湘东北三墩铜铅锌矿区花岗岩的岩石成因——锆石U-Pb测年、岩石地球化学和Hf同位素约束

    Petrogenesis of the granites in Sandun area-Constraints from petrochemistry, zircon U-Pb chronology and Hf Isotope

    • 摘要: 对湘东北三墩铜铅锌矿区花岗岩进行了系统的锆石U-Pb年代学、岩石地球化学和Hf同位素分析。LA-ICP-MS锆石U-Pb定年表明,三墩铜铅锌矿区花岗岩成岩年龄为131.9±1.1Ma。三墩铜铅锌矿区花岗岩为一套强过铝质钙碱性系列花岗岩,富集U、Ta、Pb,亏损Ba、Nb、Sr、Zr、Ti等元素,稀土元素配分模式为右倾配分模式,具有弱负Eu异常。Hf同位素分析表明,三墩铜铅锌矿区花岗岩燕山晚期锆石εHft)值为-5.9~-2.4,Hf同位素二阶段模式年龄为1558~1338Ma,表明其物质来源于中元古代古老地壳岩石部分熔融。749.5Ma继承锆石核的εHft)值为+4.8,Hf同位素二阶段模式年龄为1355Ma,暗示其物质来源有幔源物质加入。三墩铜铅锌矿区花岗岩可能是由于中下地壳的熔融岩浆形成后,混入少量幔源物质上侵形成的。

       

      Abstract: In this paper, the authors studied the petrogenesis and tectonic-significance of the granite from the Sandun Cu-Pb-Zn polymetallic deposit in northeastern Hu'nan Province by means of zircon U-Pb isotope chronology, whole rock geochemistry and Hf isotope. LA-ICP-MS zircon U-Pb dating yielded crystallization age of 131.9±1.1Ma for the Sandun granite. The Sandun granite is a peraluminous high-Al calc-alkaline intrusive granite. The rocks are characterized by high U, Ta, Pb and low Ba, Nb, Sr, Zr, Ti val-ues. The REE distribution patterns are strongly LREE enriched and HREE depleted, with weakly negative Eu anomalies. The Hf iso-tope analyses show that the εHf(t) values of the late Yanshanian granite zircons are between -5.9 and -2.4, and the two stage Hf model ages ranging from 1558Ma to 1338Ma, which indicates that its parental magma was derived from partial melting of rocks of Middle Proterozoic paleo-crust. Inherited zircon with an age of 749.5Ma has the εHf(t) of +4.8 and two stage Hf model age of 1355Ma, re-spectively, which indicates that its parental magma was mainly derived from the mantle. The Sandun granite probably resulted from the formation of the molten magma in the middle and lower crust and the formation of a small amount of mantle derived material.

       

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