塔西南叶城地区新生代沉积物源分析:来自碎屑锆石U-Pb年代学证据

新生代以来,受印度与欧亚板块碰撞和持续汇聚作用的影响,西昆仑造山带重新活化,并向塔里木盆地强烈挤压冲断,形成塔西南新生代再生前陆盆地。本文以塔西南叶城地区柯克亚剖面新生代砂岩样品为研究对象,进行碎屑锆石LA-MC-ICP-MS U-Pb测年,探讨其主要物源方向,以期对西昆仑隆升历史进行约束。结果表明,碎屑锆石的年龄存在70 Ma,200~500 Ma,800~1000 Ma,1600~2000 Ma和2400~2800 Ma五个年龄段,反映了该区物源的复杂性。综合分析潜在的物源区岩石属性、年龄构成及古流向等研究资料,认为物源区主要包括铁克里克、奥依塔克及喀喇昆仑地区,来自西南天山的可能性比较低。其中70 Ma的碎屑锆石主要来自于南部的帕米尔和喀喇昆仑地区;而200~500 Ma年龄段的锆石来自南部的铁克里克和西南部奥依塔克地区,这两个地区是主要的物源区;800~1000 Ma年龄段的锆石主要来自库地缝合带;1600~2000 Ma和2400~2800 Ma年龄段的锆石主要来自于铁克里克地区的前寒武纪结晶基底。研究区与奥依塔克地区位于同一弧形带,二者具有相似的物源区。上新世阿图什组地层沉积前后锆石形态具有明显突变,代表了西昆仑一次快速隆升过程。

Provenance of Cenozoic Sediments in Yecheng,Southwest Tarim Basin:Constraints from Detrital Zircons U-Pb Geochronology

The west Kunlun Orogen reactivated and thrusted to the Tarim basin in the Cenozoic due to the collision between the India and Eurasia blocks. In order to research the uplift history of the western Kunlun and the main provenance of the Southwest Tarim basin, geochronological features of detrital zircons from the Cenozoic sandstone at the Kekeya profile near Yecheng District were analyzed using LA-MC-ICP-MS method. The five peaks of detrital zircon U-Pb ages of <70 Ma, 200?500 Ma, 800?1000 Ma, 1600?2000 Ma, 2400?2800 Ma, suggest a complex provenance. The probable source areas include the Tiekelike Mountains, Oytag, and Karakorum, and less likely the Southwest Tianshan Mountains. We concluded that the detrital materials of <70 Ma period were mainly from the southern Pamir and Karakorum areas; 200?500 Ma period from the Tiekelike and southwest Oytag; 800?1000 Ma period from the Kudi suture;1600?2000 Ma and 2400?2800 Ma periods mainly from the Precambrian crystalline basement in the Tiekelike area. Cenozoic sediments in the study area may have a provenance similar to that of the Oytag area in the same arc belt. The sudden changes in morphological features of detrital zircons before and after the sedimentation of the Pliocene Atushi Formation might have resulted from the rapid uplift of the western Kunlun in the Pliocene.