赣南吉埠黄沙岩体的锆石铀-铅年代学研究及其地质意义

摘要

赣南地区吉埠黄沙岩体的风化壳产出离子吸附型稀土矿床,但对其年代归属缺乏准确认识.利用从黄沙岩体风化壳中挑选出的锆石,开展了U-Pb法年代学研究.激光剥蚀-多接收器电感耦合等离子体质谱法(LA-MC-ICPMS)分析表明,岩体的“Pb/238U加权平均年龄为(242.5±1.8)Ma,说明吉埠黄沙岩体的成岩时代为印支期初期,而不是前任推断的燕山期.结合南岭区域发现的其他印支期岩体可知,印支运动在华南地区具有广泛影响,岩浆活动规模和出露面积较以往认识增大.纬度较高的黄沙岩体发生稀土矿化的事实进一步说明,1∶20万兴国幅、井冈山幅,乃至宁化幅内的印支期岩体也具有发生稀土矿化的条件,在今后的找矿工作中应给予重视.%Jibu Huangsha granitic intrusions in Southern Jiangxi province hosted several ion adsorption type rare earth element (REE) deposits, but its diagenic age is still unknown. In this paper, the U-Pb age of zircon separated from the weathering crust of Jibu Huangsha granitic intrusions was dated by using Laser Ablation-Multicolleetor Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICPMS). The dating results show that the weighted average 206Pb/238U age is (242.5 ±1.8) Ma, which indicates that the Jibu Huangsha intrusion formed in the early Indo-Chinese epoch, instead of the Yanshan epoch as suggested in the geological report of the Xingguo unit in a scale of 1/200000. Combining with the reports of other Indosinian granites in the Nanling district, it was concluded that Indo-China movement had a great effect in the Nanling district and produced larger scale magmatic activity with more outcrop areas than was previously understood. The higher latitude of Huagnsha intrusion further indicated the intrusions described in the geological report of Xingguo, Jinggangshan, and even the Ninghua unit in a scale of 1/200000 also have the potential to host ion adsorption type REE deposits, which should be significant for ore prospecting.