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《Northwestern Geology》 2008-03
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Petrogenesis of the Yaolinghe Group,Yunxi Group,Wudangshan Group Volcanic Rocks and Basic Dyke Swarms from Eastern Part of the South Qinling Mountains

XIA Lin-qi,XIA Zu-chun,LI Xiang-min,MA Zhong-ping,XU Xue-yi(Xi'an Institute of Geology and Mineral Resources,Xi'an 710054,China)  
The mid-late Neoproterozoic(676~833 Ma) Yaolinghe Group,Yunxi Group,Wudangshan Group volcanic rocks and basic dyke swarms from eastern part of South Qinling Mountains produced an intracontinental rift setting.On the basis of geochemical data,the mid-late Neoproterozoic rift-related basic lavas and basic dykes from eastern part of South Qinling Mountains generally belong to a low Ti/Y(500) magma type.Elemental and isotopic data suggest that the chemical variations of the mid-late Neoproterozoic rift-related basic lavas and basic dykes from eastern part of South Qinling Mountains can not be explained by crystallization from a common parental magma.They most likely originated from a mantle plume source(εNd(t)≈+5,Mg≈0.7,La/Nb≈0.7).Continental crustal or continental lithosphere contamination has also contributed significantly to the formation of the mid-late Neoproterozoic rift-related basic lavas and basic dykes from eastern part of the South Qinling Mountains.Our data indicate that the spatial geochemical variations existed in the mid-late Neoproterozoic rift-related volcanic rocks and basic dykes from eastern part of South Qinling Mountains.They were generally generated in a mantle source within the garnet stability field.In contrast,in the northwestern Zhen’an area the parental magmas of the Yaolinghe Group basic lavas were generated from a mantle around the spinel-garnet transition zone.The alkaline lavas were generated by lower degrees(10%) of partial melting and the tholeiitic lavas were generated by higher degrees(10%~30%) of partial melting.The parental magmas of the Wudangshan Group and Yaolinghe Group basic lavas from Wudangshan area were then subjected to shallow level gabbroic(cpx + plag ± ol) fractionation and the chemical evolution of the basic lavas and basic dykes from other areas was controlled by a clinopyroxene(cpx) ± olivine(ol) fractionation.
【Fund】: 中国地质调查局综合研究项目(1212010611804)
【CateGory Index】: P581
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