大兴安岭冰帽群的发现及初步研究

Discovery and Preliminary Study of the Ice Cap in the Da Hinggan Mountains

对于大兴安岭地区是否发生过第四纪冰川作用,地质学界一直存在争议。通过野外调查发现,在内蒙古克什克腾旗世界地质公园青山园区的山脊与山坡上,大规模分布有流线构造,同时在边缘地带存在着典型的终碛条带构造、冰碛砾石扇构造。流线构造由粗粒黑云二长花岗岩组成,砾石为棱角状,多长条形,长为数十厘米至数米。构成流线构造的砾石垄,垄宽1~3 m,高0.3~1.0 m,长数十米,最长的可达数百米。长条状砾石a轴与流线构造的延伸方向一致,板状砾石则叠压成鱼骨状。经与国外文献中冰帽遗迹特征进行对比分析,确定这些流线构造属于冰帽冰碛流线构造,从而证实了大兴安岭地区曾经存在众多小型冰帽,统称为“兴安冰帽群”。根据砾石表面具有极其微弱的风化程度、流线构造与全新世灰黑色亚黏土堆积在一起的特征,初步推断该期冰帽的发生时间可能为全新世的拦马冰期。

There has been a controversy about whether Quaternary glaciation occurred in Da Hinggan Mountains.According to the field investigation,there are streamlines and typical terminal moraine banded structures and moraine gravel fan structures on the edge widely distributed on the ridges and slopes of Qingshan park,Keshiketeng Banner global geopark,Inner Mongolia.The streamline structures are composed of coarse-grained biotite adamellite,and that the gravels are angular and long which ranges from tens of centimeters to several meters and some even reaches several meters.Gravel ridges forming streamline structures are 1~3 m wide,0.3~1.0 m high,tens of meters long,and that the longest one can reach hundreds of meters.The a axis of the long strip gravel is in line with the extension direction of the streamline structure,while the plate gravels are superimposed into herringbones.Through comparative analysis of foreign literatures about the characteristics of ice cap relics,it is determined that these typical streamlines belong to the ice cap moraine streamlines,thus confirming the existence of numerous small ice caps in the Da Hinggan Mountains,which collectively knows as"Xing′an ice cap group".Based on the characteristics of extremely weak weathering degree on the gravel surface,the streamline structure and the accumulation of Holocene gray and black mild clay,it is preliminarily inferred that the occurrence time of this ice cap may be the"Lanma Ice Age"in Holocene.