INVESTIGATIONS INTO THE ORIGINS OF VOLCANISM AND THE TECTONIC EVOLUTION OF THE SOUTHEASTERN US USING GEOCHEMICAL AND GEOCHRONOLOGICAL METHODS

Southeast Laurentia has many suites of alkalic volcanics with either no known origin or lack of geochronological and geochemical data. The area of interest revolves around the Mississippi Valley Graben (MVG), an area of significant intraplate seismic activity and volcanism throughout geologic history. It is an asymmetric depression caused by extensional tectonics which occurred during the rifting of Pangea following the beginning of the Triassic Period (~255 Ma) resulting in a monoclinal shift in accordance with the regional dip. Within the graben is the Mississippi Embayment (MSE). Trending at ~210°, the MSE is a southward plunging (~3°) trough filled with marine-fluvio-deltaic sedimentary rock of Cretaceous-Paleogene ages topped with Quaternary alluvium that coarsens to the north of the MSE. Throughout the MSE and surrounding region are suites of ultramafic and alkalic intrusives and associated volcanic suites from the Cretaceous (~145-65 Ma), these suites include peridotite, lamprophyre, kimberlite, syenite, and carbonatite. Utilizing a variety of geochemical and geochronological analysis methodologies (bulk, trace, and REE analysis, Rb-Sr, Sr-Sr, Ar-Ar, U-Th-Pb, etc.), this ongoing research project is designed to reveal how North America has moved and evolved, and to provide the insight necessary for reconstructing the southeastern portion of Laurentia throughout geologic time. Geochemical (Trace/REE) and petrologic analyses of preliminary samples indicate a deep mantle origin (≥150 km) for samples from the Crater of Diamonds State Park in Murfreesboro, AR. REE curves indicate magma evolution in the presence of garnet. For samples from Magnet Cove, AR, they indicate similar evolution trends, but are not as profound. The proximity to each other and linearity of these volcanic suites suggest a possibility of an east moving hotspot passing beneath SE Laurentia during the Mesozoic. The strata of the MSE also, have not been downward warped, which generally indicates extensional systems. Further analysis of previous and new data is underway.