Terrestrial Heat Flow and Heat Generation in South-west England

Tammemagi, Hans; Wheildon, J.

doi:10.1111/j.1365-246x.1974.tb04110.x

Cited by 38 publications

(11 citation statements)

References 24 publications

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“…James (1944) showed that temperature gradients are very high in the mines of the Cornubian Peninsula; excluding one much lower value, the range of 20 values that he quoted was from 24 to 76ºCkm -1 , averaging 43ºCkm -1 . Tammemagi and Wheildon (1974) reported corrected heat flow values in granites of 134.8 mWm -2 at the Geevor Mine (Land's End pluton) and 137.7 mWm -2 at the South Crofty Mine (Carnmenellis pluton). Those authors suggested that the high heat flow could be related to the convection of hydrothermal fluids in the belt of mineralization that runs from Land's End past the northern end of the Carnmenellis pluton, in which the measurements were made.…”

Section: Geophysical Properties Of the Cornubian Granitesmentioning

confidence: 99%

The Cornubian Batholith: an Example of Magmatic Fractionation on a Crustal Scale

Chappell¹,

Hine²

2006

Resource Geology

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Abstract:The Cornubian Batholith comprises six major and several smaller bodies of S-type granite in southwestern England. These late-Variscan granites comprise two-mica granites, and much less abundant Li-mica granites that are restricted to one of the major bodies (St Austell) and smaller bodies. Some of these intrusive rocks are associated with major Sn mineralization. This paper is concerned with the geochemistry of the two-mica granites, which are felsic, strongly peraluminous, and have a high total alkali content and low Na:K. Rocks with very similar compositions to these granites occur elsewhere, including the Variscan granites of continental Europe, and in southeastern Australia. In detail all of the major plutons of this batholith have distinctive compositions, except for Bodmin Moor and Carnmenellis which cannot be discriminated from each other compositionally. A comparison with experimental data shows that the granites attained their major element composition under conditions of crystalliquid equilibrium, with the final melt being saturated in H 2 O, at temperatures close to 770°C and pressures about 50 MPa. That temperature estimate is in good agreement with values obtained from zircon saturation thermometry. The specific minimum-temperature composition excludes the possibility of widespread transfer of elements during hydrothermal alteration. Minor elements that are relatively very abundant are Li, B, Cs and U, while F, Ga, Ge, Rb, Sn, Ta, W and Tl are quite abundant and P is high for felsic rocks. Sr, Ba, and the trace transition metals Sc to Zn, are low, but not as low as they commonly are in very felsic granites. These trace element abundances, and the H 2 O-saturation, resulted from the fractional crystallization of a melt derived by the partial melting of feldspathic greywackes in the crust. The Cornubian granites have compositions very similar to the more felsic rocks of the Koetong Suite of southeastern Australia, where a full range of granites formed at the various stages of magmatic fractionation postulated for the Cornubian granites, can be observed. The operation of fractional crystallization in the Cornubian granites is confirmed by the high P abundances in the feldspars, with P contents of the plagioclase crystals correlating with Ab-content. Most of the granites represent solidified melt compositions but within the Dartmoor pluton there is a significant component of granites that are cumulative, shown by their higher Ca contents. The Cornubian plutons define areas of high heat flow, of a magnitude which requires that fractionated magmas were transported laterally from their sources and concentrated in the exposed plutons. The generation of these granite plutons therefore involved magmatic fractionation during the stages of partial melting, removal of unmelted material from that melt, and fractional crystallization. During the later stages of those processes, movement of those magmas occurred on a crustal scale.

