山东鲁山混合岩表面发现第四纪冰川剥蚀的直接证据——颤痕

A Direct Erosion Evidence of Quaternary Glaciation-Chatter Marks Found in Mt.Lushan,Shandong Province,East of China

本文首次报道了在山东鲁山南坡山谷发现混合岩表面的颤痕。颤痕是冰川底部携带的岩石碎块在下伏基岩表面刮凿而形成的一系列弧形裂隙,颤痕的弧形突出方向与冰川运动方向一致,而裂隙也是向下游方向深入基岩内部,其中突出的中间部位裂隙最深,向两端逐渐变浅直至消失。作者探讨了颤痕的形成机理,认为:颤痕相当于主剪切面上的伴生构造——R剪切面,在剖面上看就是一系列雁列式排列的R面,它不仅是冰川在基岩上运动留下的重要证据,而且还能指示冰体的运动方向。除了颤痕之外,在鲁山山麓还分布着大量的冰碛地貌:巨漂砾、冰碛堤等,在鲁山山脊上还见有典型的壶穴、冲刷槽等冰川融水侵蚀标志。这些标志与颤痕一起构成了强大的证据群,揭示了中国东部曾经发育过第四纪冰川的历史。中国东部是否发育过第四纪冰川?地学界已经争论了80多年,而颤痕的发现为进一步肯定中国东部存在第四纪冰川活动提供了最直接的证据。

This paper reports the discovery of chatter marks on the glaciated bedrock in Mt.Lushan,Shandong Province,east of China.Chatter marks are series of small,curved fractures found on glaciated bedrock surfaces,formed by moving rock fragments frozen at the base of glacial ice.A single chatter mark is perpendicular to the moving direction of the overlying ice,and the arcuate fracture is convex downward.The fracture extends deeply into the bedrock at the center of a chatter mark,and becomes shallower gradually toward the two ends.The authors of this paper analyzed the mechanism of chatter marks.We believe that chatter marks are a series of en echelon R-shear fractures on the bedrock surface.Chatter marks are not only the direct evidences of ice moving over the bedrock,and can show the moving direction of the former disappeared glacier.Apart from chatter marks found in Mt.Lushan,there are other related landform evidences,such as,giant erratics,lateral moraines,potholes and scour grooves or troughs,showing the existence of Quaternary glaciation in the east of China.The controversy on the Quaternary glaciation in the east of China has lasted for more than 80 years,and the discovery of chatter marks in Mt.Lushan provides a direct evidence for the existence of Quaternary glaciation in the east of China.