Geochemical characteristics and its geological significance of the Late Paleozoic siliceous rocks in Qinfang Trough,southeastern Guangxi
Hu Lisha1, Xu Yajun1, Du Yuansheng1, Huang Hongwei2, Xu Wangchun1, Kuang Guodun2
1 State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences(Wuhan),Wuhan 430074,Hubei 2 General Academy of Geological Survey of Guangxi,Nanning 530023,Guangxi
Abstract：The Late Paleozoic siliceous rocks in the Qingfang Trough were well developed.Based on the analyses of major elements,trace elements and rare earth elements,it was concluded that the Late Paleozoic siliceous rocks contain high content of SiO2 and high silicification degree;the Upper Devonian Frasnian and Lower Carboniferous siliceous rocks have lower Al/(Al+Fe+Mn)value (0.14-0.24;0.07～0.81)and higher U/Th value(0.34～5.09;0.16～10.1),whereas the Famennian and Lower-Middle Permian siliceous rocks have higher Al/(Al+Fe+Mn)value(0.4～0.95) and lower U/Th value(0.1～2.1),illustrating that the Frasnian and the Lower Carboniferous siliceous rocks were influenced by the hydrothermal process but the Famennian and the Lower-Middle Permian siliceous rocks were biogenic origin;Ce/Ce*, LaN/YbN,and LaN/CeN values for the Upper Devonian siliceous rocks are 0.78～1.08,0.4～1.52 and 0.88～1.35,whereas these values for the Lower Carboniferous siliceous rocks are 0.55～0.91,0.12～1.8 and 1.12～1.79,and the Lower-Middle Permian siliceous rocks have Ce/Ce*,LaN/YbN,and LaN/CeN values of 1.01～1.62,0.72～2.71 and 0.62～1.9;Geochemical characteristics of the Late Paleozoic siliceous rocks in the Qinfang Trough indicated that the Qinfang Trough expanded within an epicontinental sea environment during the Late Devonian with hydrothermal activity,then expanded again in the Early Carboniferous with siliceous rocks formed in deep sea basin environment,and in the Early Permian the Qinfang Trough shrinked gradually to a continental margin basin. In a conclusion,the Qinfang Trough is more like a sea basin and may be belong to the Aulacogen of Paleo-Tethys Ocean in Late Paleozoic,and an ocean crust had never been formed.
Hu Lisha,Xu Yajun,Du Yuansheng et al. Geochemical characteristics and its geological significance of the Late Paleozoic siliceous rocks in Qinfang Trough,southeastern Guangxi[J]. JOPC, 2014, 16(1): 77-88.
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