Granite beneath Market Weighton, east Yorkshire

Abstract

A NE-SW elongated negative gravity anomaly of 40 x 20 km 2 areal extent and –15 mgal amplitude occurs near Market Weighton. Thick sediments and salt can both be ruled out as main source of the anomaly using the known geology and depth to magnetic basement. Interpretation in terms of an underlying granite batholith is supported by the pattern of second derivatives and by comparison of gravity and magnetic anomalies. The postulated Market Weighton granite intrudes the pre-Carboniferous basement and extends to more than 8 km depth. The granite penetrates the northern flank of a belt of magnetic basement rocks that give rise to a positive magnetic anomaly extending from west of the Pennine Askrigg Block to the Wash. Local magnetic highs to northwest and south of the granite are attributed to strongly magnetized basement rocks abutting against more weakly magnetized granite, analogous to the southwestern margin of the Wensleydale granite. An apparently locally thinned Carboniferous succession in the Market Weighton region can be attributed to the tectonic influence of the buoyant granite during the Carboniferous. Although the granite is not located centrally beneath the Jurassic and Lower Cretaceous stable block, nevertheless it provides a plausible mechanism for the stability, in association with basement faulting and tilting.