GEOLOGY AND PETROLOGY OF THE SOUTHERN CONTACT ZONE, MAGNET COVE IGNEOUS COMPLEX, HOT SPRING CO., ARKANSAS

Mid-Cretaceous Magnet Cove Igneous Complex (MCIC) in Hot Spring Co., central Arkansas is considered a sub-volcanic ring-dike complex of the Arkansas alkali-magmatic province. Magmatites are typically silica-poor, alkali-rich and range from jacupirangite, ijolite, nepheline syenites, phonolite to carbonatite. Fresh rock exposures are limited. However, quarrying operations in wall rocks along the southern margin of the MCIC gave unique access to a contact zone of surprising complexity. The geologic map produced (scale 1:2,000) shows garnet-pseudoleucite syenite as the dominant rock type with feldspathoidal syenitic rocks and various dike rocks in the endocontact zone. They are associated with magmatic breccias and variable ‘melt rocks'. Intrusive contact with hornfels of folded Mississippian Stanley Shale is sharp, discordant, and dips 45 degrees S. Lamprophyric, pyroxenitic, and pseudoleucite syenitic dikes occur in the exocontact zone. Hydrothermal alteration and metasomatism are evident throughout the entire contact zone (i.e., pyrite, fluorite, rutile, pseudoleucite, cancrinite).

Results of detailed polarization-microscopic studies, XRD and SEM/EDS examinations, and whole rock chemistry will characterize this unique suite of fresh MCIC rocks.