摘要
长安组为扬子地块东南缘确认的一套冰源相碎屑沉积,其精确沉积时限对于了解华南新元古代冰期的起点时间和演化历程具有重要意义。以往限于定年技术的精度和测试对象的稀缺,长安组的年龄一直少有报道。最近在湘中新化县碧溪地区发现长安组下部存在沉凝灰岩夹层,获得了大量岩浆型锆石,对其进行了高精度锆石LA-ICP-MS与SHRIMP U-Pb同位素年代学对比研究。结果表明,其锆石206Pb/238Pb加权平均年龄分别为(751±5),(764±10)Ma。综合分析相关地层的最新年龄数据可以确定,长安组可与西北地区同期沉积以及澳大利亚Sturtian冰期的年龄进行比较。沉积旋回分析表明,长安组底部沉积物具有典型的重力流特征,沉积速率较大。结合相关地质证据分析认为,长安组的底界年龄置于760Ma较为合适。
Chang＇an Formation in the southeastern Yangtze, craton confirmed a ice-source clastic deposit. It is important that it＇s dating accurately to understand South China Neoproterozoic glaciations and evolu- tion. As limit of dating techniques and test objects scarcity,age of Chang^an Formation has been rarely re- ported. The author recently discovered tuff mezzanine, magmatic zircon in lower Chang＇an Formation in Bixi area,central Hunan. By LA-ICP-MS and SHRIMP U-Pb isotope chronology study, the results show that the zircon 206Pb/238pb weighted average age of 751±5,764±10 Ma. Comprehensive analysis of the lat- est relevant stratigraphic age, Changr an Formation can compare the age and the Northwest Territories, Australia Sturtian glaciation. The sedimentary cycle analysis showed that bottom of Changan Formation are typical gravity sediments. The age of the lower boundary of the Changran Formation is more appropri- ate 760 Ma.
出处
《地质科技情报》
CAS
CSCD
北大核心
2014年第2期15-20,27,共7页
Geological Science and Technology Information
基金
国家自然科学基金重点项目(41030315)
中国地质调查局项目(1212011121108)
关键词
长安组
同位素年龄
南华纪
扬子地块东南缘
Chang＇an Formation isotope age
Nanhuaian
southeastern Yangtze craton
