Subaerial salt extrusions in Iran as analogues of ice sheets, streams and glaciers
Subaerial salt extrusions in Iran as analogues of ice sheets, streams and glaciers
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DOI：
10.1016/j.earscirev.2009.09.004
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发表时间：
2009-12
影响因子：
12.1
通讯作者：
C. Talbot;V. Pohjola
中科院分区：
文献类型：
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作者：
C. Talbot;V. Pohjola
冰（H2O）和盐（岩盐，氯化钠）有许多共同的物理性质，在手标本和陆上重力驱动的流动彼此相似。然而，虽然大多数重要的冰体在寒冷的高地积累，并在它们形成后不久在重力作用下扩散，但大多数重要的盐体积累在热带海洋盆地，并且在它们流动之前必须被超过1公里的其他岩石掩埋。埋藏的盐通过差异载荷被驱动到称为底辟的各种刺穿结构中。许多底辟以异地盐片的形式突出到地表。过去25年来，全球超过35个盆地中已解释了数千片外来盐，主要位于被动大陆边缘的趾部和造山带，其中一些面积> 103平方公里。大多数以前的盐层现在都在海底或地下，但在伊朗有几个活跃的例子暴露在美丽的地方。在它们被引入西方科学后不久，这些被与冰冰川进行了比较，这种比较一直被忽视。在这里，我们更新了这个类比，并使用现代对流动冰和盐的理解来研究可能对两个研究领域以及外星科学家都有利的相似性和差异。冰和盐的流动体的剖面、内部结构和组构是其供应和损失预算历史的敏感尺度。然而，雪只是在堆积的地方压实，而盐层则是由已经变形的盐从下面补充的。当盐底辟第一次出现在陆地上时，它们挤压出圆顶，这些圆顶成熟为粘性喷泉的轮廓，这些喷泉经常为被称为纳马基的冰川状流动提供水源。在局部耗尽其深层源层后，盐泉扩散到冰盖正常的粘性液滴轮廓。冰通常在其绝对熔化温度的>80%（通常>90%）时变形，而大多数盐在其同源温度的<50%时变形;因此，盐中的颗粒形状织物比冰中更清晰，并且具有更长的应变记忆。变形盐图流线中的叶理有助于了解内部褶皱的发育。盐层很少像流动的冰一样侵蚀它们的通道，内部的碎片积累在它们的顶部而不是底部。冰盖漂浮在水面上，但由于作为盐的密度是冰的两倍，所以福尔斯落在纳马基尔表面上的雨水往往会停留在那里。冰川和纳玛基耶河都有涌浪，但纳玛基耶河的涌浪和边界条件变化之间的联系比冰川要清楚得多。由于陆地冰向海洋的输送速率是海平面的重要控制因素，我们最后考虑了盐量激增的影响如何与最近的冰川学发现相融合，这些发现涉及边界条件而不是基底的变化。
Ice (H20) and salt (halite, NaCl) share many physical properties and resemble each other in hand specimens and subaerial gravity-driven flows. However, while most significant bodies of ice accumulate in cold highlands and gravity-spread where and soon after they form, most significant bodies of salt accumulate in tropical marine basins and have to be buried by >1km of other rocks before they flow. Buried salt is driven by differential loading into various categories of piercing structures known as diapirs. Many diapirs extrude onto the surface as sheets of allochthonous (out of place) salt. Thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25years, mainly in the toes of passive continental margins and in orogenic belts where some are >103km2in area. Most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in Iran. These were compared to ice glaciers soon after they were introduced to western science, a comparison that has been neglected since. Here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists. The profiles, internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss. However, whereas snow merely compacts where it accumulates, salt sheets are fed from below by already deformed salt. When salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier-like flows known as namakiers. After locally exhausting their deep source layers, salt fountains spread to the profiles of viscous droplets normal for ice caps. Ice typically deforms at >80% (usually >90%) of its absolute melting temperature while most salt deforms at <50% of its homologous temperature; as a result, grain shape fabrics in salt are clearer and have longer strain memories than in ice. Foliations in deformed salt map streamlines aid in the understanding of how internal folds develop. Salt sheets seldom erode their channels like flowing ice and internal debris accumulates on their tops rather than their bases. An ice sheet floats on water but as salt is twice the density of ice; rain that falls onto the top surface of namakiers tends to stay there. Both glaciers and namakiers surge but the association between surges and changes in boundary conditions are much clearer for namakiers than glaciers. Because the rate of delivery of land ice to the oceans is such an important control on sea level, we end by considering how the implications of surging salt converge on recent glaciological findings about changes in boundary conditions other than their bases.