辽西晚三叠世末—中侏罗世崩塌-滑坡-泥石流沉积及其构造意义

The Slidding-Slump-Mudflow Sedimentation during the Late Late-Triassic to Middle Jurassic in Western Liaoning Province, China

燕山板内造山带东部辽西、冀北地区,晚三叠世末—中侏罗世期间发生了两次大规模的滑坡、泥石流沉积和成群的巨大岩块崩塌事件。辽西晚三叠世—早侏罗世邓杖子组是一套以碳酸盐岩砾岩为主的崩塌、泥石流、滑坡及深水浊积岩序列,邓杖子组中砾岩的砾石成分自下而上表现出明显的变化规律,即邓杖子组下部砾岩砾石时代新而上部砾岩砾石时代老。其中最新的砾石成分是来自于邓杖子组之下的晚三叠世水泉沟组的安山岩,砾石时代的倒序显示同构造剥蚀-沉积的特点。同时,邓杖子组沉积组合也反映出伸展盆地的沉积特点。邓杖子组沉积后不久,在辽西—冀北的其他地区,还发育许多早—中侏罗世巨大的崩塌岩块,野外见到的最大岩块延伸长度超过4km。崩塌、滑坡、泥石流及成群发育的巨大崩塌岩块都是在地壳快速隆升过程中发生的同构造沉积记录,这从构造-沉积学的角度显示燕山地区在早中生代曾经发生过强烈快速隆升。

During the late Late Triassic to middle Jurassic there occurred two times of a large number of slump,sedimentation of mudflow, and sliding event of huge blocks in western Liaoning province and northern Hebei province of Yanshan intraplate orogen in China. The Late Triassic to Early Jurassic Dengzhangzi formation is a sedimentary sequence of sliding, mudflow, slumping, deepwater turbdite mainly composed of carbonatite conglomerates. The ages of gravels of conglomerates in Dengzhangzi formation become elder from bottom to top. The newest gravels are andesites from the Late Triassic Shuiquangou formation under the Dengzhangzi formation. The upside sequences of the gravels in their ages shows the syn-tectonic erosion or uproofing and sedimentation and the sedimentary facies of Dengzhangzi formation show the sedimentary features of an extensional basin. We also find there are many huge sliding blocks formed after the sedimentation of Dengzhangzi formation, the largest one of the blocks is exceeded 4 km in length, in the other areas of northern Hebei province and western Liaoning province. Generally, the sliding, slumping, mudflow, and a group of huge sliding blocks are the sedimentary records in the rapid uplifting of crust. So occurrence of the sedimentary events shows, in tectono-sedimentation, that the Yanshan area ware rapidly uplifted in the early Jurassic.