10-1 Effect of Depth on Metamorphic Decarbonation in the Sierra Nevada Batholith: Isotopic Analysis of Carbon and Oxygen

Session: Undergraduate and Graduate Geoscience Student Showcase (Posters)

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Abstract:

CO₂ degassing in metamorphic environments is shown to be a significant input flux in the global carbon cycle, having critical environmental implications and perturbing Earth’s climate (Stewart et al, 2019). The Sierra Nevada batholith is a compelling area to study as the existing calcareous rocks underwent contact metamorphism in its expansive region (Kerrick, 1970). While we know that metamorphism releases CO₂, it remains unconstrained if and how the amount of CO₂ released depends on the depth of metamorphism. In the southern part of the Sierra Nevada batholith, different depths of igneous emplacement (from >8 kbar to 3 kbar according to Nadin and Saleeby, 2008) are exposed at the surface. This makes the Sierra Nevada batholith an ideal place to study the effects of depth on CO₂ release. 

We aim to test the hypothesis that as rocks undergo metamorphism at greater depths, the amount of CO₂ degassed is smaller, as more of the CO₂ is trapped. Through analysis by mass spectrometry at the National High Magnetic Field Laboratory and geochemical techniques, we will report the d¹³C and d¹⁸O isotope values across a range of samples from different depths (3 kbar to >8 kbar). We will then compare the isotope values between samples and literature values, interpreting that samples with higher positive isotope values degassed less CO₂ and/or experienced less interaction with magmatic fluid. We hypothesize that the samples that underwent metamorphism at deeper depths (>8 kbar) will record higher positive isotope values than those that underwent metamorphism at shallower depths (3-5 kbar).

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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