OLIVINE GEOCHEMISTRY OF THE STATEN ISLAND SERPENTINITE

The Staten Island Serpentinite was mapped by Lyttle and Epstein (1987) as a lens shaped body whose long axis trends NE-SW. This is one of the many discontinuous ultramafic bodies that extend from Quebec, Canada into the southern Appalachians. Samples for this study were collected from an excavation for a shopping center in the Staten Island Serpentinite (N 40.58° and W 74.11°). The average composition of the serpentinite at this location is SiO₂ 34.96, Al₂O₃ 0.21, CaO 0.04, MgO 41.41, Na₂O<0.01, K₂O 0.03, Fe₂O₃ 7.66, MnO 0.01, TiO₂ 0.02, Cr₂O₃ 0.44, and LOI 15.57 sum 100.36 wt %. Benimoff and Lupulescu (2008) reported on zoned accessory Cr-Spinel in this serpentinite body. They plotted the Cr-spinel analyses in the Cr/(Cr+Al)sp vs. Mg/(Mg+Fe)sp of Coish and Gardner (2004) where the analyses plot in the forearc peridotite field. In this preliminary study we have added two new olivine analyses to the Coish and Gardner (2004) plot. Electron microprobe analyses were used to compute the following empirical formula: Mg_1.87FeO_0.16Ni_0.015(Si_0.98O₄₎. These olivine compositions average Fo₉₂. The olivine of this study plots in the ophiolitic harzburgite field in the Olivine Spinel Mantle Array (OSMA) of Coish and Gardner (2004). According to Coish and Gardner (2004) this could be interpreted as evidence for the residual origin of the peridotite represented as refractory mantle residues. This could be further evidence in support of a suprasubduction zone (SSZ) ophiolite.