Identifying a reference frame for calculating mass change during weathering: A review and case study utilizing the C# program assessing element immobility and critical ratio methodology

Carrasco, T.L.; Girty, Gary H.

doi:10.1016/j.catena.2014.10.009

Cited by 15 publications

(3 citation statements)

References 40 publications

(130 reference statements)

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“…Similarly, the first‐order chemical rate law, where d C /d t = kC , integrates to ln C = −kt + ln C 0 , where a plot of ln C as a function of time, t , gives a straight line with a slope of −k . These natural laws of chemistry lead to log‐normal distributions of geochemical species that span many orders of magnitude (Aitchinson, ; Woronow and Love, ; Baumgartner and Olsen, ; Cardenas et al ., ; Schedl, ; Carrasco and Girty, ), to geochemical processes that are proportional to concentrations only when viewed on a log scale, and to the commonly used ‘pX’ notation to refer to the negative common log (base 10) of a chemical concentration or equilibrium constant (e.g. pH, pOH, p K a ).…”

Section: Resultsmentioning

confidence: 99%

Quantifying weathering on variable rocks, an extension of geochemical mass balance: Critical zone and landscape evolution

Fisher

Aufdenkampe

Yoo

2017

Earth Surf Processes Landf

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We present a statistical model of soil and rock weathering in deep profiles to expand the capacity to assess weathering to heterogeneous bedrock types, which are common at the Earth's surface. We developed the Weathering Trends (WT) model by extending the fractional mass change calculation (tau) of the geochemical mass balance model in two important ways. First, WT log transforms the elemental ratio data, to discern the log‐linear patterns that naturally develop from thermodynamic and kinetic laws of chemistry. Second, WT statistically fits log‐transformed element concentration ratio data – log(cj/ci), the only depth‐varying term in tau – as a function of depth to determine characteristic depths of transitions in weathering processes, along with confidence intervals. With no prior assumptions, WT estimates average parent material composition, average composition of the upper weathered zone and mean fractional mass change of each element over the entire weathering profile. WT displays the mean shape of weathering profiles of log‐transformed geochemical data bounded by calculated confidence intervals. We share the WT model code as an open‐source R package (https://github.com/fisherba/WeatheringTrends). The WT model was designed to interpret two 21 m cores from the Laurels Schist bedrock in the Christina River Basin Critical Zone Observatory in the Pennsylvania Piedmont, where our morphological and elemental data provided inconclusive estimates of bedrock depth. The WT model differentiated between rock variability and weathering to delineate the maximum extent of weathering at 12.3 m (CI 95% [9.2, 21.3]) in Ridge Well 1 and 7.2 m (CI 95% [4.3, 13.0]) in Interfluve Well 2. The water table was 5–8 m below fresh rock at Ridge Well 1, but at the same depth as fresh rock at the lower elevation interfluve. We assess statistical approaches to identify the best immobile element for use in WT and tau calculations. Copyright © 2017 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 99%

Quantifying weathering on variable rocks, an extension of geochemical mass balance: Critical zone and landscape evolution

Fisher

Aufdenkampe

Yoo

2017

Earth Surf Processes Landf

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“…Mass-balance calculations have been used for decades to investigate bulk changes in geochemistry between altered and unaltered rock pairs from the same lithology (e.g., Grant 1986; MacLean and Barrett 1993; van Dongen et al 2010; Carrasco and Girty 2015;Uvarova et al 2017). Classical mass balance calculations rely on sample versus sample comparisons, in which the results of two samples (one altered and the other being an unaltered equivalent) are extrapolated as representing entire alteration domains.…”

Section: Mass Transfer Calculation Methodologymentioning

confidence: 99%

The lithogeochemical signatures of hydrothermal alteration in the Waihi epithermal district, New Zealand

Barker

Hood

Hughes

et al. 2019

New Zealand Journal of Geology and Geophysics

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Whole rock lithogeochemical data from the andesite rocks which host lowsulfidation epithermal gold veins in the Waihi district, New Zealand have been used to interpret hydrothermal alteration processes that variably altered the andesite rocks. The andesite host rocks are interpreted to have similar primary chemical compositions throughout the Waihi area, as reflected in similar ratios of immobile elements (e.g. Zr, Ti and other high field strength elements). The geochemical data reveal that elevated K/Al ratios occur in rocks proximal to low-Au-Ag deposits, reflecting adularia alteration in the host rocks associated with the upflowing hydrothermal fluids. Silicification of host rocks is achieved both by the addition of SiO2, as well as the destruction of plagioclase (reflected in the loss of CaO and Na2O). The rocks have been variably altered, with calcite and pyrite abundance reflecting the addition of carbon and sulfur. Pathfinder element (e.g. As, Sb) concentrations are variable across the district, with high pathfinder element concentrations interpreted to reflect proximity to hydrothermal fluid flow. Together, the results provide a district scale overview of hydrothermal alteration at Waihi, and emphasize the utility of lithogeochemistry for classifying and quantifying hydrothermal alteration that can then be used to interpret hydrothermal processes and assist mineral exploration.

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“…), the calculations must also include an appropriate assessment of an immobile element profile. Selection of an immobile element for use in the mass balance model is one where elemental concentrations are statistically indistinguishable from parent rock to weathered rock (Woronow andLove 1990, Schedl 1998;Bern and White, 2011;Carrasco and Girty, 2015). Aluminum, titanium, and zirconium are the most commonly used immobile element factors, although silicon has also been shown to be an effective substitute in certain systems.…”

Section: Mass-balance Comparisonmentioning

confidence: 99%

Evaluating Control of Slope-Aspect on Deep Geochemical Weathering Within the Boulder Creek Critical Zone Observatory

Eldam¹

2016

Geological Society of America Abstracts With Programs

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Geochemical weathering in the Critical Zone is an important source of mobile regolith and solutes that drive landscape evolution and nutrient cycling. An in-depth understanding of geochemical processes is integral to prediction and evaluation of Earth surface response to natural and anthropogenic perturbations such as global climate change and land use. This study evaluates chemical and mineralogical changes from the surface to depths >15 m in the Gordon Gulch watershed of the Boulder Creek Critical Zone Observatory and investigates hillslope aspect control of weathering processes. These data exhibit trends consistent with higher weathering intensity at shallow depths on the south-facing compared to north-facing hillslopes, but deeper overall weathering on north-facing hillslopes. Geologic heterogeneity complicates interpretations of parent material for the weathering profile, and greater constraints are needed to quantitatively evaluate weathering processes in highly heterogeneous bedrock.

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Identifying a reference frame for calculating mass change during weathering: A review and case study utilizing the C# program assessing element immobility and critical ratio methodology

Cited by 15 publications

References 40 publications

Quantifying weathering on variable rocks, an extension of geochemical mass balance: Critical zone and landscape evolution

Quantifying weathering on variable rocks, an extension of geochemical mass balance: Critical zone and landscape evolution

The lithogeochemical signatures of hydrothermal alteration in the Waihi epithermal district, New Zealand

Evaluating Control of Slope-Aspect on Deep Geochemical Weathering Within the Boulder Creek Critical Zone Observatory

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