粤中从化地区佛冈岩基白垩纪花岗岩LA-ICP-MS锆石U-Pb年代学及地球化学特征

LA-ICP-MS Zircon U-Pb Chronology and Geochemistry of Cretaceous Granites from Fogang Batholith in the Conghua Area,Central Guangdong Province

LA-ICP-MS锆石U-Pb定年结果表明,粤中从化地区发育一套白垩纪花岗岩,其形成时代为~145 Ma,属佛冈岩基的一部分。地球化学研究表明,花岗岩的SiO2含量为71.9%~77.72%(平均74.89%),Al2O3含量为12.17%~14.42%(平均13.24%),A/CNK为1.31~1.49(平均1.4),ALK全碱指数7.92~9.15(平均8.5),为过铝质高钾钙碱性系列花岗岩。它们的稀土元素总量(ΣREE)为(128.8~393.8)×10^(-6),Eu具负异常,δEu值为0.1~0.4,LREE/HREEE值为2.2~13.3;具有富集Rb、U、La、Nd、Sm和Lu,强列亏损Ba、Nb、Sr、P和Ti等元素特点。元素地球化学特征显示其为高分异I型花岗岩,可能是在高温条件下幔源物质诱导下地壳部分熔融后引发古老地壳杂砂-泥质源岩部分熔融而形成。综合区域地质资料分析,从化地区白垩纪花岗岩可能形成于古太平洋板块向欧亚板块俯冲的陆缘弧构造环境。

The LA-ICP-MS zircon U-Pb dating determined a~145 Ma Cretaceous granites in the Jurassic Fogang batholith of the Conghua area,Central Guangdong Province.The geochemical research of the granite shows that its SiO2 content is 71.9%~77.72%(average value is 74.89%),Al2O3 content is 12.17%-14.42%(av-erage 13.24%),A/CNK is 1.31~1.49(average value is 1.4),ALK(The total alkali index)is 7.92~9.15(average value is 8.5),which indicates it’s a peraluminous high-potassium calc-alkaline series granite.Their total rare earth elements(ΣREE)range from 128.8 to 393.8 ppm,with negative Eu anomaly,δEu value from 0.1 to 0.4,and LREE/HREEE value from 2.2 to 13.3.It is enriched in Rb,U,La,Nd,Sm and Lu,and strongly depleted in Ba,Nb,Sr,P and Ti.Elemental geochemistry shows that it belongs to a highly differentiated I-type granite,and might be formed by partial melting of ancient crustal sand-argillaceous source rocks caused by mantle-de-rived magma at high temperature.Combined with the regional geological data,the Cretaceous granite in the Conghua area may be formed under the continental margin arc tectonic background of the subduction of the ancient Pacific plate to the Eurasian plate.