湘东邓阜仙二云母花岗岩锆石U-Pb年代学及地球化学研究

Zircon U-Pb Geochronology and Geochemistry Characteristics of Dengfuxian Two-mica Granite, Eastern Hunan Province, China

邓阜仙花岗岩体位于湖南茶陵县东北部,是一个由黑云母花岗岩、二云母花岗岩和白云母花岗岩组成的复式岩体。其中,二云母花岗岩与钨成矿关系最为密切。锆石LA-ICP-MS U-Pb同位素定年测得二云母花岗岩的加权平均年龄为154.4±2.2 Ma(MSWD=5.6,n=20),为燕山早期侵位。岩石地球化学研究表明,邓阜仙二云母花岗岩具有高硅、富碱、贫镁铁、强过铝质和高分异的特点。花岗岩相对富集大离子亲石元素Cs、Rb、K和高场强元素Th、U、Pb,亏损Ba、Sr和Ti等,稀土总量偏低(ΣREE平均值为90.59×10-6),轻稀土相对富集(LREE/HREE比值平均为9.97),铕负异常显著(δEu平均值为0.34),稀土元素配分模式呈右倾型。根据区域地质和花岗岩地球化学特征,确定岩石为S型花岗岩,形成于造山后伸展构造环境。

The Dengfuxian granitic body located in the northeast Chaling,Hunan province,China,is composed of biotite granite,two-mica granite and muscovite granite.Among them,two-mica granite has closely related with tungsten mineralization.The zircon LA-ICP-MS U-Pb weighted average age of 154.4±2.2 Ma（MSWD=5.6,n=20） indicates that the intrusion of two-mica granite occurred at Early Yanshanian.Dengfuxian two-mica granite is strongly peraluminous,with high Si and alkali contents and low Mg and Fe contents,showing geochemical characteristics of high differentiation.Two-mica granite is rich in large ion lithophile elements（Cs,Rb and K） and high field strength elements（Th,U and Pb）,but deplete in Ba,Sr and Ti.These two-mica granitic rocks have low ΣREE content（average ΣREE=90.59×10-6）,pronounced negative Eu anomaly（average δEu=0.34） and LREE enrichment（average LREE/HREE=9.97）.The chondrite-normalized REE distribution pattern is right-inclining type.Combining the regional geology with bulk rock geochemistry,Dengfuxian two-mica granite is believed to be S-type granite and formed in an extensional tectonic setting during Early Yanshanian.