西秦岭北缘-拉脊山两侧地貌差异及地貌演化

摘要

The northern margin of West Qinling-Lajishan Fault is reckoned as an important geomorphologic and geological boundary.The elevation and local relief differences between the two sides of the boundary are distinct.The aim of this study is to understand the topographic differences and morphologic evolution mechanisms between the eastern and the western side of the northern margin of West Qinling-Lajishan Fault.The digital elevation model combined with geologic data has been used to:1) Extract local relief and swath profiles to quantitatively reveal the topographic characters of the eastern and the western side of the boundary; 2) Make statistics on the elevation modes of the Cenozoic sandstones on both sides of the fault.The results show that the older strata lie at higher elevations in the eastern region of the boundary; And for the west of the boundary,older strata (Paleogene and Neogene)perch on lower elevations,however,the Quaternary strata lie in the lowest elevation.The differential topographic evolution history of the two sides of the boundary indicates the complexity of Cenozoic strata development.Moreover,the lithological combination and sedimentary facies of the Cenozoic strata in the eastern and western side of the northern margin of West QinlingLajishan boundary are summarized,and the denudation and aggradation history of the two sides of the boundary are compared in this study.A longer constant denudation history in the eastern side than the western side has been suggested.The results also indicate the differential tectonic evolution history between the two sides of the boundary.Outward growth of the Tibetan plateau appears in the eastern side.The deformation and uplifting decrease as propagating northeastward.For the western side,the deformation pattern is more complex with different evolution histories of faults under stronger compression.The limited river erosion has enhanced the up-growth of this part of the plateau.%为了解西秦岭北缘-拉脊山两侧的地貌差异及其发育机制,利用DEM数据结合地质数据,提取局部地形起伏并绘制高程带状剖面图,定量化揭示了西秦岭北缘-拉脊山东西两侧地貌结构；在此基础上,统计了两侧新生代不同时期地层砂岩的高程像元众数,并进行了对比分析；通过对已知地质资料的提取和归纳,对比了西秦岭北缘-拉脊山断裂两侧新生代盆地地层岩性及沉积相.结果表明,界限以东新生代地层呈现地层年代越老高程越高的趋势；界限以西则呈现古近纪至新近纪地层越新高程越高、第四纪地层高程最低的特征.这种地层发育规律体现了西秦岭北缘-拉脊山两侧的地貌演化过程存在差异,即东侧水系发育时间早于西侧,地貌接受侵蚀的时间较长.同时,也从侧面反映了东、西两侧构造活动强度与时间的不一致性,古近纪以来东侧构造演化具有自SW向NE逐渐扩展的趋势；而西侧构造演化更为复杂,体现在新生代以来不同断裂带隆升历史的不一致性以及在较强的挤压应力及较弱剥蚀共同作用下的增生过程.