BASALTIC MAGMATISM ASSOCIATED WITH TWO SUPERCONTINENT DISPERSALS IN THE CENTRAL APPALACHIAN OROGEN: MODELING SOURCES THROUGH TIME

The breakup of supercontinents is often accompanied by magmatism associated with many possible geodynamic interactions between the mantle and the overlying continental lithosphere. In the central Appalachian orogen, a globally unique geologic setting is available for comparing the magmatic record associated with two supercontinent dispersals: a late Proterozoic event marking the dispersal of supercontinent Rodinia followed by a Mesozoic breakout of Supercontinent Pangaea leading to the present day Atlantic Ocean basin. Spatially overlapping basaltic rocks associated with the two events provide an opportunity to identify common geodynamic mechanisms associated with such events. Using the Mesozoic to recent basalts as time markers we suggest that the sources of the basalts are linked to three recognizable stages of extension. Stage I basalt generation is associated with incipient supercontinent extension with its geochemical/isotopic signature dominated by sub-continental lithosphere mantle (SCLM). Stage II basalts mark transition to an incipient oceanic rift where ocean island basalt (plume) and/or mid-ocean ridge basalt sources are diluted by SCLM. Stage III basalts are related to a mature mid-ocean ridge system where the source is dominated by the depleted asthenosphere MORB source. With this geodynamic template we examine the late Proterozoic basalts of the Catoctin Volcanic Province and identify geochemical signatures associated with two of the three stages. Although there is no radiometric data for basalts associated with the different formations, we recognize two of the stages associated with the breakup of Rodinia through the geochemical template. Basalts hosted within the Lynchburg and Ashe-Alligator Back formations are of both high (>2 wt %) and low (<2%) TiO₂ types, where the low Titanium group is best modeled as being derived from SCLM, while higher TiO₂ samples reflect a more OIB dominated source similar to the basalts of the Catoctin Formation of central and northern Virginia. Basalts of the Unicoi, Bassett and Sams Creek Formations are similar to the Catoctin Formation. These chemical signatures can be linked to Stages I and II associated with the dispersal of supercontinents.