CONTACT METAMORPHISM AND THE RELEASE OF CARBON AND SULFUR VOLATILES: A STUDY OF THE EFFECTS OF DIABASE EMPLACEMENT
We aim here to better understand how intrusion into organic-rich facies releases volatiles and to quantify the relative contribution of carbonaceous and sulfurous species from each of the magmatic and sedimentary sources. We present geochemical datasets from Triassic lacustrine organic-rich facies within the Culpeper Basin of the Newark Supergroup (Northern Virginia), which experienced Jurassic emplacement of thick diabase sheets of the CAMP. Meta-sediments were regularly sampled along individual beds that run approximately orthogonal to contacts with the diabase, with sampling frequency ranging from the decimeter scale proximal to intrusions to the decameter scale several hundred meters from intrusions. Sulfur content in the sediments increases by approximately a factor of ten over the first five meters from the intrusion, with both carbon (δ13C) and sulfur (δ34S) isotope data showing strong positive excursions from the initial, pre-metamorphic values revealed by distal samples. These results, coupled with petrographic constraints, thermal, and thermodynamic models, illustrate how major and accessory mineral assemblages evolved during contact metamorphism and controlled both the release of sulfur-bearing volatiles and the isotopic fractionation of this sulfur.