| Three discrete petrologic problems are addressed in this thesis: (1) Granophyre Model: A study of Neodymium-Samarium isotope systematics in silica- and iron-enriched granophyres is consistent with a late-stage, mineral fractionation origin. Analysis of primitive mantle spider diagrams and petrographic evidence support a mechanism similar to that proposed by Helz (1987) for Kilauea Iki lava lake involving diapiric transport of silica- and potassium-rich fluids upwards through the magma, and subsequent mingling with hydrothermal fluids to produce sandwich horizon rocks. (2) Banding Model: A newly discovered 70 m-thick, rhythmically banded horizon at Alpine, NJ is characterized by alternating layers of darker, pyroxene-rich layers and light, fine-grained plagioclase-rich layers. Bulk composition corresponds to a liquidus temperature of 1200°C. The rhythmic banding event occurred during an extended period of quiescence from magmatic pulse influx. Analyses of individual rhythmic bands and normative compositions show that plagioclase-pyroxene pairs follow cotectic crystallization but correspond to cooler temperatures than the liquidus, indicating that more evolved fluid is absent from the bulk composition. Fractionation paths produced by MELTS show that the liquid is enriched in iron until the magma is cooled between 1040 and 1060°C, after which silica enrichment begins. Two residual liquids migrate upward as conjugate immiscible fluids, and are staggered by the oscillatory crystallization mechanism. (3) Multiple-Intrusion Model: Correlation of granophyres, rhythmic bands, and major element chemistry along strike shows that the Palisades magmas were emplaced in multiple pulses. Whole rock analyses are collected for over 200 samples. Internal contacts at Alpine, NJ and Piermont, NY are characterized by a sharp decrease in refractory elements and a shift from orthopyroxene to clinopyroxene fractionation. Pulse I contains 9--16 wt. % MgO, and 8--10 wt % FeO and includes the Mg-rich layer (Mg# > 0.6; Cr > 500 ppm). Pulse II contains 7--8% MgO, 11--14% FeO+Fe 2O3 and is in contact with Pulse I at the Piermont basal contact. Pulse III is an iron enriched horizon (> 15 wt. FeO+Fe2O 3) correlated geochemically with the third of the Watchung flows. Pulse chemistry relates to the Watchung flood basalts, indicating that pre-differentiated magmas were fed through open system dynamics. |
