阿尔金山脉新生代剥露历史——前陆盆地沉积记录

    Cenozoic erosional history of the Altyn Tagh Mountains inferred from the sedimentary record of the foreland basin

    • 摘要: 新疆且末县江尕勒萨依盆地位于阿尔金山脉的北西山前,其内连续沉积了中生代一新生代地层。盆地内古新统一始新统为河流相沉积;渐新统至中新统为山麓河流相灰色砾岩和棕色砂岩;上新统为山麓洪积相砾岩夹泥岩;下更新统全为砾岩层。岩性组合特征及其砂岩碎屑、砾石组分变化规律,反映出阿尔金山脉的新生代剥蚀历史:古近纪早、中期,阿尔金山脉的地形高差小,古生界双峰式火山岩首先被剥蚀;至渐新世末一中新世早期,山脉高差加大,基底元古宇开始出露地表被剥蚀;中新世末期,山脉高差进一步加大,剥蚀速率加快;至第四纪早期西域砾岩开始沉积时,地形高差加剧,中、古元古界开始暴露被剥蚀。区域资料分析表明,阿尔金山脉在新生代具有多期次阶段性隆升的特征,存在3期次快速隆升事件:渐新世末一中新世早期、中新世晚期(大约8Ma)和第四纪早期。

       

      Abstract: The Janggalsay basin, Qiemo County, Xinjiang, is located in the northwestern front of the Altyn Tagh Mountains, where Meso-Cenozoic sediments are continuously deposited. The Paleocene to Eocene inside the basin are fluvial sediments; the Oligocene to Miocene are piedmont fluvial brown conglomerates and brown sandstones; the Pliocene is piedmont diluvial conglomerates with mudstones; the lower Pleistocene is all composed of conglomerates. The characteristics of the lithological associations and variation in composition of detritus in sandstone and pebbles in conglomerate reveal the erosional history of the Altyn Tagh Mountains. Paleozoic bimodal volcanic rocks were firstly eroded during the Paleocene to Eocene, and the topographic height difference between the Altyn Tagh Mountains and the Janggalsay basin was small. This difference became large during the late Oligocene to early Miocene, and the Proterozoic basement was exposed subseguently and eroded. The denudation ration increased at the end of the Miocene. The Lower to Middle Proterozoic basement rocks were exhumed to the surface till the Early Pleistocene when the Xiyu Formation began to deposit. Analysis of regional data indicates that the Altyn Tagh Mountains were uplifted by stages and experienced three rapid uplift events in the Cenozoic, i.e. from the terminal Oligocene to early Miocene, in the late Miocene (Ca 8 Ma BP) and early Quaternary.

       

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