安徽宁国刘村二长花岗岩地球化学特征、LA-ICP-MS锆石U-Pb年龄及其地质意义

Geochemical Characteristics and LA-ICP-MS Zircon U-Pb Geochronology of the Liucun Monzogranite in Ningguo,Anhui Province and Their Geological Significance

刘村岩体位于浙江安吉和安徽广德两县交界处的皖南地区,该岩体主要为浅红略带肉红色中细—粗中粒似斑状二长花岗岩,岩体沿由寒武系地层组成的背斜轴部侵入。刘村二长花岗岩为具高钾、富碱、Mg#小等特征的准铝质-过铝质A型花岗岩。稀土元素的球粒陨石标准化曲线右倾斜明显、铕谷较深。微量元素原始地幔标准化蛛网图见明显的Ti、Sr谷,曲线整体右倾,岩体整体亏损HFSE,富集LILE。主、微量元素的地球化学特征研究均表明,形成刘村二长花岗岩的岩浆源于岩石圈地幔,并受到地壳物质的混染,岩体岩浆演化过程中发生有磷灰石、角闪石、辉石、榍石等矿物的结晶分异作用。通过LA-ICP-MS锆石U-Pb法确定刘村二长花岗岩年龄为132.84±0.57Ma,表明该岩体形成于早白垩世,为皖南地区燕山期第二期岩浆活动的产物。刘村二长花岗岩形成于晚侏罗世—早白垩世中国东部构造活化和构造机制由挤压开始向拉张转折的转换阶段。该区金化探异常明显,是寻找金、银、钨(钼)多金属矿的有利地段。

The Liucun intrusion is located in the southern part of Anhui Province where is the junction between Anji County in Zhejiang and Guangde County in Anhui.The intrusion consists of pink to pinkish red finecoarse grained porphyritic monzogranite.The intrusion invades into the anticlinal axis composed of Cambrian strata.The Liucun monzogranite is the para-aluminous to peraluminous A-type granite with the features of high-potassium,alkali-rich and low-Mg#.The rare earth element chondrite-normalized distribution pattern shows distinct right leaning and big Eu anomaly.The spider diagram of the primitive mantle-normalized trace element curves have obviously negative Ti and Sr anomalies and right leaning. Overall,the intrusion has low HFSE and high LILE.Geochemical characteristics of major and trace elements indicate that the magma formed the Liucun monzogranite came from lithospheric mantle and contaminated by the continent crust.The process of magmatic evolution had experienced crystallization and differentiation of the minerals such as apatite,hornblende,pyroxene,titanite and so on.LA-ICP-MS zircon U-Pb dating yielded an age of 132.84±0.57 Ma for the Liucun monzogranite,suggesting that it belongs to early Cretaceous and should be the product of second stage magmatic activity of the Yanshanian in southern Anhui province.The Liucun monzogranite formed from the late Jurassic to early Cretaceous structure activation and tectonic mechanism converting from compression to extension.This area is a favorable place for prospecting gold,silver,tungsten-molybdenum polymetallic deposits because of its obvious geochemical gold anomalies.