GEOCHEMISTRY OF THE METAMORPHOSED SPRING POINT AND CUSHING FORMATIONS

The Casco Bay Group is mapped along the southern coast of Maine, from Portland north to Bath. Several different metamorphic field gradients are present, from chlorite grade up through staurolite grade indicating that pressure and temperature conditions varied along the coast. This study focused specifically on the petrology of the Spring Point and the Cushing Formations in the Casco Bay Group.

Hussey (1988) has suggested that these formations originated as volcanics on an island arc off the coast of present day Maine. This project tests this hypothesis with geochemical data analysis. Bulk rock geochemistry by ICP-MS for twenty samples identified major, trace and rare earth elements. Discriminatory diagrams prepared from this data determined that the protoliths were andesites to basalts. The basalts range from subalkaline to calc-alkaline, and represent volcanic arc flow with considerable sediment influence.