Recumbent folding of divide arches in response to unsteady ice-divide migration
Recumbent folding of divide arches in response to unsteady ice-divide migration
复制标题
分水岭斜向折叠响应不稳定的冰分水岭迁移
DOI：
10.3189/172756505781829412
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发表时间：
2005
影响因子：
3.4
通讯作者：
E. Waddington
中科院分区：
文献类型：
--
作者：
H. Jacobson;E. Waddington
摘要在流分水岭（雷蒙德隆起）正下方的地层中的拱是由稳定冰盖流模型预测的，并已在几个冰穹中观察到。在这里，我们模拟这些层的演变时，一个以前固定的鸿沟迅速迁移到一个新的位置，然后再次成为固定的，离开在侧翼位置的拱形层。当它们被水流带到下游时，这些废弃的拱门可以发展成横卧褶皱。这些褶皱可以在很宽的分水岭迁移速度范围内发生。产生这些横卧褶皱的剪切流也将褶皱层分布在原始分水岭位置下游的一个很宽的距离上。如果分水岭偏移是突然的，“预岩心”或包括岩心相对等时线的物质线可用于快速识别废弃雷蒙德隆起的部分，这些部分将在下游任何未来的冰芯地点被推翻。如果像格陵兰岛的情况一样，分水岭永远不会稳定到足以产生成熟的拱，那么这种类型的褶皱就不会发生。最有可能发现这种褶皱的地方可能是被不稳定的冰流包围的冰脊的侧面。
Abstract Arches in stratigraphic layers directly under a flow divide (Raymond bumps) are predicted by models of steady ice-sheet flow, and have been observed in several ice domes. Here, we model the evolution of these layers when a formerly stationary divide migrates rapidly to a new position, then again becomes stationary, leaving the arched layers in a flank position. As they are then carried downstream with the flow, these abandoned arches can develop into recumbent folds. These folds can occur over a wide range of divide migration speeds. The shearing flow that produces these recumbent folds also distributes the folded layers over a wide distance downstream from the original divide location. If the divide offset is abrupt, ‘pre-cores’, or material lines comprising core-relative isochrones, can be used to quickly identify portions of an abandoned Raymond bump that would be overturned at any future ice-core site downstream. If, as appears to be the case in Greenland, the divide is never stable long enough to produce a mature arch, folds of this type would not occur. The most likely place to find such folds might be the flank of an ice ridge bounded by unsteady ice streams.