GEOCHEMICAL INVESTIGATION OF THE BYRAM DIABASE

The Newark basin is a failed rift in northern New Jersey composed of sedimentary units, and basalt flows, and shallow intrusives (diabases). The Byram Diabase is one rock unit in the Newark basin that is exposed in between the sedimentary units along the Delaware River between Stockton and Frenchtown. Field exposures of the unit indicate no evidence of layering or flow structure. However, significant grain size variations (from 3 mm to << 1 mm) are observed in several locations. The aim of this study is to find a reason for the difference in grain size and to see if it may be related to the difference in chemical composition between the large and small grained rocks. Petrographic examinations suggest that the mineralogy of the samples is the same regardless of grain size. Some of the coarser-grained diabase samples have higher percentages of MgO, Cr₂O₃ and slightly higher percentages of SiO₂ but lower percentages in CaO, Al₂O₃, Na₂O, K₂O, MnO, TiO₂ and P₂O₅. This was coupled with lower amounts of most trace elements including the high field strength elements and rare earth elements.