ORIGIN OF BASALT BRECCIAS IN THE FAIRHAVEN DIKE SYSTEM, WALLINGFORD, CT

One of three extensive dike complexes cropping out in the Mesozoic Hartford Basin, the Fairhaven dike is an en echelon system of near-vertical, northeast- trending conduits which are spatially-related to and probably have acted as feeders for the Talcott flood basalts. In the east Wallingford, CT, area, exposures of Fairhaven dike segments are comprised of basalt breccias displaying well-developed fluidal textures in the form of droplets and flame-shaped particles, as well as larger pillow-like globular masses, some of which are vesicular. These are contained in an interspersed baked matrix of sand grains and pebbles derived from the New Haven Arkose. The complete disaggregation of the sedimentary matrix and the lack of discreet arkose clasts suggest that the sediments were incompletely lithified at the time of dike emplacement and brecciation. The abundance of accidental debris from adjacent and overlying New Haven strata in these breccias is suggestive of explosive phreatomagmatic interaction of basaltic magma with wet sediment and/or groundwater, occurring where rising melt in dike conduits intersect surface or near surface wet fan sediments. Mixed blocky and fluidal peperite formed during fine scale intermixing of basaltic magma with coarser wet sediment, resulting in brittle fragmentation of magma which is still fluid during explosive magma-water interaction. The breccias record subsurface fuel-coolant interactions leading to localized explosive eruptions which most probably preceded the quiet effusion of flood basalts.