Experimental weathering of a volcaniclastic critical zone profile: Key role of colloidal constituents in aqueous geochemical response
Experimental weathering of a volcaniclastic critical zone profile: Key role of colloidal constituents in aqueous geochemical response
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火山碎屑临界区剖面的实验风化：胶体成分在水地球化学响应中的关键作用
DOI：
10.1016/j.chemgeo.2020.119886
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发表时间：
2021
期刊：
影响因子：
3.9
通讯作者：
Chorover, J.
中科院分区：
文献类型：
--
作者：
Moravec, B.G.;Keifer, V.;Root, R.A.;White, A.M.;Wang, Y.;Olshansky, Y.;McIntosh, J.;Chorover, J.
风化剖面通常是复杂的，从近地表更高度转化的物质（例如，移动的土壤）到风化程度较低的母质（例如，深层多孔基岩）。当剖面的不同深度与侵蚀性大气沃茨水反应时，很难从现场数据中解决材料性质对矿物风化短期速率的影响（即，相对于初级硅酸盐而言是稀的和不饱和的）。在本研究中，我们的目的是测量矿物转化反应的变化，这些反应发生在受控的实验室条件下，作为深度的函数收集样品（例如，地质结构、矿物组合和风化特征的空间分布）。我们进行了一系列的批处理风化实验提取的核心材料从两个钻孔到35米的零级集水区流纹岩Jemez河流域临界区天文台，NM，美国。在与用大气CO2预平衡的水溶液反应时，矿物溶解不限于一个相，而是包括反应的组合，包括（在降低的风化速率下）方解石>沸石>层状硅酸盐>无定形SiO2>长石。矿物转化率取决于矿物组合，结构，和热液蚀变的遗产。结果还表明，现有的和新形成的胶体中的Al，Si和Fe的动员和再分配的重要作用，特别是对材料的证据，以前的热液蚀变。火山角砾岩，这使得顶部14米的西部部分的集水区，主要是由风化的岩屑，其中水溶液化学控制的快速方解石溶解/沉淀反应。热液蚀变凝灰岩，这使得顶部15米以上的大部分集水区，表现出胶体沸石，随后溶解，引起蒙脱石沉淀（无论是在原位和/或沿着流路）的初始分散。溶质签名来自水/岩石的相互作用，在深，热液蚀变泡状凝灰岩相媲美的浅蚀变凝灰岩，但不同的深，未蚀变，火山岩为主的凝灰岩。我们属性的差异，反应表面积易受化学侵蚀的积极沃茨（蚀变岩更大）和原生矿物屏蔽的Fe和Mn氧化物在未蚀变凝灰岩断裂面。这项研究强调了使用提取的岩心实验风化，以帮助解释基于现场的，水化学的方法，可以在其他地质复杂的地形。
Weathering profiles are often complex, extending from more highly transformed materials in the near surface (e.g., mobile soils) to less weathered parent material (e.g., variably porous bedrock) at depth. It is difficult to resolve from field data the impacts of material properties on the short-term rates of mineral weathering when different depths of the profile are reacted with aggressive meteoric waters (i.e., dilute and undersaturated with respect to primary silicates). In the present study, we aimed to measure variation in mineral transformation reactions that occurs under controlled laboratory conditions for samples collected as a function of depth (e.g., spatial distribution of geologic texture, mineral assemblage, and weathering features) across a deep weathering profile in volcaniclastic parent rock. We conducted a series of batch weathering experiments of extracted core materials from two borings to 35 m across a zero-order catchment in the rhyolitic Jemez River Basin Critical Zone Observatory, NM, USA. Upon reaction with aqueous solutions pre-equilibrated with atmospheric CO2, mineral dissolution was not limited to one phase, but included a combination of reactions including (at decreasing weathering rates) calcite > zeolites > phyllosilicates > amorphous SiO2> feldspar. Mineral transformation rates were dependent on the mineral assemblage, texture, and legacy of hydrothermal alteration. Results also indicated an important role of existing and neoformed colloids in Al, Si, and Fe mobilization and redistribution, especially for materials with evidence of previous hydrothermal alteration. Volcanic breccia, which makes up the top 14 m of the western portion of the catchment, was comprised primarily of weathered lithics, where aqueous solution chemistry was controlled by rapid calcite dissolution/precipitation reactions. Hydrothermally altered tuff, which makes up the top 15 m over most of the catchment, exhibited initial dispersion of colloidal zeolites, which subsequently dissolved, giving rise to smectite precipitation (either in-situ and/or along flowpaths). Solute signatures deriving from water/rock interactions in deep, hydrothermally-altered vesicular tuff were comparable to those in shallow altered tuff, but different from those in deep, unaltered, fracture-dominated tuff. We attribute differences to reactive surface area susceptible to chemical attack by aggressive waters (greater in altered rocks) and primary mineral shielding by Fe and Mn oxides on fracture surfaces in unaltered tuff. This study highlights the use of experimental weathering of extracted cores to help interpret field-based, hydrochemistry with an approach that may be employed in other geologically complex terrains.
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DOI：
10.1029/2019jf005189
发表时间：
2020
期刊：
Journal of Geophysical Research: Earth Surface
影响因子：
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