赣中早白垩世橄榄玄粗岩(Shoshonite)系列火山岩的厘定及成因研究  

Identification and Genesis of the Early Cretaceous Shoshonitic Volcanic Rock Series in Central Jiangxi Province

作　　者：吴俊奇[1] 谭桂丽[2] 章邦桐[1] 凌洪飞[1] 陈培荣[1] 

机构地区：[1]南京大学地球科学与工程学院,内生金属矿床成矿机制研究国家重点实验室,南京210093 [2]南京地质矿产研究所,南京210016

出　　处：《高校地质学报》2011年第4期479-491,共13页Geological Journal of China Universities

基　　金：中国核工业地质局十一五科研项目(2006YG026)资助

摘　　要：对赣中地区打鼓顶组第四岩性段中基性火山岩的岩石-地球化学特征系统研究表明,这一岩性段的火山岩具有高碱、富钾、低钛、贫铁以及富集轻稀土和大离子亲石元素等特征,据此厘定其为橄榄玄粗岩-安粗岩组合,属典型的大陆板内橄榄玄粗岩系列火山岩。这套火山岩的全岩Rb-Sr等时年龄为(138±8.8)Ma,ISr偏高,中等的εNd(t),富放射性成因铅。盛源盆地及邻区橄榄玄粗岩系列火山岩的△7/4Pb值为14～19.6(平均值为16),△8/4Pb值为70.5～97(平均值为89.2),△Sr值为121.5～161.8(平均值为136.3),显示存在典型的Dupal同位素异常。根据Sr-Nd,Sr-Pb,Nd-Pb,Pb-Pb同位素相关性分析,判明赣中地区橄榄玄粗岩是由亏损地幔端元(DM)和岩石圈富集地幔端元(LEM)在源区混合形成的。按Nd,Sr双变量二元混合方程式计算,得出源区物质中亏损地幔端元(DM)和岩石圈富集地幔端元(LEM)所占份额分别为37%(平均值)和63%(平均值)。赣中地区早白垩世橄榄玄粗岩系火山岩的形成反映了华南板块内部在燕山晚期发生的一起重要的伸展构造事件。The forth unit of the Daguding Group in central Jiangxi Province consists of intermediate to basic volcanic rocks in the Shengyuan basin and adjacent areas. Our systematic study of petrology and geochemistry of this unit identifies that these rocks belong to typical interplate shoshonitic volcanic rock series,which are characterized by high contents of total alkali and K2O,low contents of TiO2 and iron,and an enrichment of the LREE and LILE elements. The Rb-Sr isochron age of the shoshonite series is（138±8.8） Ma,with distinctively high initial Sr isotopic ratios;intermediate initial Nd isotopic ratios and enriched radiogenic Pb. In addition,the shoshonite series shows a remarkable Dupal anomaly（7/4Pb=14～19.6 with an average value of 16;8/4Pb=70.5～97 with an average value of 89.2;Sr=121.5～161.8 with an average value of 136.3） . The correlations of Sr-Nd,Sr-Pb,Nd-Pb and Pb-Pb isotopes imply a mixing source of the depleted mantle（DM） endmember and the lithosphere enriched mantle（LEM） endmember. According to the two-component（Sr-Nd） mixing equation,the source of the shoshonite series is composed of about 37% DMendmenber and 63% LEM endmember. The existence of the early Cretaceous shoshonitic volcanic rock series in central Jiangxi Province suggests an important episode of extension in South China during the late Yanshanian period.

关 键 词：橄榄玄粗岩 岩石-地球化学特征 SR-ND-PB同位素 岩石圈富集地幔 赣中 

分 类 号：P642.252[天文地球—工程地质学]