扬子板块西缘中生代—新生代碰撞造山事件的记录:来自峨眉山玄武岩的锆石U-Pb同位素证据

利用LA-ICP-MS测定技术,对扬子板块西缘滇东倘甸一带的峨眉山玄武岩中的锆石进行了U-Pb同位素年龄测定,363个年龄数据的分布范围为(14.9±0.6)~(3 023±50) Ma,跨越地质时代长,其11个年龄峰值为750~850 Ma、~450 Ma、~275Ma、~260 Ma、~247 Ma、~215 Ma、~160 Ma、~120 Ma、~100 Ma、~52 Ma及~35 Ma,反映了峨眉山玄武岩在形成过程中经历地壳物质的混染,形成后受到了后期构造热事件的巨大影响。其中峨眉山玄武岩一、二亚旋回分别形成于(259.9±3.2) Ma及(259.2±3.6) Ma,~275 Ma的玄武岩锆石年龄可能代表峨眉山玄武岩岩浆房的形成年龄及峨眉地幔柱事件导致地壳开始隆升的时间,峨眉山玄武岩形成后,扬子板块西缘依次经历了~247 Ma、~215 Ma、~160 Ma、~120 Ma、~100 Ma、~52 Ma、~35 Ma的构造热事件,这些年龄数据是扬子板块西缘中生代—新生代碰撞造山事件达到温压高峰的时间记录。

Records of Mesozoic-Cenozoic Collision Orogenic Events on the Western Margin of the Yangtze Platform:Geochronology Evidence from Zircon U-Pb Isotope of Emeishan Basalt

Using LA-ICP-MS technique,the U-Pb isotope determination of zircons in the Emeishan basalts in Tangdian, of eastern Yunnan on the western margin of the Yangtze Plate is carried out. The distribution range of 363 age data is (14.9±0.6)-(3,023±50) Ma, spanning a long geological age, its 11 age peaks are 750~850 Ma, ~450 Ma, ~275 Ma, ~260 Ma, ~247 Ma, ~215 Ma, ~160 Ma, ~120 Ma, ~100 Ma, ~52 Ma and ~35 Ma, respectively, reflecting that Emeishan basalt experienced the contamination of crustal materials in the formation process, and being affected by later tectonic thermal events. The first and second sub-circle of the Emeishan basalt were formed at (259.9±3.2) Ma and (259.2±3.6) Ma, respectively. The zircon ages of the basalts of ~275 Ma may represent the age of the formation age of Emeishan basalt magma chamber and the time when the crust began to uplift due to Emei mantle plume event.After the formation of the Emeishan basalt, the western margin of the Yangtze Plate experienced successively tectonic thermal events of ~247 Ma, ~215 Ma, ~160 Ma, ~120 Ma, ~100 Ma, ~52 Ma, and ~35 Ma. These age data are the time records of the Mesozoic Cenozoic collision orogenic event reaching the peak of temperature and pressure on the western margin of the Yangtze Plate.