大同－阳原盆地南缘断裂带的晚第四纪分段和构造地貌变异

LATE QUATERNARY SEGMENTATION AND SEGMETED VARIATIONS IN TECTONIC GEOMORPHOLOGY OF SOUTHERN MARGINAL FAULT ZONE OF DATONG-YANGYUAN BASIN

大同－阳原盆地南缘断裂带是北京西北～山西北部盆－岭区的一条最大的断层。晚第四纪断层崖高度和高度分布型式把断裂带分为西南和东北两个段落。该断裂带在山前带和山麓坡的构造地貌、微地文期演化历史方面存在着明显的分段变异。构造地貌过程的速度和断层习性差异，以及段落边界的重叠断层特征，是构造地貌变异的直接原因。

The southern marginal fault zone of the Datong-Yangyuan basin is the largest fault in the basin-range area of NW Beijing-N Shanxi.Heights of late Quaternary fault-scarps and their a-long-striking distribution Pattern can divide the fault zone into two segments,the southwest(SW)segment and the northeast(NE)segment.Between these two segments there have been significant variations in mountain front and piedmont slope tectonic geomorphology.as well as in evolutional history of micro-physiographic stages.Individual segments have different quantitative mountain front geomorphobgical indices.Means of mountain front sinuosity(S).valley widthdepth relief ratio(Vf),and stream-gradient index(K)are 1.93,0.49 and 27.18,respectively,for the SW segment,wherea are1.57,0.39 and 56.61,respectively,for the NE segment.The SW segment piedmont slope is characterized by the landform assesbles of youngest alluvial fan A3(Q3+Q4)inerted into older fan A2(Q3),indicating that an upwarping of the near-fault part of older fan A3(Q3)might have occurred during late Quaternary.On the contrary,the NE segment peidmont slope is characterized by the landform assembles of youngest fan A3(Q+Q)overlapped onto oldest fan A1(Q3),showing that a downwarping might have occurred on the near-fault part of oldest fan A1(Q3).Before 36 8000a B.P,the NE segment might have experienced an evolutional history of erosion～aggradatin～erosion,while the SW segment minght have had evolutional stages of aggradation～erosion～aggradation.Tectonic geomorphological process rates,fault behavior,and segment boundary charateristics seem to be reasons of such segmented varations in tectonic geomorphology of the fault zone.During late Quaternary,the SW segment has a lower faulting rate relative to a fluvial downcutting rate,which were estimated to be 0.34mm/a and 0.41～0.48mm/a,resepectively.Displacement per event was averaged 0.9m ad recurrence interval was estimated to be 900～1000a.the NE segment has a higher faulting rate relative to a flurial downcutting rate,which were estimated to be 0.99mm/a and 0.22mm/a,respectively.Displacement per event was averaged 3.1m and recurrence interval was estimated to be 1800a.Furthermore,it is the overlapping faults between the SW segment and the NE segment to become the segment boundary,where a tectonic effect of displacement deficit might have occurred,playing and important role in such segmented variations in tectonic geomorphology.