白利雅盆地构造地貌解析及鲜水河断裂北西段水平滑移速率

白利雅盆地位于青藏高原东部,鲜水河断裂带北西段炉霍活断层与达曲活断层的斜接部位。通过野外实际考查,结合Google Earth地图发现白利雅盆地发育一系列的构造地貌:断层三角面、坡中槽、断错阶地、废弃河道、裂陷湖和阶地面变形。盆地发育的4级阶地是构造成因。废弃河道是新的断裂活动形成的新冲沟、新河道——达曲,其快速下切,废弃老河道,形成狭长的‘U’型沟谷。鲜水河断裂的北西段炉霍活断层切过T3河流阶地,说明其(白利雅以北)是在大约14.92kaB.P.以后形成的,可能预示着构造应力场的变化和白利雅盆地形成。对盆地4级阶地(T1,T2,T3和T4)的河流沉积物光释光(OSL)测年结果分别是 1.06±0.06kaB.P.,1.83±0.06kaB.P.,14.92±0.76kaB.P.和 42.48±2.35kaB.P.,代表了相应阶地的沉积年龄。这些结果与阶地前缘陡坎断错的距离计算显示,从42.48kaB.P.和14.92kaB.P.以来,断层走向平均移动速率分别为3.73mm/a和0.85mm/a,显示从中更新世晚期以来,鲜水河断裂带炉霍活断层水平滑移有减慢的趋势。在42.48~14.92kaB.P.,14.92~1.83kaB.P.和1.83~1.06kaB.P.,相邻阶地垂向隆升或河流下切的速率分别为0.14mm/a(T4~T3),4.66mm/a(T3~T2)和5.19mm/a(T2~T1),显示从中更新世晚期以来,阶地垂直隆升或河流下切有加快的趋势。

STRUCTURAL LANDFORM ANALYSIS IN BAILIYA BASIN AND STRIKE-SLIP VELOCITY IN WEST-NORTH SECTION OF XIANSHUIHE ACTIVE FAULT ZONE

Bailiya Basin is located in west-north segment of Xianshuihe active fault zone,east Tibet Plateau.Working in the field and utilizing Google Earth map,this paper describes a series of structural landform: trough on slope,offset streams,offset of terrace,triangular facet,deformed terrace surface,abandoned river,rift lake.T4 is cut off by Luhe active fault; Kerilong river goes through T3(14.92kaB.P.),and approximately flows along Luohe active fault.This probably means that the tectonic stress field has been changed,Bailiya Basin is formed.Ages by OSL dating(T1,T2,T3 and T4)are followed: 1.06±0.06kaB.P.,1.83±0.06kaB.P.,14.92±0.76kaB.P.and 42.48±2.35kaB.P.,these times perhaps are when the terraces were formed.Since 42.48 and 14.92kaB.P.,the Luhe active fault sinistral strike-slip velocities decreased from 3.73mm/a(42.48kaB.P.~now)to 0.85mm/a(14.92kaB.P.~now); The rates perhaps show that the fault level slip velocities decreased from Late Pleistocene(Q3: 42.48ka)to now.The Daqu(River)incision rates increased from T4~T3(42.48~14.92kaB.P.,0.14mm/a)to T3~T2(14.92~1.83kaB.P.,4.66mm/a)and T2~T1(1.83~1.06kaB.P.,5.19mm/a); These illustrate that terrace incision rates speed up from Late Pleistocene(Q3: 42.48ka)to now.