GEOCHEMICAL AFFINITY OF MESOZOIC DIABASE DIKE SEGMENTS IN BETHANY, CT
We have examined several geographically isolated diabase dike segments in Bethany, CT which trend north-northeast and are intruded into the Golden Hill Schist, Harrison Gneiss and Ordovician granites just west of the Hartford Basin. The Bethany dike segments are typically 3-5 meters wide and can be traced continuously in outcrop for up to several hundreds of meters. Geologic mapping of these intrusive bodies reveals some variations from the outcrop pattern represented on the geological compilation map published by the State of Connecticut (Rodgers, 1985). Geographic separation of the Bethany dike segments from the major dike systems of the region makes their magmatic association ambiguous. They trend parallel to, but are ~2-5 km east of major segments of the Bridgeport-Pelham dike system exposed adjacent to Rock Rimmon in Beacon Falls, are ~4 km west of the West Rock Ridge sill which is comagmatic with the Fairhaven-Higganum dike, and are ~8 km west of and parallel to the Buttress-Ware dike system. Chemical data, on the other hand, provide a clearer picture of magmatic association. Samples from the Bethany dike segments are relatively unaltered and show a narrow range of chemical compositions which averages: SiO2 =50.1%, TiO2=1.35%, Al2O3=13.6%, Fe2O3T= 16.0%, MgO = 5.9%, CaO= 10.1%, Na2O=2.0%, K2O= 0.40%, P2O5=0.14%, LOI=0.08%. The compositions fall within the much broader array of compositions reported for the Bridgeport-Pelham dike system by Philpotts and Martello (1985) and clearly tie the Bethany dike segments to that intrusive suite.