THE ORANGE MOUNTAIN FLOW, NEW JERSEY: A STRATIGRAPHICALLY ZONED DECOMPRESSED-MELT COMPOSITE BASALT

The Palisades Sill and the Watchung Flows of New York and New Jersey comprise a Sill-Eruptive igneous pairing of three major linked magma pulse events (Puffer and others, 2009). It is theorized that the Watchung Flows (NJ) possess a cumulus-linked compositional variability characteristic of pulse horizons mapped in sections of the Palisades, particularly over the lowermost 100 meters. Evaluation of the gradational mineralogy in the Orange Mountain Flow demonstrates a cryptic stratigraphic progression in mineralogy similar in extent to that present in Palisades Pulse 1. Sampling upward across the 100 meter section of the Orange Mountain exposure at Tilcon traprock quarry, Clifton, New Jersey shows an augite-ferroaugite trend varying from approximately 10% FeO_T to more than 30% FeO_T across the pyroxene quadrilateral. The associated Fe-enrichment in the subcalcic augite-to-pigeonite set is of comparable magnitude. Poorly resolved exsolution in the augite-pigeonite series is comparable to solidus exsolution experiments in the range 1160 to 1000+^oC. Rietveld x-ray diffraction refinements demonstrate an iron-enrichment trend with unit cells for augite that vary from b(Å) 8.91 to 8.99. The Orange Mountain Basalt is modeled as a heterogeneous, decompression-melted mixed unit with a remnant cumulus and an associated horizon at upper levels of hydrothermally modified diapir-emplaced and smeared tonalite-trondhjemite magma. Results support the theory that the Orange Mountain Basalt represents the through-going portion of Pulse 1 of the Palisades Section exposed close to Fort Lee, New Jersey.