赣南加里东期陡水岩体的锆石U-Pb年龄、地球化学特征及其稀土含矿性探讨

Zircon U-Pb Age, Geochemistry and Mineralization Prospective of the Caledonian Doushui Granitic Pluton in Southern Jiangxi Province

利用LA-MC-ICPMS对陡水岩体中细粒黑云母二长花岗岩中的锆石开展了U-Pb同位素测试,获得206Pb/238U年龄为460.8±1.5 Ma(n=10,MSWD=0.78),属华南加里东晚期第一次岩浆活动峰期的产物。陡水花岗岩显示高硅(SiO2平均含量为78.37%),富钾(K2O>Na2O)的特征,A/CNK平均值1.17,属于高硅高钾过铝质花岗岩。其稀土总量偏低(平均为90.68μg/g),稀土元素球粒陨石标准化配分图具有M型四分组效应,强烈的Eu负异常;明显亏损Ba、Sr、Ti、P元素。相对于已知含稀土矿的和具有寻找稀土矿潜力的加里东期岩体来说,陡水岩体可能不具备形成稀土矿的能力。通过对南岭地区已确认的加里东期花岗岩体的地球化学资料对比分析,认为华南地区加里东期花岗岩对离子吸附型稀土矿床的形成有很大贡献,在今后的找矿工作中应给予重视。

The Doushui granitic pluton situated in Shangyou county, Jiangxi province, is among the first recognized Caledonian granites in South China according to their geological occurrences, and no isotopic dating result has been reported yet. Zircon grains from the Doushui granite were analyzed using Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometer （LA-MC-ICPMS） method, which yield a U-Pb age of 460.8±1.5 Ma. This age confirms that the granite was intruded in the Middle Ordovician, which was products of the first peak period of magmatism during the Late Caledonian period in southern China, indicative of a new cycle of folding and orogen. Comparing with the other rare earth bearing Caledonian granitoids in the Nanling region, the Doushi granite is unlikely to form ion exchangeable REE deposit.