赣南部分岩体的锆石铀-铅同位素年代学研究及其对成岩成矿机制的再认识

U-Pb Isotopic Age and a Further Understanding of the Ore-forming Mechanism in Granite from the Southern Jiangxi Province

赣南岩浆岩分布广泛,有的岩体成岩时代明确,有的则存在争议。利用激光多接收器电感耦合等离子体质谱(LA-MC-ICPMS)技术测定了田新、路迳、水头、白鹅、高山角、韩坊、杨村、湖南洞、珠兰埠、淋洋、大富足、油山、吉埠黄沙、阳埠和万田等岩体的U-Pb年龄,表明这些岩体不全是燕山期形成的,即使是燕山期的田新、路迳、水头、白鹅、韩坊、杨村等岩体中也存在有更早期的锆石,大部分岩体经历了6～10 Ma的结晶成岩历史。通过与以往K-Ar、Rb-Sr等时线方法的初步对比,指出赣南地区花岗岩虽然在同位素年龄数据上以侏罗纪为多,但印支期的岩体面积不小,前寒武纪和加里东期的信息也不断增多,说明赣南花岗岩型地壳的演化经历了漫长的历史过程,相当一部分岩体不是单一成岩期形成的,而是多期次多阶段形成的。加里东期的岩体以往不被注意,认为与钨矿关系不密切,但可以成为离子吸附型稀土矿的成矿母岩。

Magmatic rocks in the Southern Jiangxi are widely distributed. The diagenetic ages of some rocks are clear, but are still in dispute for others. The U-Pb ages of the Tiauxin, Lujing, Shuitou, Bale, Gaoshanjiao, Hanfang, Yangcun, Hunandong, Zhulanbu, Linyang, Dafuzu, Youshan, Huangsha, Yangbu, Wantian and other granites were obtained by using Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometry （LA-MC-ICPMS）. The data show that these granites did not all intrude in the Yanshanian stage. Although the Tianxin, Lujing, Shuitou, Bale, Hanfang, Yangcun and some granites intruded mainly in the Yanshanian stage, they hosted some earlier zircons, which means most of the rocks experienced a 6 - 10 Ma crystallization rock- forming history. By comparing with K-At and Rb-Sr geochronologies, the granites in the Southern Jiangxi mainly intruded during the Jurassic era. However, areas of Indosinian rocks are substantial, in addition to there being more and more petrogenic information in the early Cambrian and Caledonian eras. All the research results indicate that granites in the Southern Jiangxi experienced a long term evolution and many of them were formed in multiple stages. Although Caledonian rocks were ignored previously since they had no relationship with W deposits, they can be primary rocks for ion-adsorption type rare earth element deposits.