满洲里达石莫盆地流纹岩、花岗斑岩SHRIMP锆石U-Pb年龄及其地质意义

Zircon SHRIMP U-Pb Ages and Its Geological Significance to the Rhyolite and Granite Porphyry in Dashimo Basin,Manzhouli

满洲里达石莫盆地火山岩系由下部的铁镁质火山岩组合、中部的高钾钙碱性流纹岩-碱性粗面岩组合和上部的铁镁质火山岩组合所构成,并有花岗斑岩侵入。SHRIMP锆石U-Pb年龄表明,流纹岩和花岗斑岩锆石的^206Pb/^238 U年龄分别为143.3±1.3Ma和143.0±1.8Ma,两者在误差范围内一致,同为早白垩世早期岩浆活动的产物。通过区域地层对比,结合已有的高精度锆石U-Pb年龄数据,可将达石莫盆地及大兴安岭北部原塔木兰沟组、原上库力组、原梅勒图组火山岩中的铁镁质火山岩组合（年龄大于145Ma的部分）归入塔木兰沟组,高钾钙碱性流纹岩-碱性粗面岩组合（年龄为145-130Ma的部分）归入上库力组,年龄小于127Ma的部分铁镁质火山岩组合归入梅勒图组。依照中国东部、俄罗斯东部和蒙古东部与火山岩有关的热液型铀矿主要赋存在早白垩世早期火山岩与次火山岩接触带附近的事实,推测达石莫盆地流纹岩与花岗斑岩的接触带是铀矿勘查值得关注的部位。

The lower and upper layer of volcanic series in Dashimo basin of southern Manzhouli is characterized by the combination of mafic volcanic rocks,and the middle is characterized by the combination of the high potassium calc-alkaline rhyolite-alkaline trachyte,accompanied by the intrusion of granitic porphyry.The zircon SHRIMP U-Pb dating results of rhyolite and granite porphyry show that rhyolite and granite porphyry are 143.3±1.3 Ma、143.0±1.8 Ma respectively,the rhyolite and granite porphyry belong to Early age of Early Cretaceous epoch,the isotopic age of rhyolite and granite porphyry consistent within the error range,they are the products of the same magmatic evolution.Based on the study of regional stratigraphic correlation,combined with the published high-precision U-Pb zircon age data,the volcanic rocks from former Tamulangou formation,former Shangkuli formation and the former Meiletu formation in Dashimo basin and the northern great Xingan range was devided into three parts.The part of mafic volcanic rocks with U-Pb age greater than 150 Ma was devided into Tamulangou formation,the part with less than 127 Ma devided into Meiletu formation and the part of high-K calc-alkaline rhyolitetrachyte assemblage with U-Pb age range from 145 Ma to 130 Ma was devided belong into Shangkuli formation.Besides,the research results of volcanic-related hydrothermal uranium deposit in Eastern China,Eastern Russia and Eastern Mongolia indicate that the contact interface of subvolcanic and volcanic rocks of early age of early Cretaceous provide favorable room for mineralization.From this viewpoint,the space nearby the contact interface of rhyolite and granite porphyry in Dashimo basin is a favorable space for hydrothermal uranium despoit.