松潘-甘孜盆地中、晚三叠世沉积物来源及演化的锆石U-Pb年代学制约

从松潘-甘孜构造带东北部若尔盖盆地的红参一井内分别采取中三叠世晚期和晚三叠世早期的砂岩样品,用激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)方法对其中的碎屑锆石颗粒进行了U-Pb年龄分析,结果显示锆石形成年龄的范围在2432 741 Ma间,主要峰值集中在240～290,400～480,1 800～2 000,2 200～2 500 Ma.通过对碎屑锆石年龄分布特征的研究,并结合古水流条件的约束,认为松潘-甘孜盆地东部中、晚三叠世沉积盖层内形成于240～290 Ma和400～480 Ma的锆石分别来自东昆仑南部和北秦岭,形成于1 800～2 000 Ma和2 200～2 500 Ma的锆石来自华北板块.由不同时期沉积物中碎屑锆石年龄分布特征的变化表明:晚三叠世中期以后有更多扬子板块的物质进入了松潘-甘孜盆地,使盆地内沉积物的组合发生了明显的改变,这样的变化反映了晚三叠世中期以后扬子板块西缘存在一个快速抬升的过程.

U-Pb Constraints on Provenance and Evolution of Middle to Late Triassic Sediment in Songpan-Garze Basin

Some sandstone samples, formed in the late period of Middle Triassic and early period of Late Triassic, were collected from Hongcan Well in Zoige Basin, located in the northeast of Songpan-Garze terrain. The U-Pb age of detrital zircons contained in the sandstone samples were analyzed by LA-ICP-MS method. The detrital zircons are aged in a wide range, varying from 243 to 2741 Ma, with the main populations ranging from 240-290 Ma, 400-480 Ma, 1 800-2000 Maand2 200-2 500 Ma. Through the ages distributing of detrital zircons and the constraints from paleocurrent, it can be concluded that the detrital zircons, formed in 240-290 Ma and 400-480 Ma, are from East Kunlun and North Qinling respectively and those formed in 1 800-2 000 Ma and 2 200-2 500 Ma, are from North China Block. The age distribution change of detrital zircons from the sediment formed in different periods also indicates that more substances from Yangtze block entered Songpan-Garze Basin from the middle period of Late Triassic, so the composition of sediment must have been altered obviously. Also the evolution of the basin sediment provenance implies that a rapid elevation of West Yangtze block occurred after the middle period of Late Triassic.