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The Flemington fault zone in the central Newark basin contains a complex system of faults consisting of both braided and en echelon segments with folds trending perpendicular and parallel to the major faults. Six basalt flows centered at three loci, and five diabase intrusions at four loci occur within a 35-km (22 mi) interval of the hanging-wall region of the fault zone. Lower basalt flows and chilled diabases are classified as low-TiO2 quartz-tholeiites; upper basalt flows are classified as high-iron quartz tholeiites. Chill-margin samples of diabase and the lower stratigraphic group of basalts match the composition of Orange Mountain Basalt. Two stratigraphically higher basalts correlate with Preakness Basalt. Differentiation models indicate that granophyric diabase can be produced from chill-margin composition by removal of pyroxene, plagioclase, and olivine, and addition of Fe/Ti-oxide, orthoclase, and quartz. Structure contouring indicates that Cushetunk Mountain and adjacent diabase stocks intrude the Passaic Formation at a low stratigraphic level, approximately the same level as the Lambertville sill. Diabase intruded into the uppermost part of the Passaic Formation at Oldwick is nearly identical to other fine-grained diabases, indicating that chemical fractionation is not related to stratigraphic height of intrusion.

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