Digital image processing and isostatic studies of the regional gravity field of Great Britain and adjacent marine regions

Abstract

This thesis presents the results of an investigation into the regional gravity field of Great Britain and the adjacent regions. A prerequisite for this study was the development of a computer database designed to store, manipulate and display the information contained within nearly 400,000 gravity and topography point observations for the region. Digital image processing techniques have been applied to the reduction and display of the Bouguer anomaly data. The observed Bouguer anomaly lineaments display a pattern of geological basement structures which correlates closely with those predicted by recent plate tectonic models of the Lower Palaeozoic Caledonian orogeny which assume the convergence of three distinct continental plates. The nature of the isostatic compensation of the topography in the vicinity of the United Kingdom has been investigated using cross spectral analysis of the gravity and topography. The observed cross spectral relationships are compared with those for a theoretical isostatic model which assumes the lithosphere behaves like a thin elastic plate loaded by both surface topography and internal density contrasts overlying an inviscid fluid substratum. For a uniform elastic thickness of the continental lithosphere the best fit between the observed and theoretical relationships is obtained for values of the elastic thickness of the lithosphere of 22.5-24.5 km. A better fit is obtained if the continental lithosphere is assumed to comprise a population of distinct tectonic provinces of equal area with the values of the elastic thickness of the lithosphere for the provinces distributed uniformly between 6-8 km and 86-90 km. Detailed investigations into the structure of the crust beneath the Tertiary igneous complexes of Mull and Skye, northwest Scotland, indicate a possible slight thickening of the crust which is considered to be an important consequence of the mechanism of the emplacement of the complexes.