Predicting Rates of Weathering Rind Formation
Predicting Rates of Weathering Rind Formation
复制标题
预测风化皮形成速率
DOI：
10.2136/vzj2014.09.0123
复制
发表时间：
2015
影响因子：
2.8
通讯作者：
A. Hunt
中科院分区：
文献类型：
--
作者：
A. Hunt
基于渗流理论概念的非高斯输运理论在这里应用于地表和近地表碎屑上风化皮的发展。在这个理论中，溶质通过非均质介质的输送与流体流动的行为截然不同。特别是，尽管溶质传输速度和流体速度在单个孔隙的尺度上是相同的，但随着传输距离的增加，溶质速度近似按幂律减小。因此，溶质传输距离 x 作为传输时间 t 的次线性幂 q 增加，q 的预测值介于 0.5 和 1.0 之间。溶质迁移距离随时间变化的已知行为与观察到的风化皮厚度随时间变化的行为相同。 q 的值取决于饱和条件和流动的尺寸限制。例如，裂缝将流动限制在二维表面。在自然界中都发现了二维和三维值。然而，几乎所有风化皮研究分析的 q 值都与不饱和条件一致。三个例外之一是海底玄武岩的情况，它产生的 q 值与饱和条件一致，正如预期的那样。然而，亚基马河谷和特拉基河谷风化壳的情况却不太容易解释，其中 q 值也表明饱和条件。另一方面，分析的四项高山果皮研究以及来自文献的其他三项研究均与不饱和条件和流动限制于二维一致。微裂缝可以引导高山环境中沿二维表面的流动。其他作者引用了高山环境中表面碎屑发生霜冻破碎的情况。当根据给定岩石类型和重力流的水力传导率的几何平均值指定流体流速时，发现外皮厚度的对比通常与总溶质传输距离的对比一致。然而，在高山条件下，果皮的发育可能比预期的要慢。
A theory for non‐Gaussian transport, based on concepts from percolation theory, is applied here to the development of weathering rinds on surface and near surface clasts. In this theory, solute transport through heterogeneous media behaves distinctly from the fluid flow. In particular, although the solute transport velocity and fluid velocities are identical at the scale of a single pore, as transport distances increase, the solute velocity diminishes approximately as a power law. Solute transport distances, x, thus increase as a sublinear power, q, of the transport time, t, with predicted values of q intermediate between 0.5 and 1.0. The known behavior of the solute transport distance as a function of time turns out to be identical to the observed thickness of weathering rinds as a function of time. The value of q depends on conditions of saturation and dimensional constraints to flow. Fractures, for example, constrain flow to two‐dimensional surfaces. Both two‐ and three‐dimensional values were found in nature. However, nearly all the weathering rind studies analyzed yielded values of q consistent with unsaturated conditions. One of three exceptions was the case of submarine basalts, which yielded a q value consistent with saturated conditions, as expected. The cases of the Yakima and Truckee River valley weathering rinds, however, where the values of q also indicated saturated conditions, were less easily explained. On the other hand, four Alpine rind studies analyzed, as well as three others derived from the literature, were all consistent with unsaturated conditions and flow constrained to two dimensions. Microfractures could guide flow along two‐dimensional surfaces in Alpine environments. Occurrence of frost shattering of surface clasts in Alpine environments has been cited by other authors. Contrasts in rind thicknesses were found to be generally compatible with contrasts in total solute transport distances when fluid flow velocities were assigned based on geometric mean values of the hydraulic conductivity for a given rock type and gravity flow. However, rind development under Alpine conditions may be slower than expected.