山西吕梁地区狐偃山碱性杂岩体LA-ICP-MS锆石U-Pb年龄及其地质意义

LA-ICP-MS zircon U-Pb geochronology of the Huyanshan alkaline intrusive complex in the Lüliang Mountain of North China Craton and its geological significance

为获取狐偃山碱性岩浆活动的时限,对狐偃山碱性杂岩体早晚2期侵入体进行LA-ICP-MS锆石U-Pb测年。结果显示,早期侵入体二长岩的^(206)Pb/^(238)U年龄加权平均值为127±1Ma(MSWD=3.7),属于早白垩世早期;晚期侵入体正长岩的^(206)Pb/^(238)U年龄加权平均值为114±4Ma(MSWD=3.5),属于早白垩世晚期。二长岩岩浆活动对应于华北克拉通中部碱性岩浆活动的高峰期(约130Ma),正长岩则代表华北克拉通中部最后一期碱性岩浆活动的时间(约114Ma);华北中部碱性岩浆活动与东部发生的强烈岩浆活动的时间一致,对应于华北克拉通岩石圈减薄的峰期。捕获岩浆成因锆石2.5~2.4Ga的年龄,对应华北克拉通化的时期;2.2~2.1Ga的继承锆石年龄,代表华北在2.5Ga左右克拉通化之后于2.3~2.0Ga经历的一次陆内拉伸-裂谷-岩浆事件;约1.8Ga继承锆石的年龄,是华北克拉通发生在陆内裂谷背景下的大规模岩浆作用的表现;232~220Ma的继承锆石年龄,代表晚三叠世华北克拉通发生的一期岩浆-构造热事件的时间。

In order to constrain the age of alkaline magmatism, the authors determined U-Pb zircon ages by the high accuracy LAICP-MS method for the early and late stage of Huyanshan alkaline intursive complex. Zircons from monzonite yielded a weighted mean^(206)Pb/^(238)U age of 127±1Ma, indicating that the monzonite occurred at the early stage of the Early Cretaceous, corresponding to the peak time of alkaline magmatism in central North China Craton. Zircons from syenite have a weighted mean^(206)Pb/^(238)U age of114±4 Ma, suggesting that the syenite was formed at the late stage of the Early Cretaceous, representing the last alkaline magma activity in central North China Craton. The time of alkaline magmatism was consistent with the magmatism in east of North China Craton, which was the peak period of lithospheric thinning of North China Craton. In addition, the inherited zircons have ages of 2.5~2.4Ga and 2.2~2.1Ga, respectively, corresponding to the cratonization stage of North China Craton and the intracontinental extension-rifting event in 2.3~2.0Ga. The age of ~1.8Ga for inherited zircons resulted from intracontinental rifting and mass magmatism in the North China Craton. The ages of 232~220Ma were given by inherited zircons, representing magmatic-tectothermal event of North China Craton in Late Triassic.