浙江安吉多金属矿区坞山关杂岩体锆石LA-ICP-MS U-Pb年龄、地球化学特征及地质意义

LA-ICP-MS U-Pb Ages,Geochemical Characteristics of the Zircons from Wushanguan Complex Body in Anji Mining Area,Northwestern Zhejiang and Their Geological Significances

安吉港口多金属矿床在成因上与坞山关杂岩体密切相关,该杂岩体包括黑云母二长花岗岩、钾长花岗岩、花岗闪长岩和细粒花岗岩。本文采用岩相学、CL和LA-ICP-MS等方法对前三套岩石单元中的锆石进行了成因矿物学、微区微量元素和U-Pb年代学特征等相关研究。年代学结果显示,杂岩体大致形成于晚侏罗世—早白垩世,按前述排列顺序,三岩石单元成岩年龄分别为141.0±1.4Ma(n=13,MSWD=1.3),138.1±1.0Ma(n=14,MSWD=0.92)和137.0±1.8Ma(n=13,MSWD=1.9)。研究过程中发现的年龄为518±9Ma和624±9Ma的继承锆石,暗示杂岩体成岩过程中有晋宁晚期和加里东早期古老地壳物质的熔融或同化混染。锆石Ti温度记显示,杂岩体中黑云母二长花岗岩、花岗闪长岩锆石结晶温度基本一致,均值分别为657℃和653℃,钾长花岗岩锆石结晶温度略高,均值为698℃。区域构造环境、岩体被动侵位、构造张性和张剪性特征表明,矿区在约141～137Ma前后已处于拉张—伸展构造背景之下,杂岩体及其相关成矿作用受该环境控制。本次研究及野外调研结果表明,杂岩体与矿区多金属矿床具有密切的时空关系。浙江淳安铜山锡矿、安吉多金属矿床成岩成矿数据表明,钦—杭成矿带东段在晚侏罗世—白垩世约148～134Ma还存在一期成岩成矿作用。

As the major granite intrusion in Anji mining area,Wushanguan complex body is composed by four rock units of biotite-monzonitic granite,granodiorite,moyite and fine-grained granite.Zircons from the first three units are analyzed by petrography,cathodoluminescence （CL） and LA-ICP-MS,and the results show that the complex body formed in Late Jurassic and Early Cretaceous,and biotite-monzonitic granite,granodiorite and moyite formed in 141.0±1.4Ma （n=13,MSWD=1.3） ,138.1±1.0Ma （n=14,MSWD=0.92） and 137.0±1.8Ma （n =13,MSWD=1.9） respectively.That two inherence zircons have been found,whose U-Pb ages are 518±9Ma and 624±9Ma respectively,suggests some old crustal materials of Early Caledonian and Late Jinningian were carried in magma by partial melting and （or） assimilation-contamination in the forming process of Wushanguancomplex body.The crystallization temperature of zircons in biotite-monzonitic granite,granodiorite and moyite are ranging from 628～747℃ （with an average of 657℃ ） ,625～715℃ （with an average of 653℃ ） and 618～765℃ （with an average of 698℃） respectively.The passive emplacement of the complex body,tensional and tenso-shear character of NW faults and regional tectonic setting indicate that Anji mining area had been under the extensional environment from 141 to 137Ma,and the diagenesis and mineralization events associated with the complex body are controlled by this setting.Analysis results and some evidences from geological investigation indicate in Anji mining area the polymetallic mineralization and the complex body have a close association in time and space.Anji polymetallic deposit （about 141～134Ma） and Tongshan Sn deposit （about 147～143Ma） in Zhejiang province indicate that anther magmatic-mineralizing event had occurred during Late Jurassic-Early Cretaceous （about 148～134Ma） in East Qinzhou-Hangzhou metallogenic belts.