Resolving Deep Critical Zone Architecture in Complex Volcanic Terrain
AuthorMoravec, Bryan G.
White, Alissa M.
Root, Robert A.
Paras, Ben K.
Pelletier, Jon D.
Holbrook, W. Steven
AffiliationUniv Arizona, Dept Hydrol & Atmospher Sci
Univ Arizona, Dept Environm Sci
MetadataShow full item record
PublisherAMER GEOPHYSICAL UNION
CitationMoravec, B. G., White, A. M., Root, R., Sanchez, A., Olshansky, Y., Paras, B. K., et al. (2020). Resolving deep critical zone architecture in complex volcanic terrain. Journal of Geophysical Research: Earth Surface, 125, e2019JF005189. https://doi.org/10.1029/2019JF005189
RightsCopyright © 2020. American Geophysical Union. All Rights Reserved.
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AbstractCritical zone (CZ) structure, including the spatial distribution of minerals, elements, and fluid-filled pores, evolves on geologic time scales resulting from both top-down climatic forcing and bottom-up geologic controls. Climate and lithology may be imprinted in subsurface structure as depth-dependent trends in geophysical, geochemical, mineralogical, and biological datasets. As the weathering profile is as much (or more) a product of past environmental conditions, development of predictive models requires understanding the relative roles of climatic forcing and the geologic template on which CZ processes evolve. Doing so in complex volcanic terrains with high initial bedrock porosity and distinct depositional and hydrothermal alteration histories is particularly challenging. To resolve CZ structure in a rhyolitic catchment in the Valles Caldera National Preserve (NM, USA), this study combined geophysics, drilling, and laboratory analyses to produce depth-resolved porosity, geochemistry, and mineralogy datasets to >40 m in depth. Quantitative X-ray diffraction analysis showed that local mineral transformations control complex chemical enrichment/depletion (tau) patterns. Using linear discriminant analysis, key variables enabled separation of complex-layered geology into discrete zones. Contemporary, matrix-dominated weathering processes and modern hydrologic fluxes occur dominantly within the top 15 m of the weathering profile. This zone is convoluted by incomplete primary mineral weathering and overprinted by post-eruption weathering and metasomatism. Matrix weathering transitions to fracture surface weathering driven by deep percolation of slower moving, longer residence time meteoric waters at depth. By altering initial conditions and weathering trajectory, geologic legacy is a critical factor in how this subsurface landscape evolved and functions.
Note6 month embargo; published online: 21 January 2020
VersionFinal published version