内蒙古狼山地区晚第四纪泥石流发育特征及其构造意义

内蒙古狼山山前断裂活动强烈,致使泥石流灾害发育,研究狼山山前泥石流的发育特征对深入了解晚第四纪以来狼山的构造抬升具有重要意义。通过对狼山山前泥石流堆积特征和地貌特征的调查,发现研究区内泥石流沉积物颗粒粗大,分选磨圆均较差,胶结及风化程度随年代的变老而变强,山前堆积台地从老到新由上到下呈阶梯状排列。利用光释光(OSL)对厘定的4期古泥石流堆积进行测年,4期泥石流分别形成于113.33±12.31ka BP、65.33±6.71ka BP、34.67±3.52ka BP、5.00±0.57ka BP,进而计算出4期构造活跃期狼山中段的平均下切速率分别为0.44m/ka、0.93m/ka、1.11m/ka、2.8m/ka。水流下切速率的增加来源于构造隆升的驱动,由此表明狼山晚第四纪以来可能处于一个加速隆升的阶段;113.33ka以来水流下切速率的空间分布揭示了狼山中段存在隆升速率由西高东低向东高西低转换的特点。本研究对重建晚第四纪阴山西段隆升过程和河套盆地古地理格局具有重要意义。

Development features of the Late Quaternary debris flow and their tectonic significance in Langshan area, Inner Mongolia

The Langshan Mountain of Inner Mongolia is located in the western segment of Yinshan orogenic belt and on the northwestern margin of Ordos Block ring structure belt. Tectonic activities in this region were widely existent, which caused extensive debris flows in the piedmont zone. The study of development features of the Late Quaternary debris flow in Langshan area is very important for understanding the tectonic uplift. The authors investigated debris flow deposition characteristics and landscape features of the Langshan area and found that debris flow sediment particles are coarse, poor sorting and rounding. Their cementation and weathering degree is stronger along with the aging. Piedmont accumulation platforms from old to new are ladder shaped from top to bottom. The authors divided them into 4 sequences. And the Optically Stimulated Luminescence (OSL) dating shows that they were formed respectively at 113.33±12.31ka BP, 65.33±6.71ka BP, 34.67±3.52ka BP, and 5.00±0.57ka BP. Then the authors calculated the average incised rate of the four tectonic active periods in the middle of Langshan Mountain, which is respectively 0.44m/ka, 0.93m/ka, 1.11m/ka and 2.8m/ka. The increase of the incised rate results from the driving of tectonic uplift, which suggests that tectonic uplift of Langshan Mountain may have been in a stage of accelerating uplift since Late Quaternary. The spatial distribution of the incised rate reveals the feature that the uplift rate was from high in the west and low in the east to high in the east and low in the west since 113.33ka in the middle of Langshan Mountain. This study has important significance for the reconstruction of uplift process of Late Quaternary Yinshan orogenic belt and the palaeogeographic pattern of Hetao Basin.