GEODYNAMICS OF SUPERCONTINENT DISPERSAL: GEOCHEMICAL TRACERS FROM LARGE IGNEOUS PROVINCES, EASTERN NORTH AMERICA

We present new geochemical data for two LIPS associated with the dispersal of two super-continents, Rodinia and Pangea. The LIPS are represented by the late Proterozoic Catoctin Volcanic Province (CVP; Rodinia breakup) and the Mesozoic age Central Atlantic Magmatic Province (CAMP; Pangea breakup). Data for the CAMP from the Culpepper Basin of Virginia, as well as previously published data for 160 to 120 Ma and zero age Atlantic MORB define an ordered sequence of geodynamic events for the rifting of Pangea and formation and evolution of the Atlantic ocean basin. CAMP data have Nb/La (3.03-9.14) and Th/Ta (0.36-0.65), similar to island arc lavas. The isotope signatures for the CAMP show island arc-SCLM and/or lower crust affinities. As rifting progressed and the ocean basin opened up (160-120 Ma to present), Central Atlantic MORB geochemical signatures require plume pollution of their asthenosphere source. Numerous plumes, dating back to the early opening of the ocean basin, occur along the western African continental margin in the Central Atlantic. We model this source evolution to reflect 200 Ma melting of the SCLM (CAMP event) associated with a thermal anomaly related to edge effect convection and lithosphere thinning during the breakup of Rodinia, followed (<200Ma) by continued upwelling of asthenosphere and buoyant mantle plumes rooted in the peripheries of the African superswell. Comparison of incompatible element ratios between CVP basalts (e.g., Zr/Y = 4.91, Th/Ta = 1.37, Hf/Th = 2.82) and CAMP lavas (e.g., Zr/Y = 2.30, Th/Ta = 6.97, Hf/Th = 0.96), coupled with primitive mantle normalized element abundances, show CVP to have an OIB affinity similar to Hawaii, rather than SCLM. The CVP lavas define Pb-Pb isotope pseudo-binary trends between SCLM sources and a C-like OIB source. Pb isotopic ratios for CAMP have elevated ²⁰⁷Pb/²⁰⁴Pb for a given ²⁰⁶Pb/²⁰⁴Pb relative to CVP, and correlate positively with ⁸⁷Sr/⁸⁶Sr (CVP ~ 0.7035; CAMP ~ 0.706). In εNd-εHf space both CVP and CAMP define linear arrays with similar εNd, but CAMP is offset to distinctly higher εHf. We interpret the data to suggest the CAMP was derived largely from the same SCLM as the CVP source, but with no plume component. The data point to post CVP subduction related enrichment (>570 Ma, but <1 Ga) of SCLM of eastern North America prior to the CAMP event.