Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 489, Issue -, Pages 123-134Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2018.02.028
Keywords
metamorphic decarbonation; thermodynamic modeling; fluid infiltration; metamorphic carbon flux
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Funding
- National Science Foundation [EAR-9706638, EAR-9810089, EAR-1650329]
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We undertake thermodynamic pseudosection modeling of metacarbonate rocks in the Wepawaug Schist, Connecticut, USA, and examine the implications for CO2 outgassing from collisional orogenic belts. Two broad types of pseudosections are calculated: (1) a fully closed-system model with no fluid infiltration and (2) a fluid-buffered model including an H2O-CO2 fluid of a fixed composition. This fluid-buffered model is used to approximate a system open to infiltration by a water-bearing fluid. In all cases the fully closed-system model fails to reproduce the observed major mineral zones, mineral compositions, reaction temperatures, and fluid compositions. The fluid-infiltrated models, on the other hand, successfully reproduce these observations when the Xco, of the fluid is in the range similar to 0.05 to similar to 0.15. Fluid-infiltrated models predict significant progressive CO2 loss, peaking at 50% decarbonation at amphibolite facies. The closed-system models dramatically underestimate the degree of decarbonation, predicting only 15% CO2 loss at peak conditions, and, remarkably, <1% CO2 loss below similar to 600 degrees C. We propagate the results of fluid-infiltrated pseudosections to determine an areal CO2 flux for the Wepawaug Schist. This yields 10(12) mol CO2 km-(2) Myr(-1), consistent with multiple independent estimates of the metamorphic CO2 flux, and comparable in magnitude to fluxes from mid-ocean ridges and volcanic arcs. Extrapolating to the area of the Acadian orogenic belt, we suggest that metamorphic CO2 degassing is a plausible driver of global warming, sea level rise, and, perhaps, extinction in the mid-to late-Devonian. (C) 2018 Elsevier B.V. All rights reserved.
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