CHARM II—A deep reflection profile within the central England microcraton

Abstract

The results of a deep reflection profile crossing the Precambrian rocks of Charnwood Forest and the postulated buried Caledonian Mountsorrel granodiorite in central England are reported. A prominent subhorizontal reflector to the NE of Charnwood Forest is suggested as marking the base of the pre-Carboniferous Widmerpool Gulf, and possibly arises from the top surface of the granodiorite intrusion. A lack of returned energy from the upper crust beneath Charnwood Forest contrasts with a mass of reflectors beneath the intrusion, which itself appears relatively transparent to seismic energy. Two subparallel bands of reflectors within the lower crust, continuous across the whole profile and previously observed on another section about 20 km to the east, suggest that the emplacement of the granite has caused little disturbance within the lower crust in the plane of the section. The origin of the twin reflections is unexplained. Similar twin reflections occur in the lower crust in northern Germany immediately to the SE of the London–Brabant massif over whose NW region the CHARM profile was sited.