Abstract
Summary: Gravity and magnetic surveys show the presence of the following major basement features beneath the Lower Carboniferous rocks of the northern Pennines: (1) the Devonian Weardale Granite underlies the Alston Block and has been reached by the Rookhope borehole; (2) a belt of east-south-easterly trending magnetic basement rocks underlies the southern half of the Askrigg Block at shallow depth and extends laterally beyond the block at greater depth; (3) the postulated Wensleydale Granite underlies the Askrigg Block centrally and pierces the northern flank of the magnetic basement rocks; (4) gravitationally and magnetically featureless basement rocks (possibly Lower Palaeozoic overlain by thick Carboniferous) occur between the blocks; and (5) the basement is relatively shallow beneath the Alston and Askrigg blocks but deepens rapidly with associated thickening of the Lower Carboniferous rocks across the following hinge-lines—Ninety-Fathom-Stublick fault line, Lunedale—Butter-knowle fault line, Stockdale monocline, and (from geological evidence) Craven fault belt. Since the basement is overlain by a particularly well studied cover of Carboniferous rocks, the northern Pennines provide a unique demonstration of the influence of granites on the structural history long after consolidation. The basement features, which both include granites, have exerted close control of major and minor faulting, doming and uplift, basin formation and distribution of mineralization. This is attributed to (1) the relatively greater “strength” of the granites and magnetic basement rocks, (2) the supplementary stress systems set up by the low density granites and by the topographic irregularities, and (3) incipient jointing in the Weardale Granite providing an easy upward passage for mineralizing solutions.

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