Gravity and magnetic surveys of the younger gabbros of Aberdeenshire

Abstract

About 700 gravity and 1200 magnetic measurements have been made in north-east Aberdeenshire in order to find the attitudes of the basic intrusions. The surveys have covered the younger gabbros, the Bennachie granite and the intervening areas. A marine magnetic survey has covered an area about 40 × 30 km offshore from Banff. The Bouguer anomalies are positive over almost the whole area except the Bennachie granite; together with prominent magnetic anomalies these indicate that the exposed gabbros form part of a continuous basic sheet. This sheet varies in thickness from 1 or 2 km near Huntly to 7 km at Cabrach. Positive magnetic and negative gravity anomalies are found from Dufftown to the Moray Firth, suggesting that there are extensive granite intrusions in this area. Hidden extensions of the Cabrach mass and the Bennachie granite have been approximately delineated. Positive gravity anomalies extend from Cabrach over the northern part of the Morven mass. Models have been constructed which fit the anomalies over the Insch and Belhelvie masses; these suggest that there has been post-consolidation folding at Belhelvie. In five localities the gravity and magnetic anomalies are closely correlated and the direction of magnetization has been computed for each of these areas. These are compared with the directions found by Blundell & Read (1958) and the deformation of the basic intrusions is discussed. Gravity and magnetic anomalies at the east end of the Insch mass suggest that this mass also has been deformed.