Seismic reflection, gravity and magnetic studies of the geology of the East Midlands.

About 100 km of seismic reflection sections down to 1 sec commercially produced for the NCB for prospects at Loughborough, East Leicestershire and Amington were interpreted. The Loughborough data show a NW-SE syncline, six principal faults, and thin Coal Measures. The East Leicestershire data show considerable undulations up to 200 m and an E-W fault. Variable Coal Measures 75--175 m thick existed throughout the area. Eleven coal seams up to 3.5m thick reflects the economic potential of the area. Three diorite horizons and Mountsorrel granite work type are encountered. The Amington data show undulations which increase in complexity downwards, five faults with throws up to 60 m, and relatively thin coal seams. Raw gravity data for the 3000 km2 between 41--46E and 29--35N were checked, contoured and then gridded at 0.5 km to produce 101 x 121 array which was used for processing. Ten profiles were selected for spectrum analyses and showed that the main gravity data features could be explained in terms of structures at depths of 1.3, 3.5, 6.6, 9.5 and 17.3km. Wavelength filtered, upward and residual maps indicate a NW-SE regional trend and suggest various densities for the Charnian rocks, and northern extension of the Warwickshire Coalfield. The downward continuation estimated the depth to the different gravitating sources. The second derivative estimated the width of the different structures. The lateral density variations using polynomials produced a new Bouguer map on which most of the anomalies were shifted and matched the known geology. A 2D-model along a 50 km profile shows a faulted layered basement which includes intrusives overlain by folded and faulted sediments. The aeromagnetic map of the area was digitised at 1 km intervals and used to produce a reduced to the pole map which was processed. The main feature of the magnetic basement shown by the maps is a NW-SE trough with its deepest part around Ashby. The spectral analysis, filtering and continuation techniques confirmed the gravity results and suggested that the diorites in Charnwood and South Leicestershire are more extensive than the outcrops indicate. The second derivative was useful for outlining the shapes of the magnetic sources. The Mountsorrel granite appears to extend considerably to the east, north and west by about 15 km at an estimated 2D-model depth of 1.3 km in the NW.