Multiple Dikes of Cape Neddick

Abstract

Cape Neddick lies on the southwest coast of Maine in York County. The Kittery quartzite crops out around nearly the entire periphery of the cape and contains a large number of structurally complicated multiple dikes. The quartzite in this area has been intruded by a soda granite and by the Cape Neddick gabbro. Each of these intrusives contains its own suite of dikes whose members are not, however, involved in multiple relationship with one another. Most of the multiple dikes strike nearly northeast, are nearly vertical, and are characterized by strong parallelism. Both structures and lithological associations were studied to determine features peculiar to these dikes. Certain types of behavior, for example, that called by the writer “braiding” and “intrasectate” and “extrasectate” combination, were found to be typical. No structural peculiarities in the host rock which might have localized the multiple dikes could be detected. The condition necessary for their formation is believed to be the repetition of periods of essentially parallel fracturing in association with periods of magma availability. The study suggests that recurrent fracturing and contemporaneous intrusion of magmatic differentiates are probably strictly interdependent phases of the dike-building activity. The cause of this activity must eventually be sought in the behavior and influence of subjacent igneous masses previously active in the area.