浙江莫干山花岗岩体锆石U-Pb、全岩Rb-Sr年代学、Sr-Nd-O同位素地球化学及成因研究

莫干山花岗岩体位于东天目山晚中生代火山盆地东端,用LA-ICPMS进行锆石U-Pb定年得到年龄为128.1±2.1Ma,全岩Rb Sr等时线定年结果为135.4±4.3 Ma,表明其属燕山晚期岩浆活动产物.莫干山花岗岩的Sr-Nd-O同位素分析结果为:初始87Sr/86Sr=0.70933;εNd(t)=-3.75～ - 6.4;δ18O=8.86‰～10.78‰,表明其成因类型属Ⅰ型花岗岩,是壳-幔物质混合形成的.按Sr Nd双变量二元混合模型计算得出源区物质中地壳端员和亏损地幔端员的贡献份额分别为47％～49％、51％～53％.莫干山花岗岩与建德群黄尖组火山岩的锆石U-Pb年龄、全岩Rb Sr等时线年龄基本一致,其Nd-Sr同位素组成也很相似,表明它们来自同一岩浆源.

Zircon U-Pb and Whole-rock Rb-Sr Chronology,Sr-Nd-O Isotopes and Petrogenesis of the Mogaoshan Granite Pluton in the Zhejiang Province

The Moganshan granite pluton locates in the eastern part of a late Mesozoic volcanic basin in the Tianmu mountain.LA-ICPMS U-Pb dating of zircon from the granite yields an age of 128.1±2.1Ma,and an isochron age of 135.4±4.3Ma is obtained from whole-rock Rb-Sr in the pluton,indicating it was formed in the late Yanshanian period.Results of Sr-Nd-O isotope analyses for the Moganshan granite(initial 87 Sr/86 Sr=0.70933;ε Nd(t) =-3.75—-6.4;δ 18 O=8.86‰—10.78‰) show that it belongs to I-type granite with a source of mixed mantle-derived rocks and crustal rocks.Calculations based on the bivariate(Sr-Nd) and two-components(mantle-and crust-rocks) mixing model suggest that contributions of depleted mantle end-member and crustal end-member in the formation of the granite are 47%—49%and 51%—53%,respectively.The zircon U-Pb age and the whole rock Rb-Sr age for the Moganshan granite are consistent with those of volcanic rocks in the Huangjie formation.Furthermore the Sr-Nd isotopic compositions of the granitic and volcanic rocks are also similar.Therefore,we conclude that the Moganshan granite and the volcanic rocks of the Huangjie Formation were derived from a same magmatic source.