【摘要】 云南建水-蒙自一带位于川滇菱形块体向SE145°平移的前锋,受其影响,该地区的蒙自东山断裂、田山断裂和黑泥地断裂等表现出一定程度的晚第四纪活动性,跨过断裂的冲沟被走滑断错。攀枝花以东的蒙自东山断裂右旋错断冲沟和其间的山脊约40m,并在山前洪积扇上形成偏离上游约30m的废弃古河道,古河道中堆积物的年龄为44kaBP,断裂右旋滑动速率约为0.7mma。大红地北一条冲沟在跨过田山断裂时发生右旋拐弯。冲沟在山前形成了年龄分别为31kaBP和39kaBP的2级洪积阶地,呈现出年轻阶地位错量大于老阶地的反常现象。田山断裂的平均右旋滑动速率约0.9mma。发育于黑泥地断裂南侧的多条冲沟在流过断裂时发生一致性的右旋位错,其中一条冲沟位错量达14m,断裂的右旋滑动速率为0.4mma。这一地区自30～40kaBP开始发生了一次明显的构造运动,表现为这一时代的洪积扇上的地貌过程由加积转变为切割,并被断裂错断。断裂的走滑速率明显低于小江断裂带、曲江断裂带和石屏-建水断裂带等。川滇菱形地块向SSE方向的平移及其构造活动不仅仅局限在小江断裂带以西的地块内部,而是引起了外围地块上的断裂活动,但断裂活动强度不及内部断裂的13。冲沟对走滑断错的响应分为3种类型,分别为同步弯曲型、加剧弯曲型和不对称谷地型,其中加剧弯曲型的地貌过程较为复杂。每种类型都记录了断裂的走滑活动,在估算断错量和滑动速率时应甄别不同的响应类型,以免人为的“加大”或“减小”甚至“忽略”断裂的活动幅度。更多还原

【Abstract】 The Jianshui-Mengzi region,where active faults are the Mengzi Dongshan,Tianshan and Heinidi faults,is immediately adjacent to the southeast end of the Sichuan-Yunnan rhombus block.These faults are active in the Late Quaternary and typical faulted gullies are developed.\;Near the Panzhihua village,a few gullies and the crests between them are dextrally offset by the Mengzidongshan fault with a displacement of 40～50m,other gullies are incised 10m in depth in piedmont alluvial fans.The dextral slip rate of the fault is about 0.7mm/a estimated from an abandoned channel dated 44ka BP.North to the Dahongdi village,a gully,forming two alluvial terraces dated 39ka BP and 31ka BP on the piedmont zone,is dextrally displaced by the Tianshan fault.The front edges of the lower and the higher terraces are 75m and 30m away from the original upper reach,respectively,anomalous that the displacement of the younger terrace is longer than that of the older.The mean dextral slip rate of the Tianshan fault is 0.9mm/a.Many gullies are concordantly dextrally offset on the Heinidi fault with displacements of more than 10m.There is a gully south to the Heinidi village incised 4～5m in its ancient fan dated 43ka BP.The gully is dextrally offset 14m with an ‘eyebrow facet’ on the fault.The slip rate of Heinidi fault is estimated as 0.4mm/a.The above data demonstrate that there occurred a tectonic motion since 30～40ka BP,characterized by the incision on and the displacement of the piedmont fans dated 30～40ka BP,the dextral slip rates are 0.4～0.9mm/a,lower than those of the Xiaojiang,Qujiang and Shiping-Jianshui faults.This indicates that the faulting is mainly caused by the pushing of the Sichuan-Yunnan rhombus block.\;The offset gullies existing in the Jianshui-Mengzi region can be divided into 3 types,which are concordant bend,enlarged bend and asymmetric valley,each recording laterally faulting.They need careful discrimination to estimate faulting magnitude and slip rate to avoid artificially “increasing”,“decreasing” or even “neglecting” the faulting.更多还原