相山铀矿田邹家山矿床英安斑岩脉锆石U-Pb年代学、地球化学、Hf同位素组成及其地质意义

对首次在相山铀矿田邹家山矿床发现的英安斑岩脉开展了岩石地球化学、锆石U-Pb年代学和Hf同位素地球化学研究.LA-ICP-MS锆石U-Pb年龄测试结果表明:两个英安斑岩脉样品年龄加权平均值分别为122.4±0.5 Ma和126.5±1.4 Ma，晚于相山大规模火山侵入活动时间(132~137 Ma).该岩脉具有明显的轻重稀土分馏、负Eu异常的特征，大离子亲石元素明显富集，Nb、Ta显示明显的负异常，锆石ε_Hf(t)值为-22.0~0.2，且大多数集中在-6~-10之间，两阶段Hf模式年龄t_DM2为1.17~2.58 Ga.相山英安斑岩脉的地球化学特征与相山火山岩、次火山岩具有一定相似性.微量元素和锆石Hf同位素分析结果显示，英安斑岩脉主要为硅铝质地壳物质的部分熔融形成，但不排除有地幔物质的混入.邹家山英安斑岩脉以及同时期的中基性脉岩很可能形成于早中白垩世时期的太平洋俯冲板片持续后撤引起的岩石圈伸展环境，是典型张性构造应力体制的产物. 

Zircon U-Pb Geochronology,Geochemistry and Hf Isotopic Compositions of Dacitic Porphyry in Zoujiashan Deposit of Xiangshan Uranium Orefield and Its Geological Implication

Geochemistry,zircon U-Pb geochronology and Hf isotopic compositions of dacitic porphyry discovered in the Zoujiashan deposit were studied for the first time in Xiangshan uranium deposit. The LA-ICP-MS zircon U-Pb age testing results show that the average weighted age of two samples collected from underground tunnel and open pit were 122.4±0.5 Ma and 126.5±1.4 Ma,respectively,which were formed much later than the large-scale volcanic-intrusive activity. The rock is characterized by negative Eu anomalies,light-heavy REE fractionation,enrichment of large lithophilic elements as well as negative anomalies in Nb and Ta. The zircon ε_Hf(t) values range from -22.0 to 0.2,most of which are concentrated between -6 and -10,and the two-stage Hf model age t_DM2 range from 1 170 to 2 575 Ma,which share the similar characteristics with the Xiangshan volcanic rocks and subvolcanic rocks. The trace element and zircon Hf isotopic analysis showed that the dacitic porphyry was mainly derived from partial melting of crust material,but the participation of mantle material could not be ruled out. In combination with previous data,it is believed that the dacitic porphyry and the intermediate-basic dikes were probably formed in the lithospheric extension environment caused by the continuous retreat of the Pacific subduction plate during the Early-Middle Cretaceous period,and were the typical products of the lithospheric thinning in South China.