Terrestrial Heat Flow and Heat Generation in South-west England

Abstract

Three heat flow values for south-west England are presented. Two of the sites, Geevor and South Crofty, are operating tin mines on the northern contacts of the Land's End and Carnmenellis Granites, respectively, while the third, Wilsey Down, is a stratigraphical borehole 5 km north of the Bodmin Moor Granite. After applying topographic corrections values of 128.6 mW m-2 (3.07 µ cal cm-2 s-1) for Geevor, 128.9 mW m-2 (3.08 (A cal cm-2 s-1) for South Crofty and 67.3 mW cm-2 (1.61 cal cm-2 s-1) for Wilsey Down, were determined. The value at Wilsey Down is shown to be consistent with that for an environment in which the Hercynian orogeny was the last significant thermal event. An additional heat source term must clearly be involved at Geevor and South Crofty to account for the unusually high values at these sites. Radiogenic heat production has been determined on granites from these sites and in spite of the fact that it is high it does not fully account for the measured heat flow. A compilation of underground temperature measurements made in the nineteenth century suggests that high heat flow is a general feature of the mineralized belt. At least part of this can be explained in terms of hot spring activity recorded widely throughout the area but the ultimate cause remains to be evaluated.