粤西北太保花岗岩体LA-ICP-MS锆石U-Pb年代学研究

LA-ICP-MS U- Pb zircon geochronology of Taibao granite in northwestern Guangdong

粤西北太保花岗岩体位于南岭花岗岩带西段,出露的岩石较复杂,主要岩性有角闪石黑云母二长花岗岩、角闪石黑云母花岗闪长岩和石英二长闪长岩。前人在20世纪60年代采用黑云母K-Ar法测得该岩体年龄为370 Ma,其后相关研究资料也一直视其为加里东期花岗岩。本文在野外地质调查和岩相学研究的基础上,利用LA-ICP-MS锆石U-Pb定年法对太保花岗岩体进行了系统的年代学研究。结果显示,组成太保花岗岩体主体的角闪石黑云母二长花岗岩及其中的闪长质包体形成年龄分别为158.4±2.0 Ma和160.5±1.6 Ma,两者年龄在误差范围内基本一致,应为同期形成;角闪石黑云母花岗闪长岩和石英二长闪长岩的年龄分别为151.5±1.8 Ma和157.6±1.5 Ma。结果表明太保花岗岩体形成于晚侏罗世,为燕山期花岗岩。

Taibao granitic pluton is located in western Nanling granite belt and consists of hornblende-biotite monzonitic granite,hornblende-biotite granodiorite,and quartz monzodiorite. A biotite K- Ar age of 370 Ma for the pluton was reported in 1960＇s and since then the pluton was considered to be Caledonian. On the basis of field investigation and petrographic observations,a systematic LA-ICP-MS U- Pb zircon geochronological study was recently performed on the pluton. The hornblende-biotite monzonitic granite which is the main body of the pluton and its dark dioritic enclaves yielded ages of 158. 4 ± 2. 0 Ma and 160. 5 ± 1. 6 Ma respectively. Both ages are within error,suggesting their possible relation to a common magmatic episode. The hornblende-biotite granodiorite and the quartz monzodiorite yielded ages of 151. 5 ± 1. 8 Ma and 157. 6 ± 1. 5 Ma respectively. The geochronological results demonstrate that the Taibao granitic pluton was emplaced in the Late Jurassic time during the Yanshanian orogeny.