CONTACT METAMORPHISM AND DECARBONATION DURING EMPLACEMENT OF THE CENTRAL ATLANTIC MAGMATIC PROVINCE, FLORIDA

Due to their large volume and short duration of emplacement, Large Igneous Provinces (LIPs) are associated with dramatic changes to the Earth System and relate to at least three, if not all, of the Big Five mass extinctions and many lesser biotic crises (Bond & Sun, 2021). Climate change is induced by the LIP emission of greenhouse gasses to the Earth’s surface creating biotic stress (Ernst et al., 2021).While these gasses are often associated with massive eruption, they are also associated with contact metamorphism of sediments (Yallup et al., 2013; Groke et al., 2009) to high grades that may lead to ~ 100 % devolatilization of the stored carbon (Heimdal et al., 2020, 2021).

In this study, we propose to quantify the net metamorphic carbon flux due to the emplacement of the Central Atlantic Magmatic Province (CAMP) in Florida basement rock. We will use petrographic analysis and isotopic measurements to track the carbon flux throughout the sample suite. Preliminary results are obtained from a core drilled in the North Florida basement (Florida Geological Survey borehole #W1789). The core consists of organic-rich shales intruded by CAMP basaltic sills. We targeted areas near intruded sills and made isotopic measurements of d¹³C_org, total organic carbon (TOC), d¹³C_carb, and % of calcite throughout the core. We find that directly above the sill, d¹³C_carbbecomes lighter and d¹³C_org becomes heavier with an increase in TOC and calcite %. These results indicate transport of carbon from the bottom to the top of the sill and partial isotopic equilibration between calcite and organic carbon. Petrography confirms calcite growth at the top of the sill and provide little evidence for significant carbon release. In addition, we conducted Raman spectroscopy on the carbonaceous matter to constrain the magnitude and duration of the thermal perturbation experienced by the sedimentary strata. We use the relative intensity of the D (1340–1360 cm⁻¹ and additional D2 band at 1610 cm⁻¹ and D3 band at 1500 cm⁻¹ ) and G bands (1580 cm⁻¹⁾ of Raman spectra (Beyssac et. al, 2002, Aoya et. al, 2010). Preliminary results are promising and in agreement with petrographic analyses and isotopic data.