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Section: Geophysical Properties Of the Cornubian Granitesmentioning

confidence: 99%

The Cornubian Batholith: an Example of Magmatic Fractionation on a Crustal Scale

Chappell¹,

Hine²

2006

Resource Geology

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“…Anomalously high heat flow values based on temperature measurements made at various levels in two mines, have been reported from South-west England (Tammemagi & Wheildon 1974). It is the purpose of ihis study to verify the above results utilizing data obtained from surface exploration boreholes, and also to further delineate the zone of high heat flow.…”

Section: Introductionmentioning

confidence: 99%

“…Thermal conductivities were measured on core samples from boreholes 0, P, E and BKML4 using a divided-bar apparatus and standard techniques (see Tammemagi & Wheildon 1974, for details) and the results are depicted in Fig. 3 .…”

Section: Conduc-heatmentioning

confidence: 99%

Further data on the South-west England heat flow anomaly

Tammemagi

Wheildon

1977

Geophys J Int

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Summary.Temperature gradients and thermal conductivities were determined for a number of exploration boreholes in South-west England in order to verify and further delineate the anomalously high heat flow which has been reported. A pattern is emerging of an anomalously high geothermal gradient and heat flow of about 4OoCh-' and 126mWm-' respectively over the Hercynian granite batholith, with normal values adjacent to it. A synthesis of related data indicates that the heat flow anomaly is associated with convection of hydrothermal fluids and although the mechanism is not well understood it may be caused by a combination of above average natural radioactive heat generation coupled with deep, permeable fracture systems within the batholith.

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“…The two mine sites (South Crofty: SCM and Geevor: GM) both produce anomalously high heat flows. Tammemagi and Wheildon (1974) report that the temperature measurements were made in horizontal and inclined boreholes at various levels throughout the mines. They discussed the possibility that the extensive period of mining would have led to disturbed temperatures in the mine that might have affected virgin rock temperatures.…”

Section: Heat Flowmentioning

confidence: 99%

“…It was recognised that this could cause problems due to ground water flow, deep weathering and recent climate change. These data were supplemented by measurements in mines at South Crofty and Geevor, where access to much greater depths was possible (Tammemagi and Wheildon 1974). These combined results were published in summaries of the UK heat flow (Lee 1986;Lee et al 1987) and it is these publications which have been widely cited when referencing these data.…”

Section: Introductionmentioning

confidence: 99%

The Cornubian geothermal province: heat production and flow in SW England: estimates from boreholes and airborne gamma-ray measurements

Beamish

Busby

2016

Geotherm Energy

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The Cornubian granite batholith provides one of the main high heat production and flow provinces within the UK. An extensive programme of borehole measurements was undertaken in the 1980s to characterise the geothermal resource. Here we revisit the published data on heat flow and heat production from 34 boreholes and revise the published heat flow values in accord with modern palaeoclimate knowledge. This leads to a more rigorous (and increased) set of estimated temperatures at depth across the granite outcrops. Predicted temperatures at a depth of 5 km largely exceed 200 °C and are 6-11 % higher than previously estimated values. We also reconsider the borehole heat production values in conjunction with new heat generation information from a recent regional-scale airborne geophysical survey. The radiometric (gammaray) data provide detailed (~70 m along-line) ground concentration estimates of the heat-producing radioelements. These are then combined to estimate heat production in the near surface. The airborne estimates are subject to attenuation by the soil profile. Here we demonstrate and then adopt an assumption that the observations of the soilbedrock medium undergo a flux attenuation by a factor of about two compared to the response of the underlying material. The revised estimates are then correlated with their equivalent deeper borehole estimates. Linear regression is then used to correct the shallow airborne estimates to values that are consistent with the deeper borehole determinations. The procedure provides a detailed and extensive mapping of heat production at both on-and off-granite locations across SW England. The Dartmoor and Land's End granite offer the greatest spatial geothermal potential in terms of their intrinsic radionuclide concentrations and associated heat production. District-scale heat production is studied using the airborne data acquired uniformly across conurbations. The analysis identifies the towns of Camborne, Penzance, St. Austell, Redruth and St Ives as having relatively high values (>4 μW m −3 ) within their urban perimeters.

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Terrestrial Heat Flow and Heat Generation in South-west England

Cited by 38 publications

References 24 publications

The Cornubian Batholith: an Example of Magmatic Fractionation on a Crustal Scale

The Cornubian Batholith: an Example of Magmatic Fractionation on a Crustal Scale

Further data on the South-west England heat flow anomaly

The Cornubian geothermal province: heat production and flow in SW England: estimates from boreholes and airborne gamma-ray measurements

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