秦岭造山带蟒岭花岗岩锆石LA-ICP-MSU-Pb年龄及其地质意义

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

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。

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 streeh 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 proterozoie 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 ε_Hf（t） values are from -9.4 to -3.1 which is consistent with previous study on ε_Nd （t）. In conclusion, the Mangling granite has character of multi-source and the main is proterozoic material in lower crust.