GEOCHEMICAL, PETROLOGIC, AND STRUCTURAL EVIDENCE FOR MAGMATIC PLUMBING IN THE MORGANTOWN PLUTON AND JACKSONWALD SYNCLINE, WESTERN NEWARK BASIN, CENTRAL ATLANTIC MAGMATIC PROVINCE, USA

The Morgantown Pluton (MP), a ~400 km^2 complex of diabase intrusions, and the Jacksonwald Syncline (JS), which contains a basalt flow and three hypabyssal diabase intrusions, comprise a magmatic center at the western end of the Newark Basin within the 200-Ma Central Atlantic Magmatic Province (CAMP). Two important parts of the MP are the ~15 km wide, ~300 m thick sill which forms the southern side and the ~20 km long, ~200 m thick Birdsboro Dike (BD) which forms the northeastern side. Both the JS and MP were tilted NNW toward the border fault after crystallization; erosion has removed any lava flows above the MP and exposed progressively deeper levels of intrusion towards the SSE. The southern sill intruded ~5 km below the paleosurface, and the dike today extends from the sill to near the border fault, possibly along a Paleozoic tear fault. Geochemical, petrologic, and structural observations are used to understand how magma filled and differentiated within the MP-JS system. New geochemical data confirm the MP and JS as CAMP high-Ti quartz-normative tholeiite. REE patterns of chill margin diabase and JS basalt are virtually identical to other Newark Basin HTQ chills and the Orange Mtn basalt, consistent with derivation of very large volumes of magma from a common mantle source to establish the magmatic plumbing. The MP sill contains a site of accumulation of orthopyroxene phenocrysts that formed repetitive opx-plag layers extending at least 150m vertically. alphaMELTS modeling of chill margin liquid crystallizes opx only at high P, supporting the interpretation from other parts of the CAMP that magma intruded as a slurry of liquid and opx phenocrysts. Field observations of magma replenishments and vertical channels of opx-rich mafic diabase that traverse the layering suggest magma recharge at the sill floor. This is supported by preliminary measurements of plagioclase-plagioclase-pyroxene dihedral angles that suggest the floor cooled more slowly than the sill interior. Diabase samples from the BD interior have more evolved compositions that cannot be explained by fractional crystallization within the dike. We use alphaMELTS modeling and mineral zoning patterns obtained by SEM-EDX analysis to evaluate models of fractionation, melt migration, and mixing to produce observed diabase compositions.