Theoretical Study of the Heat of Transport in a Liquid Ni50Al50 Alloy: Green-Kubo Approach

We analyse the formalism of transport in a binary system especially focussing on a detailed consideration of the heat of transport parameter characterizing diffusion driven by a temperature gradient. We introduce the reduced heat of transport parameter Qc*' which characterizes part of the interdiffusion flux that is proportional to the temperature gradient. In an isothermal system Qc*' represents the reduced heat flow (pure heat conduction) consequent upon unit interdiffusion flux. We demonstrate that Qc*' is independent of reference frame and is practically useful for direct comparison of simulation and experimental data from different sources obtained in different reference frames. Then, we use equilibrium molecular dynamics simulations in conjunction with the Green-Kubo formalism to study the heat transport properties of a model of the liquid Ni50Al50alloy at three state points within the temperature range 1500 – 4000 K. Our results predict that in the liquid Ni50Al50alloy in the presence of a temperature gradient Ni tends to diffuse from the cold end to the hot end whilst Al tends to diffuse from the hot end to the cold end.

New heat flow density and radiogenic heat production data in the Canadian Shield and the Quebec Appalachians

New heat flow density (HFD) measurements were performed at 10 sites in Quebec. For five of the sites located in the Superior Province, the heat flow density varies between 24 and 35 mW/m2 (26 and 37 mW/m2 after adjustment for Pleistocene climatic variations). In the Grenville Province, the values obtained range between 25 and 28 mW/m2 (29 and 31 mW/m2 after adjustment). For two nearby sites in the Gaspé region (Appalachians), the heat flow density is 47 mW/m2 (48 mW/m2 after adjustment). Radiogenic heat production was also measured. At the sites located in the meta-volcano-sedimentary sequences of the Superior Province, the heat production is low (0.1–0.6 μW/m3) and it does not always correlate with the surface heat flow. In the Grenville Province, the HFD is close to (slightly higher than) the reduced heat flow of the Superior. The higher HFD in the Appalachians is partly explained by the higher crustal heat production, and partly by higher deep heat flow.

Heat flux measurements in southwestern British Columbia: the thermal consequences of plate tectonics

Measured heat fluxes from previously published data and 34 additional boreholes outline the terrestrial heat flow field in southern British Columbia. Combined with heat generation representative of the crust at 10 sites in the Intermontane and Omineca belts, the data define a heat flow province with a reduced heat flow of 63 mW m−2 and a depth scale of 10 km. Such a linear relationship is not found or expected in the Insular Belt and the western half of the Coast Plutonic Complex where low heat fluxes are interpreted to be the result of recent subduction. The apparent boundary between low and high heat flux is a transition over a distance of 20 km, located in Jervis Inlet 20–40 km seaward of the Pleistocene Garibaldi Volcanic Belt.The warm, thin crust of the Intermontane and Omenica Crystalline belts is similar to that of areas of the Basin and Range Province where the youngest volcanics are more than 17 Ma in age. Processes 50 Ma ago that completely heated the crust and upper mantle could theoretically produce such high heat fluxes by conductive cooling of the lithosphere. But it is more likely that the asthenosphere flows towards the subduction zone, bringing heat to the base of the lithosphere. Since the reduced heat flow is high but constant, large differences in upper crustal temperatures within this heat flow province at present are caused by large variations in both crustal heat generation and near-surface thermal conductivity. The sharp transition in heat flux near the coast is the result of the combined effects of convective heating of the eastern Coast Plutonic Complex, pronounced differential uplift and erosion across a boundary within the Coast Plutonic Complex, and the subducting oceanic plate.

Heat flow in a back-arc environment: Intermontane and Omineca Crystalline belts, southern Canadian Cordillera

A suite of 20 heat flow measurements has been completed across the Intermontane and Omineca Crystalline belts in south-central British Columbia at about 50°N. Values along the 200 km line are high (83 mW m−2, corrected for Pleistocene glacial climate; reduced heat flow is 67 mW m−2) and uniform (standard deviation = ± 10%). There appears to be no difference in the thermal structure of the two geologic belts. Two sources of heat are considered to explain the level of heat flow observed: a discrete thermal event in the Eocene, and a steady-state supply of heat maintained in the back-arc location by asthenospheric flow caused by nearby subduction. Both can account equally well for the elevated heat flow observed. However, in light of seismic, magnetic, electrical, and flexural data that suggest that the lithosphere may be as thin as 30–40 km, it is concluded that a steady supply of heat must exist since this thickness is much less than the thickness of lithosphere that would be present 50 Ma after even a major thermal event.

Geothermal measurements in Newfoundland

We report heat flow values for ten holes at five sites in Newfoundland. The average observed heat flow is 43 ± 4 mW m−2. Corrected for Pleistocene surface temperature variations, the average becomes 50 ± 4 mW m−2, with a range from 38–82 mW m−2. The Dunnage zone (a vestige of the Iapetus Ocean) exhibits a heat flow lower than normal for Paleozoic orogenic belts. The highest heat flow is associated with the Carboniferous St. Lawrence granite intrusion. Heat production measurements were made at three of the sites. Those in the Dunnage zone are low (< 0.8 μW m−3), as expected for former oceanic rocks, while that for the St. Lawrence granite is high (4.9 μW m−3). A plot of heat flow versus heat production for these data and the data of Hyndman et al. for the Maritime Provinces demonstrates that Newfoundland belongs to the same heat flow province as the Maritimes and the eastern United States. The reduced heat flow for the Canadian Atlantic Provinces data is 32 ± 3 mW m−2, uncorrected, and 40 ± 3 mW m−2 when corrected for Pleistocene temperature effects. Computed geotherms for heat flows and heat productions corresponding to the upper and lower observed limits of the data yield temperatures at 30 km depth of about 575 and 475 °C respectively.