GEOCHEMICAL CHARACTERIZATION OF THE MANHATTAN SCHIST AND ITS DISTRIBUTION THROUGHOUT MANHATTAN, NEW YORK

New geochemical analyses of bedrock from Manhattan, New York support a more widespread distribution of the Manhattan Schist than indicated on most geologic maps of New York City including Schuberth (1967); Baskerville (1994); and Merguerian (1996). Thirty nine representative samples from locations throughout Central Park display a smooth distribution from biotite and muscovite-enriched schist to more felsic segretations with no evident demarcation of trend to support the division of this lithology into two chemically distinguishable formations. Plots of K₂O/Na₂O vs. SiO₂ and K₂O/Na₂O vs. SiO₂/Al₂O₃ on the tectonic setting discrimination diagrams of Roser and Korsch (1986) are consistent with a passive margin to active continental margin depositional setting. Major elements also plot within the compositional field of the Martinsburg Formation, an Ordovician, largely continental shelf meta-pellite and a probable stratigraphic correlative of Manhattan Schist. In addition, samples mapped as Hartland Formation collected west of Central Park along the Hudson River plot together with the Central Park samples. An arc detritus depositional setting as generally proposed for Hartland deposition is notably un-represented. Our geochemical data together with ambiguous Hartland/Manhattan schist petrology underscores the need to establish reliable mappable criteria capable of distinguishing schist members within the Hartland from those shown here to be characteristic of the Manhattan Schist.