Progressive ductile shearing during till accretion within the deforming bed of a palaeo-ice stream
Progressive ductile shearing during till accretion within the deforming bed of a palaeo-ice stream
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古冰流变形床内蒂积积过程中的渐进韧性剪切
DOI：
10.1016/j.quascirev.2018.06.009
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发表时间：
2018
影响因子：
4
通讯作者：
Phillips E
中科院分区：
文献类型：
--
作者：
Phillips E
本文介绍了对波兰 Środa Wielkopolska 以西的 Weichselian（Devensian）Odra 古冰流下方形成的厚冰碴进行详细微观结构研究的结果。这条向东南流动的冰流是众多快速流动的冰走廊之一，这些冰走廊排干了波罗的海地区斯堪的纳维亚冰盖的水。从宏观上看，形成这条冰流床的巨大的、横向广泛的冰碛缺乏任何明显的冰川构造作用（逆冲、褶皱）证据。然而，微观尺度分析表明，河床变形主要由叶理发育主导，记录了水平冰下剪切带内渐进的韧性剪切。已经确定了连续五代碎屑微结构（S1 至 S5），定义了一组冰上和下冰浸 Riedel 剪切，以及与冰床界面共面的次水平剪切叶理。剪切织物之间的横切关系记录了在此渐进剪切事件期间变形样式的时间变化。收银台内的运动学指标（S-C 和 ECC 型织物）表明一致的 SE 方向剪切感，与区域冰流模式一致。提出了一种涉及堆积过程中增量渐进简单剪切的地床变形模型。这种变形的相对年龄是历时的，向上逐渐变年轻，与伴随变形床顶部堆积的冰下剪切作用相一致。微织物相对强度的变化记录了在快速冰流期间施加在耕耘机上的累积应变大小以及冰与底层之间的耦合程度的变化。
This paper presents the results of a detailed microstructural study of a thick till formed beneath the Weichselian (Devensian) Odra palaeo-ice stream, west of Środa Wielkopolska, Poland. This SE-flowing ice stream was one of a number of corridors of faster flowing ice which drained the Scandinavian Ice Sheet in the Baltic region. Macroscopically, the massive, laterally extensive till which formed the bed of this ice stream lacks any obvious evidence of glaciotectonism (thrusting, folding). However, microscale analysis reveals that bed deformation was dominated by foliation development, recording progressive ductile shearing within a subhorizontal subglacial shear zone. Five successive generations of clast microfabric (S1 to S5) have been identified defining a set of up-ice and down-ice dipping Riedel shears, as well as a subhorizontal shear foliation coplanar to the ice-bed interface. Cross-cutting relationships between the shear fabrics record temporal changes in the style of deformation during this progressive shear event. Kinematic indicators (S-C and ECC-type fabrics) within the till indicate a consistent SE-directed shear sense, in agreement with the regional ice flow pattern. A model of bed deformation involving incremental progressive simple shear during till accretion is proposed. The relative age of this deformation was diachronous becoming progressively younger upwards, compatible with subglacial shearing having accompanied till accretion at the top of the deforming bed. Variation in the relative intensity of the microfabrics records changes in the magnitude of the cumulative strain imposed on the till and the degree of coupling between the ice and underlying bed during fast ice flow.
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影响因子：
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DOI：
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影响因子：
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