秦岭造山带蟒岭花岗岩锆石LA ICP MS U Pb年龄及其地质意义

蟒岭花岗岩位于东秦岭地区商南—丹凤断裂带北侧的北秦岭构造带上,呈北西西走向,与区域构造线方向基本一致。本文报道了该岩体的锆石LA-ICP-MS U-Pb定年数据和地球化学数据,并结合前人的资料初步总结了该岩体的年代学特征。结果显示,蟒岭花岗岩的岩浆演化可以分为两个阶段:晚侏罗世—早白垩世的二长花岗岩(158.4±1.8Ma～160.5±1.3Ma)和早白垩世中期的钾长花岗岩(124.1±2.0Ma)。此外,样品09CL264获得锆石继承核部年龄为1883±36Ma、1860±35Ma,可能代表了源岩年龄。地球化学特征上,早期的二长花岗岩具有高硅、碱,K2O/Na2O>1,以及高Sr、低Yb、Y的特征,而晚期的钾长花岗岩具有高硅、碱,K2O/Na2O<1,低Sr、低Y、Yb的特征。其中,晚侏罗世—早白垩世的二长花岗岩(09CL260)的εHf(t)值变化于-9.4～-3.1,暗示其可能具有多源特征,源岩主要为下地壳元古宙物质。

LA ICP MS Zircon U Pb Ages and Implications for Tectonic Setting of the Mangling Granitoid Plutons in Qinling Orogen Belt

The Mangling granite is located on the north side of the Shannan—Danfeng foult,eastern sector of the north Qinling Orogen.The granite is in North—West—West strech and in agreement with structural lineament.The paper reports the results of Zircon LA-ICP-MS U-Pb age and geochemical data.The results show that the Mangling granite includs two granite emplacements.Early Monzogranite whose ages ranging from 158.4±1.8Ma to 160.5±1.3 Ma belongs to Late Jurassic Early Cretaceous period and the late alkali granite has an age of 124.1±2.0 Ma belonging to Middle Cretaceous.In addition,sample 09CL264 give inherited core age of 1883±36Ma and 1860±35 Ma belonging to proterozoic and may represent its protolith age.In geochemistry,monzogranite with the characteristics of high SiO2,K2O+Na2O,K2O/Na2O>1 and high Sr low Yb,Y.The alkali granite has the characteristic of high SiO2,K2O+Na2O,K2O/Na2O<1 and low Sr low Yb,Y.The εHf(t) values are from-9.4 to-3.1 which is consistent with previous study on εNd(t).In conclusion,the Mangling granite has character of multi-source and the main is proterozoic material in lower crust.