摘要:
华南地区新元古代地层区域上涉及中国上、下扬子地区,包括中国地层表中的青白口系、南华系和震旦系,时代上分别对应国际地层年代表中拉伸系、成冰系和埃迪卡拉系。传统划分是以晋宁运动(四堡运动)为标志划分为中元古界和新元古界,近年来,通过地层中凝灰岩锆石SHRIMP U-Pb的测定,华南地区新元古代年代表已进行了有效年代学标定,突出了地层对比的可靠性和新的构造观点解译。华南古陆构造演化研究需要以构造为纲,明确了古陆周缘地层发育了中元古代晚期相关沉积记录,而华南古陆内部,特别是江南造山带为武陵运动的构造运动产物。本文将报道桂西地区青白口系拱洞组底部SHRIMP锆石U-Pb年代学测定数据(799.8±5.5) Ma,江西与湖南交界长安组底部获得凝灰岩锆石年龄(770±10) Ma,湘西北长安组底部获得凝灰岩锆石年龄(758.6±5.4) Ma和湾溪口村长安组冰碛岩距底部十多米处获得凝灰岩锆石年龄(743.8±4.1) Ma。上述年龄进一步提供华南地区冰碛岩地层的年代学依据。
Abstract:
Neoproterozoic strata in South China consist of Qingbaikouan, Nanhuan and Sinian systems in Chinese Time Scale which can be respectively correlated with Tonian, Cryogenian and Ediacaran systems in the International Time Scale. The South China area is subdivided into two parts, i.e., Upper and Lower Yangtze blocks. Traditionally, the Jinning Movement or Sibao Movement is regarded as the marker for the boundary between the Mesoproterozoic and the Neoproterozoic. In recent years, the SHRIMP U-Pb determination of the tuff zircons from the strata has yielded effective dating data for chronology of Neoproterozoic strata, which give prominence to the reliability of the stratigraphic correlation and add interpretation of new tectonic viewpoints. We should take the tectonic as the key to tectonic evolution studies so as to reconfirm the depositional records of Late Mesoproterozoic on the margin of South China. However, the Sibao movement is a late orogeny in the interior of South China old land. The new chronostratigraphic data promote tectonic division, stratigraphic correlation and understanding of stratabound deposits. At the same time, a framework will contribute to the stratigraphic correlation of global and continental blocks. In this paper, the authors present the SHRIMP zircon U-Pb data ((799.8±5.5) Ma) obtained at the bottom of Qingbaikouan Gongdong Formation in western Guangxi, the SHRIMP zircon U-Pb age of (770±10) Ma for the Chang’an Formation in Jiangxi- Hunan border area, the SHRIMP zircon U-Pb age of (758.6±5.4) Ma for the bottom of the Chang’an Formation in western Hunan, and the SHRIMP zircon U-Pb age of (743.8±4.1) Ma for the strata 10 m above the bottom of the Chang’an Formation at Wanxikou Village. These data further provide the geochronologic basis for dismictite strata in South China.
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