摘要
我国西南地区广泛分布着中-下三叠统海相(包括盆地相、斜坡相及台地相)沉积地层和多层凝灰岩。通过采用锆石LA-ICP-MS U-Pb测年方法,对黔西地区沙窝剖面和彝良柳溪剖面中/下三叠统界线上凝灰岩首次进行了锆石微区同位素定年,分别获得界线年龄为247.2±2.4Ma(2σ,MSWD=0.85)和247.4±1.4Ma(2σ,MSWD=0.51),界定了"黔中隆起"及北部坳陷区中/下三叠统界线时限,此年龄结果与国际地层年代表(2018版)建议的奥伦尼克阶/安尼阶(Olenekian-Anisian)界线年龄247.2Ma以及贵州关刀剖面Olenekian-Anisian界线附近凝灰岩锆石TIMS年龄247.2±0.1Ma高度吻合。凝灰岩岩石地球化学特征显示出富集K2O、MgO,具明显负铕异常的特征,其物源可能来自古特提斯洋俯冲作用形成的大陆岩浆弧。幕式的火山活动可能是导致早-中三叠世生态环境间歇性恶化和生物迟滞复苏的重要原因,而深化对三叠纪幕式岩浆活动的认识,为我国西南地区三叠纪地层划分对比、构造演化以及探索三叠纪生物复苏-辐射与生态系统协同演化等提供依据。
The Middle and Lower Triassic marine facies(including basin facies, slope facies and platform facies) sedimentary strata and multilayer tuff are widely distributed in Southwest China. Zircon LA-ICP-MS U-Pb dating was firstly carried out for the tuff from the Middle/Lower Triassic boundary of the Shawo section in the Qianxi area and Liuxi section in the Yiliang areas, yielding the boundary ages of 247.2±2.4 Ma(2σ, MSWD=0.85) and 247.4±1.4 Ma(2σ,MSWD=0.51), respectively. The time limit for the Middle/Lower Triassic boundary in the Center Guizhou Uplift and the northern depression area was determined, and coincides with the age of 247.2 Ma for the Olenekian-Anisian boundary suggested by the International Chronostratigraphic Chart(2018 edition) and the TIMS age of 247.2±0.1 Ma of the tuff near the Olenekian-Anisian boundary in Guandao section, Guizhou Province. The geochemical characteristics of tuff rocks show K2O and MgO enrichment and obvious Eu negative anomaly, indicating that the tuff may be derived from the continental magma arc formed by the ancient Tethys subduction. The episodic volcanism may be an important cause responsible for the intermittent deterioration of the ecological environment and the delayed biotic recovery in the Early-Middle Triassic. The result of this study will deepen the understanding of the Triassic episodic magma activity, and provides a basis for the Triassic stratigraphic division, tectonic evolution and exploration of the Triassic biorecovery-radiation and ecosystem co-evolution in the southwestern China.
作者
任光明
朱同兴
庞维华
王立全
金灿海
卢君勇
文俊
张鹏
周洋
REN Guangming;ZHU Tongxing;PANG Weihua;WANG Liquan;JIN Canhai;LU Junyong;WEN Jun;ZHANG Peng;ZHOU Yang(Chengdu Geological Survey Center of China Geological Survey,Chengdu、610081;Na 207 Geological Tern of Sichuan Bureau of Geology&Mineral Resources,Leshan,Sichuan,614000)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2019年第11期2770-2784,共15页
Acta Geologica Sinica
基金
中国地质调查局项目(1212011085147、DD20190054)资助成果