广西浦北五皇山国家地质公园花岗岩地球化学特征及其成因分析

Geochemical Characteristics And Genetic Aoalysis Of Granite In Wuhuangshan National Geopark In Pubei,Guangxi

2015年广西浦北五皇山因其奇特的花岗岩景观获批国家地质公园,五皇山所属的浦北岩体是大容山-十万大山花岗岩带的一部分,其花岗岩的成因尚未达成共识。以野外地质调查和室内岩石薄片鉴定为基础,结合主量元素、微量元素、Sr同位素等地球化学分析得出:五皇山花岗岩属于强过铝质高钾钙碱性系列-钙碱系列(A/CNK=1.214~1.543);明显相对富集轻稀土元素(LREE)(143.7×10-6~184.23×10-6),相对亏损重稀土元素(HREE)(11.72×10-6~12.73×10-6),LREE/HREE介于10.87~12.73之间;Eu负异常明显(δEu=0.49~0.80),稀土元素球粒陨石标准化配分曲线为轻稀土元素富集的右倾型;相对富集大离子亲石元素Rb、Th、U,相对亏损高场强元素Ta、Nb和Ba、Sr。通过本文工作,并结合前人关于五皇山花岗岩的分析资料,认为五皇山花岗岩属于S型壳源花岗岩,且在其形成过程中经历了高分异演化作用。

Wuhuangshan in Pubei,Guangxi,was granted the national Geological Park in 2015 due to its peculiar granite landscape.Wuhuangshan belongs to Pubei pluton,which is part of the Darongshan-Shiwandashan granitoid belt,and there is no consensus on its granite origin.Based on field geological survey and indoor rock thin section analysis,combined with geochemical analysis of major elements,trace elements,Sr isotopes,etc.,it can be concluded that Wuhuangshan granite belongs to strong peraluminized high-potassium calc-alkali series-calc-alkali series(A/CNK=1.214~1.543);The content of light rare earth elements(LREE)is between 143.7×10-6~184.23×10-6,the content of heavy rare earth elements(HREE)is between 11.72×10-6~12.73×10-6,and the content of LREE/HREE is between 10.87~12.73,showing obvious characteristics of relatively rich LREE and relative deficit of HREE;They show negative Eu anomalies withδEu ratios being 0.49~0.80,the chondrite-normalized REE patterns show right declining,exhibiting enrichment of LREE;They are enriched in Rb,Th and U,and depleted in Ta,Nb,Ba and Sr.Through the work of this paper,combined with the previous analysis data of Wuhuangshan granite,the authors hold that Wuhuangshan granite is S-type crust-source granite and has experienced the high differentiation and evolution during its diagenesis.