The contribution to exogenic CO2 by contact metamorphism at continental arcs: A coupled model of fluid flux and metamorphic decarbonation

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2019
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Abstract
Recent work has suggested a possible temporal coincidence between greenhouse intervals and enhanced arc volcanism, motivating the hypothesis that magmatic and metamorphic CO2 emissions from volcanic arcs, particularly those intersecting crustal carbonates, may play a strong role in modulating the long-term carbon budget of the exogenic system. When hot fluid exsolving from arc magmas interacts with carbonate sequences on active margins, contact metamorphism releases CO2 to metasomatic fluids that transport carbon to shallow reservoirs. To estimate the magnitude of CO2 release, here we model how the infiltration of silica-saturated magmatic water into a porous medium facilitates the decarbonation reaction in contact aureoles. Analytical scalings and numerical simulations show that the propagation rate of the reaction front scales with the ratio of the infiltration flux to the mass of the rate-limiting reactant, and accordingly the CO2 flux increases linearly with the infiltration flux. This simple relationship allows for scaling to predict regional and global scale CO2 release at continental arcs if magma emplacement rate is known. Using the global rate of continental arc magma emplacement, we estimate that the present-day contact-metamorphic CO2 release range from ∼0.06 to 0.9 Tmol/yr, half-to-one orders of magnitude smaller than the field-based estimates of carbon output in modern arcs (1.5–3.5 Tmol/yr). Yet, the extrapolated CO2 release from Cretaceous continental arcs via simple infiltration-induced decarbonation is comparable to the release from mid-ocean ridges. CO2 released from continental arcs amplifies the background flux of CO2 from direct degassing of the magma, and therefore may have been key in causing the climatic greenhouse interval in the Cretaceous when there was heightened arc activity. Thus, our result supports the hypothesis that global arc flare-ups at continental margins effectively increase CO2 outgassing coinciding with green-house intervals in the geological past. The contribution by arcs to the tectonic CO2 input could be significant, which needs field-based studies to revise long-term climate models.
Reference Key
openalex_W2987252911 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Xu Chu, Cin‐Ty A. Lee, Rajdeep Dasgupta, Wenrong Cao
Journal american journal of science
Year 2019
DOI
10.2475/08.2019.01
URL
https://doi.org/10.2475/08.2019.01
Keywords Keywords not found

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