阿尔金断裂带东段晚更新世阶地沉积物红外释光测年及其构造意义

OPTICAL STIMULATED LUMINESCENCE (OSL) DATING OF LATE PLEISTOCENE TERRACE DEPOSITS IN THE EASTERN SEGMENT OF THE ALTYN TAGH FAULT AND ITS TECTONIC IMPLICATION

对流经阿尔金断裂带东段的段家沙河、疏勒河和踏实河的阶地沉积物进行了细颗粒多测片红外释光(IRSL)测年,初步确定了晚第四纪各级阶地的形成年代和构造抬升速率。疏勒河在昌马盆地南缘发育7级阶地,光释光测年结果显示这些总高度超过100m的阶地可能主要形成于数万年以内,抬升速率约为2.5mm/a;照壁山峡谷疏勒河保留有5级阶地,大致形成于20万年前,阶地的抬升速率约为0.7mm/a;段家沙河在红柳峡上形成4级阶地,形成于距今7万年以来,其抬升速率约为06mm/a。

The ages of terrace deposits along the Shulehe River system are determined by the use of Optical Stimulated Luminescence (OSL) dating technique. The possible tectonic implications of the obtained age data are discussed as follows: (1) The Duanjiagou, Shulehe, and Tashihe Rivers are three rivers of different characters from the Shulehe River system. Several levels of terraces of different altitudes and corrosion rates were developed in the intermont basin and mountain front on the eastern segment of the Altyn Tagh fault. These terraces are the result of differential uplift of the fault blocks. (2) On the southern margin of the Changma basin, 7 levels of terraces were developed along the Shulehe River. OSL dating results show that those over 100m high terraces were formed mainly about 40,000 years ago, and this may indicate the intensive uplift of the Daxueshan Xiangmaoshan Mountains and the new activity of the Changma seismic belt. The rate of tilted uplift of the southern part of the Changma basin is inferred to be 2.5mm/a. (3) At Zhaobishan gorge, five levels of terraces of the Shulehe River are still well preserved. Among them, the T 3 terrace of 40～60m elevation above the stream level might be related to the new tectonic activity of the region. The T 5 terrace of over 150m elevation above the stream level observed at the boca has an ESR age of approximately 200ka and an uplift rate of 0 7mm/a. (4) On the Hongliuxia fault block uplift, 4 levels of terraces were developed along the Duanjiasha River. Dating results of the T 1 , T 2 and T 3 terraces show that a linear relation exists between the heights and the ages of the terraces, from which an uplift rate of 0.6mm/a can be deduced. The Hongliuxia and the Zhaobishan fault block uplifts are the fault blocks controlled by the strike slip movement of the Altyn Tagh Fault. They have approximately the same rate of uplift that is quite dif￣ferent from that of the range front uplift of the Daxueshan Xiangmaoshan Mountains, indicating that the uplift deformation of the Tibetan Plateau in the late stage of late Pleistocene occurred mainly along the Changma active fault zone. (5) Four levels of terraces were developed at the fan apex of the Tashihe River, and the age of the T 3 terrace is dated to be 78.8±5.5ka. It is postulated, therefore, that the terraces at the apex of the Tashihe River alluvial fan were formed in the middle to late stages of late Pleistocene. On the basis of OSL dating results of terrace deposits and the investigation of tectonic landforms, it is concluded that periodic uplift has occurred in the Nanjieshan fault block at 300 ka BP or during the middle to late stage of late Pleistocene.