吉林福安堡棒子山花岗岩锆石U-Pb年龄、岩石地球化学特征及其地质意义

Zircon U-Pb ages and petrochemical characteristics of Bangzishan granite in Fu'anpu of Jilin and their geological significance

棒子山岩体为福安堡钼矿床的赋矿围岩,其岩性主要为似斑状黑云母二长花岗岩、二长花岗岩、黑云母花岗闪长岩和花岗斑岩等。本次测得似斑状黑云母二长花岗岩和花岗斑岩的LA-ICP-MS锆石U-Pb年龄分别为179±2Ma、172±1Ma,形成于中侏罗世,属燕山早期。棒子山花岗岩的SiO2含量为61.89%～71.06%,相对较高;Al2O3含量很高,为14.54%～17.11%;K2O含量为2.28%～4.38%,Na2O含量为3.74%～7.82%,Fe2O3含量为2.34%～5.91%,MgO含量为0.55%～2.37%。微量元素特征显示,棒子山花岗岩富集Rb、K等大离子亲石元素和不相容元素U、Th,强烈亏损Ba、Ta、Nb、P、Ti等元素;稀土元素特征显示轻稀土富集,重稀土亏损,轻重稀土分馏明显,有轻微的Eu负异常。上述结果表明,棒子山花岗岩石为准铝质-弱过铝质高钾钙碱性系列I型花岗岩,其形成可能与太平洋板块的俯冲有关。

Bangzishan granitic pluton is the ore-hosting rock of Fu＇anpu molybdenum deposit,composed of porphyroid biotite monzonitic granites,monzonitic granites,biotite granodiorite and granite porphyry.The LA-ICP -MS zircon U-Pb dating of porphyroid biotite monzonitic granite and granite porphyry were 179 ±2 Ma and 172 ± 1 Ma,respectively,which corresponds to Middle Jurassic,belonging to Early Yanshanian in tectonic periods.The SiO2 content of Bangzishan granites was 61.89％ to 71.06％,Al2O3 was 14.54％ to 7.11％,K2O was 2.28％ to4.38％,Na2O was 3.74％ to 7.82％,Fe2O3 was 2.34％ to 5.91％,MgO was 0.55％ to 2.37％.The granites were strongly enriched in large ion lithophile elements （Rb and K） and incompatible elements （U and Th）,with depletion in Ba,Ta,Nb,P and Ti.The REE patterns demonstrated LREE enrichment and HREE deplition,with weak negative Eu anomalies.These results indicated that the Bangzishan granite was the metaluminous-weakly peraluminous Ⅰ-type granites of hight-K cale-alkaline serise in category,and it was the product of the subduction of the Paleo-Pacific plate.