Abstract 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.

中文翻译：

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火山碎屑临界带剖面的实验风化：胶体成分在水相地球化学响应中的关键作用

摘要 风化剖面通常是复杂的，从近地表中高度转变的材料（例如，流动土壤）延伸到深度风化程度较低的母体材料（例如，可变多孔基岩）。当剖面的不同深度与侵蚀性大气水（即相对于原生硅酸盐稀释和不饱和）发生反应时，很难从现场数据中解决材料特性对矿物风化的短期速率的影响。在本研究中，我们旨在测量在受控实验室条件下发生的矿物转化反应的变化，这些变化是作为深度的函数（例如，地质结构、矿物组合和风化特征的空间分布）在整个深风化剖面上收集的。火山碎屑母岩。我们在美国新墨西哥州流纹质 Jemez 河流盆地临界区天文台的零级集水区对从两个钻孔到 35 m 处提取的岩心材料进行了一系列批量风化实验。在与用大气 CO2 预平衡的水溶液反应后，矿物溶解不仅限于一个相，还包括反应的组合，包括（以降低的风化速率）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、质地和热液蚀变遗留物。结果还表明，现有的和新形成的胶体在 Al、Si 和 Fe 的动员和重新分布中起着重要作用，尤其是对于具有先前热液蚀变迹象的材料。火山角砾岩，构成集水区西部顶部 14 m 的部分，主要由风化岩屑组成，其中水溶液化学由快速方解石溶解/沉淀反应控制。热液蚀变凝灰岩构成了大部分集水区的顶部 15 m，表现出胶体沸石的初始分散，随后溶解，引起蒙脱石沉淀（原位和/或沿流动路径）。源自深部热液蚀变水泡凝灰岩中的水/岩石相互作用的溶质特征与浅部蚀变凝灰岩中的溶质特征相当，但与深部、未蚀变、以裂缝为主的凝灰岩中的溶质特征不同。我们将差异归因于易受侵蚀性水（蚀变岩石中更大）化学侵蚀的反应表面积和未蚀变凝灰岩断裂表面上铁和锰氧化物对主要矿物的屏蔽。这项研究强调了使用提取的岩心的实验风化来帮助解释基于现场的水化学，其方法可用于其他地质复杂的地形。