region has a high water bearing potential and offers conditions for the construction of large water works. However, only limited recharge by lateral infiltration from the river is available when developing large scale groundwater exploitation in the riverside of the YR. Environmental impacts induced by embankment stability of the Great dyke of the YR could be minimized or eliminated by appropriate engineering methods.
