摘要
冰流是指冰盖中快速流动(高达10 km/a)的区域。冰流通常长达1000 km,宽200 km,嵌入在冰盖中。沿其流动方向形成了低幅度波纹状基岩床。这些波纹状基岩床由一些高度拉伸的沿着流向呈平行状分布的脊和沟槽(巨型冰川线理)组成。这些巨型冰川线理在空间上继承自体积大、拉伸程度低的鼓丘。由于鼓丘核部的地质条件复杂多变且不存在特征性的岩相,同时很难直接观察到现代冰盖下鼓丘的形成,因而鼓丘的起源在世界上仍然是未解之谜。基于新的高分辨率(0.5 m)LiDAR数据绘制的地形图和对更新世古冰流岩床进行野外地质考察表明,鼓丘和巨型冰川线理是底形连续体(后者由前者演化而来)。它们由基岩或部分岩石和早期较老的沉积物组成,基于此部分学者提出了鼓丘的侵蚀起源说。本文重点介绍了类似鼓丘和巨型冰川线理的椭圆-流线型和带有沟槽的表面,这些表面广泛形成于多种非冰川的地质环境中(无论是在地球上还是在火星上),它们是由于受限剪切作用下颗粒状碎屑对基底面的磨损所产生的。变质核杂岩中的大型滑脱断层和俯冲带巨型逆冲断层的表面显示出槽状表面,其形状和规模能够与巨型冰川线理相类比。多尺度的断层面上都表现出了逐渐消除的类似鼓丘状的"椭圆形凸起",形成带凹槽的岩石光滑面,从而减少了阻力并允许继续滑动。现代冰流岩床记录的冰下地震的独特"纹理"与凹槽内基底面遭受的局部侵蚀和剪切一致,冰下地貌特征加强了与断层运动学的联系。火山碎屑流、陨石撞击坑周围的溅射毯以及滑坡和块体搬运沉积体系的滑动,它们的下垫面都会形成类似巨型冰川线理的沟槽。在人造和生物材料的摩擦接触表面上,也可以重现这些由粒状"磨损碎屑"(被定义为"第三层")切割形成的类似鼓丘的椭圆形凸起和类似巨型冰川线理的沟槽表面。因此,我们提议将鼓丘和巨型冰川线理作为冰川动力学研究的相关组成部分,可以称之为"磨损痕迹"或者"流向剪切痕"。它们是由于不同的冰流速度拖曳粗颗粒的变形冰碛物切割底面(沉积物或者岩石(或其他岩相组合))形成的。地学界颇具争议的鼓丘-冰川线理成因谜团已逐渐清晰。
Ice streams are fast-flowing(up to 10 km/a)arterial corridors as much as 1000 km long and 200 km wide,inset within ice sheets that leave low relief longitudinally-corrugated beds consisting of highly-elongated flow-parallel ridges and grooves(megascale glacial lineations).These are spatially and genetically related to larger less elongate drumlins whose origin(s)remain enigmatic despite more than 150 years of investigation.This uncertainty is largely because of the wide variability of the geology of their cores and the difficulties of observing their formation below modern ice sheets.New high resolution(0.5 m)LiDAR-based mapping and geological studies of the well-exposed beds of Pleistocene paleo ice streams shows that drumlins and megascale glacial lineations are a bedform continuum composed entirely of bedrock,or partial rock and older antecedent sediment favouring an erosional origin proposed by many workers.Here we highlight analogous elliptically-streamlined and grooved surfaces produced by abrasion of substrates below granular debris undergoing confined shear in a wide range of non-glacial geologic settings,both here on Earth and on Mars.Large detachment faults in metamorphic core complexes and the surfaces of subduction zone megathrusts show grooved surfaces that are directly analogous in form and scale to megascale glacial lineations.3-D profiling of fault traces below gouge show progressive elimination of drumlin-like‘elliptical bumps’to form grooved slicken sided surfaces that reduce drag and allow continued slip.Distinct‘streaking’of subglacial earthquakes recorded below modern ice streams is consistent with localized erosion and shear of substrate materials within grooves strengthening the link to fault kinematics.More widely,the basal surfaces of ejecta blankets surrounding meteorite impact craters,pyroclastic flows from volcanoes and at the base of landslides and mass transport deposits are also grooved as a result of erosion below basal granular debris that segregates into distinct longitudinal‘sub-streams’.Elliptical bumps and grooved surfaces cut by granular‘wear debris’(defined as a‘third layer’)are also seen on the surfaces of man-made and biological materials in frictional contact.Correspondingly,we propose that drumlins and megascale glacial lineations are kinematically related components of a glaciodynamic hierarchy of what can be called‘wear tracks’or‘longitudinal shear marks’cut at different ice velocities by coarse-grained deforming till(a subglacial‘third layer’)being dragged over the substrate,whether composed of sediment,or rock(or any combination).The drumlin-MSGL enigma that has been the focus of more than 150 years of research is now closer to being resolved.
作者
周维维
Nick EYLES
Shane SOOKHAN
Niko PUTKINEN
ZHOU Weiwei;Nick EYLES;Shane SOOKHAN;Niko PUTKINEN(Kunming University of Science and Technology,Faculty of Land Resources Engineering,Kunming,Yunnan 650093,China;University of Toronto at Scarborough,Department of Physical and Environmental Sciences,Scarborough ON M1C1A4;Geological Survey of Finland,PO Box 97,FI-67101,Kokkola,Finland)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2021年第8期2306-2317,共12页
Acta Geologica Sinica
基金
云南省应用基础研究基金项目(编号241120200020)
加拿大自然科学和工程研究委员会联合资助成果。
关键词
鼓丘
巨型冰川线理
流线型沟槽
侵蚀起源
摩擦磨损
冰川摩擦学
drumlins
megascale glacial lineations
streamlined grooved
erosional origin
friction and wear
glaciotribology
