粤北大宝山矿区花岗闪长斑岩LA-ICP-MS锆石U-Pb年龄及其地质意义

对粤北大宝山钼钨多金属矿区的花岗闪长斑岩进行了锆石阴极发光显微结构观察和LA-ICP-MS锆石微区U-Pb定年.在锆石阴极发光图像中, 两个花岗闪长斑岩样品中的锆石颗粒具有明显的振荡环带, 为典型的岩浆锆石.LA-ICP-MS U-Pb定年结果显示: 大宝山花岗闪长斑岩样品中具岩浆环带锆石区域12个分析点的206Pb/238U加权平均年龄为175.8±1.5 Ma(MSWD=0.037), 船肚花岗闪长斑岩样品中具岩浆环带锆石区域16个分析点的206Pb/238U加权平均年龄为175.0±1.7 Ma(MSWD=0.41).它们的形成时代约175 Ma, 为燕山早期第Ⅰ阶段(180~170 Ma)产物.本次对大宝山矿区花岗闪长斑岩形成时代的准确厘定, 为大宝山和船肚花岗闪长斑岩原本连为一体被后期构造错断的认识提供了新证据, 岩体错断部位是矿区Mo-W矿进一步勘探的重要方向.结合相关研究表明, 其成岩成矿动力学背景与邻区岩体相似, 为南岭地区同一期岩石圈伸展-减薄事件的产物.同时启示我们, 在南岭地区还存在燕山早期第一阶段(180~170 Ma)利于形成Mo-W矿的花岗岩类小岩体未被揭露. 

Geochronology and Its Geological Implications of LA-ICP-MS Zircon U-Pb Dating of Granodiorite Porphyries in Dabaoshan Polymetallic Ore Deposit,North Guangdong Province

The dating of LA-ICP-MS zircon U-Pb was carried out for granodiorite porphyries at Dabaoshan polymetallic ore deposit in North Guangdong Province. In cathodoluminescence (CL) image, most zircons in two granodiorite porphyry samples exhibit oscillatory zoning, which is typical for magmatic zircon. The dating of LA-ICP-MS zircon U-Pb of two samples shows the results that 12 points of oscillatory zoned domains of Dabaoshan granodiorite porphyry sample yields a group of weighted mean 206Pb/238U ages at (175.8±1.5)Ma (MSWD=0.037) and 16 points of oscillatory zoned domains of Chuandu granodiorite porphyry yields a group of weighted mean 206Pb/238U ages at (175.0±1.7) Ma (MSWD=0.41). So the epoch of granodiorite porphyry emplacement is nearly 175 Ma, belonging to the first stage of the early Yanshanian (180-170 Ma). According to the precise ages we have obtained, Dabaoshan and Chuandu granodiorite porphyries are a whole magamtic rock divided by the post-mineralization fault, and the faulted space is the most important direction for further exploration of Mo-W. The study, together with others, suggests that its geodynamic setting was the same as that of the near magamatic rocks, which formed in the same episode lithosphere extension event in Nanling region. In addition, we conclude that in the first stage of the early Yanshanian, some granodiorite porphyries favorable to forming Mo-W deposits have been undiscovered in Nanling region.