Abstract: The faulted rocks in the Sino-Mongolian Boundary Thrust are uncohesive gouges commenly a few or tens of centimeters in thickness (locally up to 3 meters). Analysis of 13gouge samples show that the content of clay minerals (grain size < 20 µm) are quite variable, ranging from 5 to 44 percent. The main clay minerals are illite and kaolinite; remaining claymaterial is montmorillonite and chlorite. These clay minerals appearas either angular fragments or rounded granulitic grains. Some micro-spheroclasts or microsphaeroidal fragments of clay minerals caused by mechanical grinding are found in the gouge. The illite fragments are not suitable for K-Ar model age determination. The fragments of clay minerals and micro-spheroclasts suggest that the thrusting occurred at least twice. The morphological features on the quartz grains are due to solution; these grains along with euhedral crystals of gypsum and calcite imply that the thrusting is inactive.

Key words: thrust, gouge, micro-spheroclast

摘要： 中蒙边境特大型推覆构造带中的断层泥厚约数厘米至数十厘米，局部厚达3m，是一套未粘结的断层岩。断层带中的13个断层泥样品分析表明，粘土矿物（粒径＜2µm）的含量变化范围较大，约占5%～44%。这些粘土矿物主要是伊利石、高岭石，其次为蒙脱石和绿泥石，呈棱角状碎片和圆化的碎砾。研究发现了微量机械碾磨成因的粘土矿物显微球状砾。碎裂的伊利石不宜用于K-Ar模式年龄测定。碎裂的粘土矿物及显微球状砾说明，所研究的推覆断层可能至少经历两次活动。断层泥中石英碎砾的溶蚀形貌以及自形石膏和方解石晶体表明该断层不是活断层。

关键词: 推覆构造, 断层泥, 显微球状砾