川西松林口岩体锆石U-Pb定年及其地球化学特征

松林口岩体位于松潘—甘孜造山带中东部,为确定岩体的侵位时代和地球化学特征,通过镜下薄片观察、主微量元素分析以及锆石U-Pb测年,对松林口岩体进行了研究。结果表明,松林口岩体由二长花岗岩体和花岗闪长岩体组成,花岗闪长岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（212.4±0.9） Ma （MSWD=0.66）,二长花岗岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（222.4±1.1） Ma （MSWD=0.39）,形成于晚三叠世,由两期次岩浆作用形成;岩石的SiO₂含量56.56%~61.97%;铝饱和指数A/CNK=0.93~1.05,全碱含量3.78~5.38,K₂O/Na₂O=1.02~1.68,里特曼指数σ=1.194~1.612,样品属于准铝质中—高钾钙碱性岩系列。岩石轻重稀土比值LREE/HREE=5.22~7.13,La_N/Yb_N比值为6.93~8.96,轻、重稀土分异较明显,具较强的负Eu异常。岩石Mg^#值较高（50.97~61.27）,w（Rb）/w（Sr）为0.12~0.25,Rb-（Y+Nb）图解显示为后碰撞环境。因此,松林口二长花岗岩—花岗闪长岩属后碰撞准铝质中—高钾钙碱性I型花岗岩类。

ZIRCON U-PB DATING AND GEOCHEMICAL CHARACTERISTICS OF THE SONGLINKOU PLUTON, WESTERN SICHUAN

The songlinkou pluton is located in the mid-eastern Songpan-Ganzi orogenic belt. It was studied by microscopical observation, major and trace element analysis and zircon U-Pb dating, in order to determine the emplacement age and geochemical characteristics of the pluton. The results show that the Songlinkou pluton is composed of monzonitic granite and granodiorite which formed by two stages of magmatism in the late Triassic, the weighted mean age of zircon of granodiorite is 212.4±0.9 Ma (MSWD=0.66), and the weighted mean age of zircon of monzonitic granite is 222.4±1.1 Ma(MSWD=0.39). The pluton content of SiO₂ is 56.56%~61.97%, A/CNK value is 0.93~1.05, total alkali 3.78~5.38, K₂O/Na₂O 1.02~1.68, Rittmann index 1.194~1.612, so that the rocks belong to metaperaluminous mid-high K Calc-alkaline series. The LREE/HREE is 5.22~7.13, and La_N/Yb_N is 6.93~8.96, light and heavy rare earths are distinct, with obvious negative Eu anomalies. The rocks have high Mg# values(50.97~61.27), w(Rb)/w(Sr) is 0.12~0.25, and the Rb-(Y+Nb) diagram shows that it belongs to post-collision environment. Therefore, Songlinkou monzonitic granite-granodiorite belongs to post-collision metaperaluminous mid-high K Calc-alkaline I-type granite.