江西相山铀矿田河元背地区流纹斑岩地球化学、锆石UPb年龄及HfSrNd同位素特征
Geochemistry, Zircon UPb Geochronology and HfSrNd Isotopic Characteristics of the Rhyolite Porphyry at Heyuanbei in Xiangshan Uranium Orefield, Jiangxi Province

摘要： 在江西相山铀矿田河元背地区实施的CUSD3钻孔，发现其深部存在晚期侵入到打鼓顶组流纹英安岩、凝灰岩、泥质粉砂岩中的流纹斑岩。利用激光等离子质谱分析技术(LAICPMS)测得流纹斑岩的锆石206Pb/238U年龄为(1318±07)Ma (MSWD=041)，晚于前人所测的鹅湖岭组碎斑流纹岩年龄。该流纹斑岩具有高硅、富钾、铝过饱和等特点，还表现出高场强元素Rb、Th、U、La、Ce、Nd和LREE富集，Ba、Nb、Sr、P、Ti等元素亏损以及δEu明显负异常的特点。锆石的εHf(t)值介于 -677~-1038之间，对应的二阶段Hf模式年龄TDMC介于1 619~1 846 Ma，岩石的ISr值为0710 92~0712 01，εNd(t)值为-818~-919。其稀土元素、微量元素分布模式及同位素特征与前人报道的碎斑流纹岩特征类似，暗示流纹斑岩与碎斑流纹岩具有相同的物质来源。以上特征说明河元背地区流纹斑岩形成于早白垩世造山运动碰撞后伸展阶段，为深部硅铝质地壳部分熔融的产物。相山西部流纹斑岩的发现，可以推测该区或许存在一个次级火山机构。
Abstract: A suite of rhyolite porphyry was found at Heyuanbei in Xiangshan uranium orefield of Jiangxi Province, which intruded into the rhyodacite, tuff, argillaceous siltstone. LAICPMS UPb isotopic dating on zircons from the rhyolite porphyry yields magmatic crystallization age of (1318±07) Ma (MSWD=041). The rhyolite porphyry is characterized by high in SiO2, K2O, Al2O3 and relatively low in MnO and P2O5. It is enriched in Rb, Th, U, La, Ce, Nd and light rare earth elements, depleted in Ba, Nb, Sr, P and Ti, and shown slightly negative Eu anomalies (δEu=021-025). The zircon εHf(t) values range from -677 to -1038, with Hf depleted mantle model ages (TDMC) between 1 619 and 1 846 Ma. The ISr values range from 0710 92 to 0712 01. And the εNd(t) values range from -818 to -919. The experimental results indicate that the rock was generated by partial melting of crustal rocks during extension in Lower Cretaceous. And a subvolcanic conduit may exist in the west of Xiangshan