| North-northeast Guangxi belongs to the western part of Nanling Mountains.Geotectonic location is in the western part of the Yangtze-Cathaysian block junction zone,which is also the intersection of the Jiangnan orogenic belt and the South China fold belt.Granites are widely exposed in the area,However,there are few systematic comparative studies on geochemical characteristics.Therefore,the formation period covers four different magmatic active periods: Jinning,Caledonian,Indosinian and Yanshanian.It is an ideal place for comprehensive study of granites.In this paper,several granite bodies in the area,such as Motianling,Yuechengling,Haiyangshan and Huashan,are selected as the research objects.Based on the geochemical characteristics of major elements,trace elements and hydrocarbon components,and combined with previous studies,the geological background,geochemistry and regional tectonics of several granite bodies in the area are comprehensively compared.The petrogenetic types and tectonic setting of granites in North-Northeast Guangxi are discussed.The main achievements and understandings are as follows:(1)The granites in North-Northeast Guangxi are characterized by enriching silicon,alkali,iron,lacking calcium and magnesium.Most of the rocks belong to peraluminous and high potassium calc-alkaline acid granites.(2)The granites in North-Northeast Guangxi have the characteristics of enriching trace elements like W,Sn,Bi and Pb,as well as W-Sn element assemblage,which reflects that W,Sn and other elements are generally enriched in the rocks of this area,which is consistent with the characteristics of many W-Sn polymetallic deposits(spots)found in this area.(3)According to the REE characteristics of granites in North-Northeast Guangxi,the ?REE varies widely.?REE and LREE/HREE show a certain incremental relationship from Jinning period(Motianling,Yuanbaoshan)to Caledonian period(Maoershan,Yuechengling,Haiyanshan)to Yanshanian period(Dupangling,Huashan and Guposhan),reflecting there are some differences in source rock characteristics and tectonic environments of epoch granites in different geological times.On the whole,Eu negative anomaly is obvious,LREE beneficiation,HREE depleted,light and heavy rare earth fractionation is good,which indicates that magma differentiation is more thorough.On the whole,Eu negative anomaly is obvious,light rare earth is enriched,heavy rare earth is lacking,light and heavy rare earth fractionation is good,which indicates that magma differentiation is more thorough.(4)The hydrocarbon gas components in granites in North-Northeast Guangxi are much higher than the background values,it shows that hydrocarbon components are involved in the process of diagenesis and mineralization in research area.The distribution ratios of hydrocarbon gas components are obviously different,indicating that in the process of magma intrusion,differentiation evolution and diagenesis,with the change of environmental temperature,pressure,oxygen fugacity,acidity and alkalinity,the hydrocarbon components in granite also show regular changes in macro and micro characteristics.It confirms that the geochemical characteristics of hydrocarbon components have an indicative effect on the material migration and environmental changes during the formation and evolution of granite.(5)After a comprehensive discussion and comparative analysis of the geological background,geochemical characteristics and regional tectonic environment of the four granites formed in different geological periods in northern,northeastern and Eastern Guangxi,it is found that most of the Jinning and Caledonian granites in North-Northeast Guangxi have typical S-type characteristics,mostly formed by remelting of the upper crust,and most of their source rocks are formed by extrusion.In compressive environments,most Yanshanian granites have the characteristics of A-type granites,mostly formed by crust-mantle mixtures,and most of their source rocks are formed in relatively extensional tectonic environments. |
PDF Full Text Request