BREAKUP OF SUPERCONTINENT RODINIA - RIFT TO DRIFT ASSOCIATED MAGMATISM

The breakup of supercontinents is accompanied by magmatism associated with various geodynamic scenarios. Rift to drift transition during late Proterozoic breakup of Rodinia in the region of the central Appalachian orogen is recorded as flood basalts and interlayered basalts in sedimentary rocks which represent near shore to distal portions of the continental margin. Geochemical and isotopic signature of flood basalts of the Catoctin Volcanic Province (CVP) and amphibolites in sedimentary formations are used to identify the temporal tectono-magmatic stages associated with dispersal. We model Stage I basalt generation during incipient supercontinent extension when chemical/isotopic signature is dominated by sub-continental lithosphere mantle (SCLM). Stage II basalts mark transition to an incipient oceanic rift where Ocean island basalt (plume) 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 depleted asthenosphere MORB source. Our isotopic and geochemical data from the flood basalts of the Catoctin Formation (type area of CVP) show incompatible element ratios of Zr/Y = 4.91, La/Yb = 5.73, Th/Ta = 1.37 and Hf/Th = 2.82, as well as primitive mantle normalized trace element abundances with OIB affinity like Hawaii. These lavas have similar low Nb/La (0.63-1.04) as Hawaii but slightly higher Th/Ta (1.1-2.12), and in Pb-Pb isotope space define a pseudo- binary trend between SCLM-like sources and an OIB source similar to a C-like plume component suggestive of Stage II. Amphibolites in the Unicoi, Bassett and Sams Creek Formations, are also modeled as Stage II magmatism. Other amphibolites 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 Stage I, while higher TiO₂ samples reflect Stage II OIB dominated source. Kennett Square amphibolites show Stage III geochemical signature and represent Iapetus ocean floor basalts thrust on the continental margin during the mid-Ordovician Taconic orogeny. Recognition of these temporal geodynamic stages is critical in meeting EarthScope and GeoPrisms objectives for eastern North America.