青藏高原北部银石山地区古近纪盆-岭构造及形成机制

Oligocene basin-mountain structure and its forming mechanism in Yinshishan area,northern Qinghai-Tibet Plateau

研究区自北而南共发育8条东西或近东西走向的渐新世裂陷盆地,显示该时期具典型的盆岭构造格局。盆地代表性充填结构自北而南分别为以冲积扇相砾岩、扇三角洲相砂岩、浅湖相粉砂岩和泥岩、滨湖相为主的砾岩-砂岩-粉砂岩-泥岩组合,表明盆地北侧的单面断陷作用。狭长且边界较平直的形态特征、盆内同期基底断裂、盆地北侧山岭区中同期强烈的伸展构造变形、关水沟以西盆地北缘的沉积相变等,与盆地充填结构特征一道指示盆地的断陷构造属性。说明区域南北向拉张作用下的单剪伸展为盆-岭构造的直接形成机制;区内渐新世前后的岩浆作用及其所反映的地球动力学演化特征等,则指示盆-岭构造的深层动力学背景为岩石圈地幔甚至软流圈的向上隆起和顶托。

There occurred eight EW or nearEW Oligocene downfaulted basins in the Yinshishan area of northern QinghaiTibet Plateau,showing typical basinmountain tectonic framework.Representative sedimentary compositions in the basins from north to south are conglomerate of alluvialfan,sandstone of fandelta,siltstone and mudstone of shallow lake and conglomeratesandstonesiltstonemudstone assemble of bank lake,indicating singleside downfaulting in the northern sides of the basins.Long and narrow configuration,smooth and straight borders,existence of basemen faults in the basins,strong synkinematic extensional deformations in the northern mounts and change of sediments on the northern wedge of the Luoyinshan basin in east of Guanshuigou indicate downfaulted tectonic attribute of the basins.The abovementioned characteristics explain that SN simpleshear extension is the direct formative mechanism of the basinmountain structure;Magmatism and corresponding features of the earth's dynamic evolutions before and after Oligocene indicate that the uplift of the mantle asthenosphere is the deepseated dynamic background for forming of the basinmountain structure.