Structural trends in central Britain from images of gravity and aeromagnetic fields

Abstract

Digital image processing techniques have been used to analyse the regional gravity and aeromagnetic datasets in central Britain. Colour and shaded-relief images have been generated which convey information on both anomaly amplitude (as colour) and anomaly gradient (as relief) and highlight structural trends, lineaments and textural contrasts not easily discernible on standard contour maps. We have identified some of the more important features and have tried to relate these to the evolution of the crust in each region. On a broad scale the images emphasize Caledonoid (ENE) trends to the north of the Solway line and both Tornquist (SE) and Caledonoid (NE to ENE) trends to the south. The pattern of magnetic anomalies over central England seems to define the extent of the shallow late Precambrian–early Palaeozoic basement of the Midlands Microcraton and delineates crustal elements and characteristic trends within it. Magnetic lineaments and the grain of gravity anomalies, trending in northeasterly and northwesterly directions on either side of the microcraton, seem to relate to structures which originated during the evolution of the Welsh and eastern English Caledonides respectively. Where Lower Palaeozoic and Precambrian rocks form the concealed ‘basement’, as in most of England, the gravity lineaments tend to reflect the influence of basement fractures on the subsequent pattern of sedimentation whereas many of the features on the magnetic images are more directly related to structures within the basement itself.

The concealed Caledonide basement of Eastern England and the southern North Sea — A review

“…Studies of geophysical potential field images (e.g. Lee et al 1990Lee et al , 1991Lee et al , 1993 have demonstrated that the concealed basement of eastern England is characterised by a number of SE and SSE-trending magnetic and gravity lineaments. The cause of the broad magnetic anomaly ridge extending from northern England to East Anglia (the Furness-Norfolk Magnetic Anomaly, Fig.…”

“…The cause of the broad magnetic anomaly ridge extending from northern England to East Anglia (the Furness-Norfolk Magnetic Anomaly, Fig. 1) has been the subject of much speculation (Bott 1967, Wills 1978, Allsop 1987, Cornwell & Walker 1989, Lee et al 1990, 1991. Wills (1978) referred to this feature as the Furness-Ingleborough-Norfolk Magnetic Ridge and believed it was due to the presence of magnetic metamorphic rocks, probably Precambrian, at relatively shallow depth.…”

Structural arcuation in the Berwyn Hills, North Wales

“…The Bouguer gravity anomaly field shows a distinct elongate low in the Berwyn region, visible on conventional contour maps (Figure 3; BGS 1986a) and on coloured shaded relief images (Lee et al 1990). Coincidence with a magnetic low suggested to Manchester (1983) that this may represent a subsurface granite.…”

Revealing deep structural influences on the Upper Cretaceous Chalk of East Anglia (UK) through inter-regional geophysical log correlations

“…These data have been used to compile the 1:625 000 scale gravity and magnetic maps of the UK (British Geological Survey, 2007a, b). Although regional gravity and magnetic data have been previously discussed and interpreted in the context of deep basement structure (Lee et al, 1990(Lee et al, , 1993Busby and Smith, 2001;Busby et al, 1993Busby et al, , 2006, they have not hitherto been used to understand patterns of Mesozoic sedimentation in East Anglia. Figure 7 shows a colour shaded relief residual Bouguer gravity anomaly map with the key borehole locations plotted; Figure 8 shows the same boreholes plotted on a greyscale shaded relief version of the residual Bouguer gravity anomaly map, overlain by a flat colour reduced-to-pole magnetic anomaly map.…”