论文部分内容阅读
张士英岩体位于华北地台南缘,岩石类型包括钾长花岗岩、似斑状花岗岩和石英斑岩脉,其中只在钾长花岗岩中发育有暗色岩石包体,在包体和寄主岩中发育反映岩浆混合作用的岩石结构。钾长花岗岩、似斑状花岗岩和石英斑岩脉的SHRIMP锆石U-Pb年龄分别为107.3±2.4Ma、106.7±2.5Ma和101±3Ma。锆石Hf同位素分析结果显示,钾长花岗岩的锆石εHf(t)为-15.96～-20.80,单阶段模式年龄(tDM1)为1396～1643Ma,两阶段模式年龄(tDM2)为1880～2018Ma;似斑状花岗岩的锆石εHf(t)为-18.97～-22.18,tDM1为1512～1640Ma,tDM2为1925～2080Ma;除了一粒年龄为2.6Ga的锆石具有εHf(t)为-0.71、tDM1为2943Ma和tDM2为3036Ma的组成,石英斑岩的锆石εHf(t)为-23.41～-27.95,tDM1为1678～1896Ma,tDM2为2144～2330Ma。这些数据暗示,除了存在少量太古宙地壳物质的贡献外,张士英岩体的物质来源可能主要为1.9～2.3Ga期间形成的新生地壳,但也不排除古老地壳与富集地幔源混合的可能。综合分析前人研究成果表明,在太平洋板块俯冲方向发生转变的过程中,先存断裂带发生拉张。张士英岩体与中国东部同期岩浆活动一起可能形成于这种受断裂带控制的伸展环境。
The rocks are mainly composed of potash-bearing granite, porphyritic granite and quartz porphyry veins. Among them, dark-colored rock inclusions are only developed in the potash-bearing granite, and the magma mixture is developed in the enclaves and host rocks The role of rock structure. The SHRIMP zircon U-Pb ages of potash-bearing granite, speckled granite and quartz porphyry are 107.3 ± 2.4Ma, 106.7 ± 2.5Ma and 101 ± 3Ma, respectively. The results of Hf isotopic analysis of zircons show that the εHf (t) of zircon from the potash-bearing granites is from -15.96 to -20.80, the single-stage model (tDM1) is from 1396 to 1643Ma and the tDM2 is from 1880 to 2018Ma. The porphyritic zircons have εHf (t) of -18.97 to -22.18, tDM1 of 1512 to 1640Ma and tDM2 of 1925 to 2080Ma. Except for a zircon 2.6Gb age zircon with εHf (t) of -0.71 and tDM1 of 2943Ma And tDM2 is 3036Ma. The zircon εHf (t) of quartz porphyry is -23.41 ~ -27.95, tDM1 is 1678 ~ 1896Ma, and tDM2 is 2144 ~ 2330Ma. These data suggest that except for the contribution of a small amount of Archean crustal material, the material sources of the Zhangshi porphyry probably originated from the new crust formed during the period of 1.9 ~ 2.3Ga, but the possibility of mixing the ancient crust with the enriched mantle source is also not ruled out. Comprehensive analysis of previous research results show that in the Pacific plate subduction direction of the transformation process, the occurrence of pre-existing tensile fracture. Together with the magmatic activities in the same period of eastern China, the Zhang Shiyang massif may be formed in such an extensional environment controlled by the fault zone.