临汾断陷盆地孤峰山花岗闪长岩的地球化学和年代学及其地质意义

Geochemistry,Geochronology and Geological Significance of Gufengshan Granodiorite in Linfen Grabben Basin

临汾断陷盆地孤峰山花岗闪长岩的S iO2含量为64.62%~65.57%,具有富碱（Na2O＋K2O=7.38%~7.71%）、富钠（Na2O/K2O=1.37~1.54）、准铝质（A/CNK=0.94~0.99）和较低镁指数（Mg#=31.8~36.2）的特点,属于高钾钙碱性岩系。岩石明显富集轻稀土[（La/Yb）N=17.0~19.3],基本不显示Eu异常（δEu=0.94~1.04）,富集大离子亲石元素K、Rb、Ba、Sr等,Sr/Y比值高（Sr/Y=59.3~67.2）,亏损高场强元素Nb、Ta、Ti和Y。岩石学和地球化学特点表明该花岗闪长岩由加厚的基性下地壳部分熔融形成。对岩石进行的激光探针等离子体质谱（LA-ICP-MS）锆石U-Pb同位素年代测定获得了132.2±9.2M a的206Pb/238U加权平均年龄,该年龄与华北地块岩石圈减薄与破坏作用的峰期时间基本一致。部分锆石含有2590.9M a的内核,反映该地区在太古宙晚期发生过相应的构造事件。结合区域地质资料分析认为,孤峰山花岗闪长岩是华北地块早白垩世峰期伸展作用期间的产物,华北地块早白垩世期间的岩石圈减薄与破坏作用向西影响到了太行山以西的临汾断陷盆地一带。

The Gufengshan granodiorite makes up the Gufeng Mountain,is located in the Linfen grabben Basin,belongs to high-K calc-alkaline series,and SiO2 varying in the range of 64.62%~65.57%,has the features of high alkali（Na2O＋K2O=7.38%~7.71%）,high Na（Na2O/K2O=1.37~1.54）,A/CNK=0.94~0.99,which falls into the range of metaluminous rocks,and low magnesium index（Mg#=31.8~36.2）.The rock is riched in LREE [（La/Yb）N=17.0~19.3],with little Eu anomalies（δEu=0.94~1.04）,riched in LILE K,Rb,Ba,Sr et al.,high Sr/Y（Sr/Y=59.3~67.2） and flatter HFSE Nb,Ta,Ti,Y.Petrological and geochemical characteristics indicate the granodiorite results from the partial melting of thickening mafic lower crust.Zircons from these rocks are used in LA-ICP-MS U-Pb dating,yielding a weighted mean 206Pb/238U age of 132.2 9.2Ma,which is consistent with the peak time of the lithospheric thinning and the destruction of the North China Block.The core of some zircons with the age of 2590.9Ma shows that some corresponding tectonic events happened in Neoarchean.Based on the regional geological data analysis,the Gufengshan granodiorite is the product of the extension being coetaneous to the peak period of the lithospheric thinning and destruction of North China Block,and such lithospheric thinning and destruction happened in the Early Cretaceous in North China block affected westwards the Linfen grabben basin region on the west Taihang Mountains.