宁芜盆地凹山铁矿床辉长闪长玢岩和花岗闪长斑岩的锆石U-Pb年龄及其地质意义

摘要

宁芜盆地是长江中下游多金属成矿带的重要矿集区之一,是玢岩型铁矿成矿模式建模的基地.玢岩型铁矿床成矿时代的约束对区域成岩成矿作用及成矿动力学背景研究具有重要的意义.凹山铁矿床是宁芜盆地玢岩型铁矿床的典型代表之一,本文选择矿区发育的两种与成矿作用关系密切的岩浆岩为研究对象,进行锆石LA-MC-ICP-MS U-Pb年代学研究,获得赋矿辉长闪长玢岩成岩年龄为131.7±0.7Ma,后期穿切矿体的花岗闪长斑岩成岩年龄为126.1±0.5Ma.凹山铁矿床成矿年龄在131.7～126.1Ma之间,属于早白垩纪.成矿作用伴随盆地早期岩浆作用而形成,受区域岩石圈伸展和减薄作用的制约.%Ningwu basin is one of the important ore districts in the Middle-Lower Reaches of the Yangtze River Belt, China, and also a base for constructing the metallogenic model of porphyry-type iron deposits. Constraint of metallogenic time of porphyry-type iron deposits to regional diagenesis and mineralization and metallogenic dynamic settings is of extremely important significance. Aoshan iron deposit is one of the representive porphyry-type iron deposits in Ningwu basin. Two types of magmatic rocks closely related to mineralization were selected as our study objects. Detailed zircon U-Pb age dating for magmatic rock samples yields an age of 131. 7±0. 7 Ma for gabbrodiorite porphyrite and 126. L±0. 5Ma for granodiorite porphyry cutting across the main orebodies using LA-MC-ICP-MS. According to the relationship between petrogenesis and mineralization, the age of mineralization of Washan iron deposit is 131. 7 - 126. 1Ma, suggesting that it belongs to the Early Cretaceous. The mineralization associated with early magmatism in Ningwu basin occurred in an extensional tectonic regime, possibly induced by lithospheric thinning.