TALE OF TWO SPATIALLY OVERLAPPING LARGE IGNEOUS PROVINCES, EASTERN NORTH AMERICA: DECIPHERING THE ROLE OF SUB-CONTINENTAL MANTLE IN THEIR ORIGINS

The central Appalachian orogen is a globally unique region which provides a geologic record of assembly and dispersal of two super-continents, Rodinia and Pangea. For each super-continent dispersal, Large Igneous Provinces (LIPS) are represented by the late Proterozoic Catoctin Volcanic Province (CVP; associated with breakup of Rodinia) and the Mesozoic age Central Atlantic Magmatic Province (CAMP; breakup of Pangea). Both these magmatic provinces are nearly co-incident in their location within the region, and provide an opportunity to evaluate mantle processes and sources over time. Trace element and isotopic data for the CVP lavas are distinct from basalts associated with CAMP. A comparison of incompatible element ratios between CVP basalts (e.g., Zr/Y = 4.91, Th/Ta = 1.37, Hf/Th = 2.82) and CAMP (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 like Hawaii. In contrast CAMP data e.g. Nb/La (3.03-9.14) and Th/Ta (0.36-0.65), are similar to island arc lavas. New data for Pb, Sr, Nd and Hf isotopes also reflect differences. In Pb isotope space CVP lavas define a pseudo- binary trend between continental lithosphere-like sources and a C-like OIB source. Lead isotopic ratios for CAMP have elevated 207Pb/204Pb for a given 206Pb/204Pb relative to CVP, and correlate positively with 87Sr/86Sr (CVP ~ .7035; CAMP ~ .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 record a subduction related enrichment event (>570 Ma, but <1 Ga) of SCLM of eastern North America (east of the New York – Alabama lineament) leading to a heterogeneous lithosphere. The OIB trace element signature and elevated 206Pb/204Pb for CVP suggest mixing of both depleted and enriched SCLM with a C-like plume component. In contrast, the more continental lithosphere-like Pb isotopes, and arc-like trace element signature suggest the CAMP were derived largely from the same continental lithosphere source with no recognizable plume component. The higher εHf for CAMP relative to CVP suggests derivation from the residual source of the CVP lavas. The CVP and CAMP lavas record a globally unique ordered sequence of enrichment, depletion and mixing events from Grenville through Mesozoic time.