Petrographic, structural, and whole-rock geochemical data from eight diabase sheets and one associated dike in the central Newark basin indicate a common petrogenesis. The petrogenetic model also can be applied to the Palisades sill in the northern Newark basin, that together with some of the central Newark basin diabases make up a single “megasheet” extending for ~150 km. Regional chill-margin compositions are extremely constant and are high-titanium, quartz-normative tholeiites (HTQ) typical of the Mesozoic eastern North America (ENA) magmatic province. On the basis of their compositional uniformity and their close similarity to many other ENA-HTQ basalts, the HTQ chills are...