Relating Weathering Fronts for Acid Neutralization and Oxidation to pCO2 and pO2

Research output: Chapter in Book/Report/Conference proceedingChapter

20 Citations (Scopus)

Abstract

As mineral assemblages formed at depth reequilibrate at Earth's surface, reactions with O2 and CO2 are recorded as depletion profiles in regolith. We use models to explore reaction fronts in regolith developed on two lithologies exposed on ridgetops in the Virginia Piedmont (United States). The ratios, R0, of capacities to consume O2:CO2 differ between the Virginia diabase (R0=0.04) and granite (0.02) protoliths. However, the ratios, R, of actual consumption of O2 (by FeO oxidation) versus CO2 (by silicate weathering) recorded by regolith are identical (~0.02). Although soil gases were not measured, we propose that R=~0.02 because the ratio of soil pO2 to pCO2 (=R') equals ~0.02 for both sites. For Fe-rich diabase, however, R'<R0 and CO2 is depleted deeper than O2, allowing ferrous iron to be lost from regolith. In contrast, R'>R0 for Fe-poor granite and O2 is consumed deeper than CO2, causing iron to be retained. In the granite, the volume constraints during oxidation promote fracturing. In turn, fracturing promotes advection and development of thick regolith. Indeed, modern regolith is generally thicker on granites than diabase, as expected if the condition, 0.02<R'<0.04, characterizes many modern soils. Perhaps for ancient atmospheres with pO2/pCO2<~0.02, thick regolith was also not likely.

Original languageEnglish (US)
Title of host publicationTreatise on Geochemistry
Subtitle of host publicationSecond Edition
PublisherElsevier Inc.
Pages327-352
Number of pages26
Volume6
ISBN (Print)9780080983004
DOIs
StatePublished - Nov 1 2013

Fingerprint

acid neutralization
regolith
Weathering
weathering
Soils
oxidation
Oxidation
Acids
diabase
Silicates
Lithology
granite
Surface reactions
Advection
Minerals
Iron
Gases
Earth (planet)
soil gas
piedmont

All Science Journal Classification (ASJC) codes

  • Environmental Science(all)
  • Earth and Planetary Sciences(all)
  • Chemistry(all)

Cite this

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title = "Relating Weathering Fronts for Acid Neutralization and Oxidation to pCO2 and pO2",
abstract = "As mineral assemblages formed at depth reequilibrate at Earth's surface, reactions with O2 and CO2 are recorded as depletion profiles in regolith. We use models to explore reaction fronts in regolith developed on two lithologies exposed on ridgetops in the Virginia Piedmont (United States). The ratios, R0, of capacities to consume O2:CO2 differ between the Virginia diabase (R0=0.04) and granite (0.02) protoliths. However, the ratios, R, of actual consumption of O2 (by FeO oxidation) versus CO2 (by silicate weathering) recorded by regolith are identical (~0.02). Although soil gases were not measured, we propose that R=~0.02 because the ratio of soil pO2 to pCO2 (=R') equals ~0.02 for both sites. For Fe-rich diabase, however, R'<R0 and CO2 is depleted deeper than O2, allowing ferrous iron to be lost from regolith. In contrast, R'>R0 for Fe-poor granite and O2 is consumed deeper than CO2, causing iron to be retained. In the granite, the volume constraints during oxidation promote fracturing. In turn, fracturing promotes advection and development of thick regolith. Indeed, modern regolith is generally thicker on granites than diabase, as expected if the condition, 0.02<R'<0.04, characterizes many modern soils. Perhaps for ancient atmospheres with pO2/pCO2<~0.02, thick regolith was also not likely.",
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Relating Weathering Fronts for Acid Neutralization and Oxidation to pCO2 and pO2. / Brantley, Susan Louise; Lebedeva, Marina Ivanovna; Bazilevskaya, Ekaterina.

Treatise on Geochemistry: Second Edition. Vol. 6 Elsevier Inc., 2013. p. 327-352.

Research output: Chapter in Book/Report/Conference proceedingChapter

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T1 - Relating Weathering Fronts for Acid Neutralization and Oxidation to pCO2 and pO2

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AU - Lebedeva, Marina Ivanovna

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