CORRELATION OF FOUR PALISADES MAGMAS WITH OVERLYING BASALT FLOWS, NEWARK BASIN, NEW JERSEY AND NEW YORK

The Palisades Intrusive System consists of a 350 m thick early Jurassic composite sill together with thinner co-magmatic sills and dikes exposed within the Newark Basin of New Jersey and New York. The Palisades System is overlain by flood-basalts that are interbedded with early Jurassic red-beds. New and recently published geochemical data indicate that some of the basalt flows correlate with geochemically defined layers within a central well exposed sill portion of the Palisades System at Fort Lee, New Jersey. Our interpretation views the Fort Lee exposure as a conduit through which huge volumes of flood-basalt flowed during extrusion over a prolonged period of time.

The upper and lower chilled margins of the Fort Lee exposure and the Orange Mountain basalt flows are typical ITi-type CAMP tholeiites. Three interior Palisades layers correlate with chemically diverse Preakness basalt flows that overlie the Orange Mountain basalt. The upper interior Palisades layer and the first Preakness flow are each 160 m thick and have each undergone considerable in-situ fractionation. A mid-interior Palisades layer and the second Preakness flow are each 80 m thick and are chemically similar. A lower interior Palisades layer and the upper Preakness flows are typical LTi-type CAMP tholeiites and are 55 m thick.

Although exposures of Preakness and Orange Mountain basalt that are distal to their fissure source are separated by as much as 155 m of red-beds deposited over about 260 ky, exposures close to the Palisades fissure source indicate that Orange Mountain magmatism continued intermittently until shortly before the first Preakness magmatism. Aggressive flow of the massive first pulse of Preakness magma through the Palisades conduit eroded most diabase of Orange Mountain composition at Fort Lee leaving only the chilled margins as evidence. However, sections through the Palisades exposed north of Fort Lee indicate considerable variation in layer thickness and the involvement of additional pulses of magma.