Preferred slip-band orientations and bending observed in the Dome Concordia (East Antarctica) ice core
Preferred slip-band orientations and bending observed in the Dome Concordia (East Antarctica) ice core
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在圆顶康科迪亚（南极洲东部）冰芯中观察到的首选滑带方向和弯曲
DOI：
10.3189/172756404781814078
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发表时间：
2004
影响因子：
2.9
通讯作者：
S. Kipfstuhl
中科院分区：
文献类型：
--
作者：
S. H. Faria;S. Kipfstuhl
摘要冰穹C（东南极）冰芯上部1300 m的组构分析揭示了c轴向垂直方向的轻微聚集趋势，该趋势随着深度的增加而逐渐增强，c轴在自由表面的初始各向同性取向分布。这种应变诱导的各向异性与圆顶中预期的宏观应力状态相容，即由垂直压缩主导。然而，当人们分析单个微晶（滑移带）的可见滑移层的取向分布时，证据是完全相反的。对取自不同深度（204 - 1291 m）的冰穹C冰芯样品中的滑动带进行直接观察表明，在几乎水平面上有较高的滑动活动，以这种方式，超过60%的检测到的滑动带相对于水平面的倾角<30 °。此外，观测到的滑移活动是不对称的，也就是说，在20 ° C下识别的滑移带的数量通常与在160 ° C下发现的数量不可比较。这些特征与预测的由压缩和/或伸展引起的滑动活动不一致。在这项工作中，我们提出的证据，这种意想不到的取向分布的滑移带，并讨论了一些可能的原因。自然和人工代理人进行了调查，连同他们各自的后果冰盖建模和冰芯处理。此外，我们发现在某些微晶弯曲滑移带的发生。这种弯曲代表了结晶化的早期阶段，并突出了晶体水平上变形的强烈不均匀性。此外，它还表明，地球自转可能在数学上被解释为一个连续的旋转过程，其特征是c轴从一个共同的方向发散。
Abstract Fabric analysis of the upper 1300 m of the Dome C (East Antarctica) ice core reveals a slight clustering tendency of c axes towards the vertical, which gradually enhances with depth from an initially isotropic orientational distribution of c axes at the free surface. Such a strain-induced anisotropy is compatible with the expected macroscale stress state in a dome, i.e. dominated by vertical compression. Yet, when one analyzes the orientational distribution of the visible gliding layers of individual crystallites (slip bands), the evidence is quite contrasting. Direct observation of slip bands in samples from the Dome C ice core taken from different depths (204–1291 m) indicates a higher slip activity in nearly horizontal planes, in such a manner that >60% of the detected slip bands have an inclination of <30˚ with respect to the horizontal. Furthermore, the observed slip activity is not symmetric, i.e. the number of slip bands discerned at 20˚, say, is usually not comparable with the number found at 160˚. Such features are not consistent with the predicted slip activity induced by compression and/or extension. In this work, we present evidence for this unexpected orientational distribution of slip bands and discuss some of the possible causes. Natural and artificial agents are investigated, together with their respective consequences for ice-sheet modeling and ice-core processing. Additionally, we show the occurrence of bent slip bands in certain crystallites. Such a bending represents an early stage of polygonization, and highlights the strong inhomogeneity of deformation at the crystal level. Moreover, it indicates that polygonization might be mathematically interpreted as a continuous process of rotation, characterized by the divergence of c axes from a common direction.