Zircon SHRIMP U-Pb Age of Gaojian Group in the South-eastern Margin of Yangtze Craton
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摘要: 分布在凯里-怀化-溆铺-双峰-衡阳-萍乡一线以南,叠覆于武陵运动界面之上的陆缘斜坡-盆地相沉积被称为高涧群或下江群,被认为属板溪群的同期异相沉积。但迄今为止却还没有直接在高涧群底部获得可靠的年龄数据,以致二者的时限及对应关系难以确认。本文通过高涧群石桥铺组玄武-安山质火山角砾岩的采样分析,获得锆石SHRIMP U-Pb年龄828.8±9.6 Ma,与相当层位的湖北花山群底部的层状玄武岩SHRIMP U-Pb年龄824±9 Ma基本一致。因此,推断扬子东南缘沉积盆地从武陵造山运动结束至裂谷作用启动这一转换过程的时间点可能在830Ma左右。这一认识为扬子东南缘裂谷盆地演化与充填序列由南东向北西形成依次超覆的“楔状地层”模式提供了有力的约束性证据。
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关键词:
- 同位素年龄 /
- 玄武-安山质火山角砾岩 /
- 石桥铺组 /
- 高涧群 /
- 扬子东南缘
Abstract: Gaojian Group or Xiajiang Group which distribute in the south of Kaili - Huaihua - Xupu -Shuangfeng- Hengyang- Pingxiang and overstep in the motion interface of Wuling was formed in continental margin slopes- sedimentary basins. It also belongs to the different sedimentary phase in the same period of Banxi Group. But it still has no reliable age data obtaining directly from the bottom of Gaojian Group so far so that their time limit and their corresponding relation are difficult to confirm. By the sample analyzing of the volcanic breccia of Xuanwu-Anshanzhi in Shiqiaopu Formation Gaojian Group, the author gets that the SHRIMP U-Pb age of 828.8±9.6Ma, which is consistent with the SHRIMP U-Pb age of 824 ± 9 Ma of layered basalt from the bottom of Huashan Group in Hubei. So we can infer that the shifting time from the ending of the Wuling Orogeny to the starting of rifting function in the evolution process of southeastern margin of Yangtze may be about 830 Ma. It pro-vided strong evidence for the basin evolution in the southeastern margin of Yangtze and the sequence overriding the model of wedge formation from southeast to northwest successively. -
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