The heat flow through oceanic and continental crust and the heat loss of the Earth

Abstract

Simple thermal models based on the creation and cooling of the lithosphere can account for the observed subsidence of the ocean floor and the measured decreased in heat flow with age. In well‐sedimented areas, where there is little loss of heat due to hydrothermal circulation, the surface heat flow decays uniformly from values in excess of 6 µcal/cm² s (250 mW/m²), for crust younger than 4 Ma (4 m.y. B.P.), to close to 1.1 µcal/cm² s (46 mW/m²) through crust between 120 and 140 Ma. After 200 Ma the heat flow is predicted to reach an equilibrium value of 0.9 µcal/cm² s (38 mW/m²). The surface heat flow on continents is controlled by many phenomena. On the time scale of geological periods the most important of these are the last orogenic event, the distribution of heat‐producing elements, and erosion. To better understand the effects of age, each continent is separated into four provinces on the basis of radiometric dates. Reflecting the preponderance of Precambrian crust, two of these provinces cover the Archean to the middle Proterozoic, and the third covers the late Proterozoic to the Mesozoic. The mean heat flow decreases from a value of 1.84 µcal/cm² s (77 mW/m²) for the youngest province to a constant value of 1.1 µcal/cm² s (46 mW/m²) after 800 Ma. The nonradiogenic component of the surface heat flow decays to a constant value of between 0.65 and 0.5 µcal/cm² s (25 and 21 mW/m²) within 200–400 Ma. Using theoretical models, we compute the heat loss through the oceans to be 727 × 1010 cal/s (30.4 × 1012 W). The comparison between the theoretical and measured values allows an estimate of 241 × 1010 cal/s (10.1 × 1012 W) for the heat lost owing to hydrothermal circulation. We show that the heat flow through the marginal basins follows the same relation as that for crust created at a midocean spreading center. These basins have a corresponding heat loss of 71 × 1010 cal/s (3.0 × 1012 W). The heat loss through the continents is calculated from the observations and is 208 × 1010 cal/s (8.8 × 1012 W). Our estimate of the value for the shelves is 67 × 1010 cal/s (2.8 × 1012 W). The total heat loss of the earth is 1002 × 1010 cal/s (42.0 × 1012 W), of which 70% is through the deep oceans and marginal basins and 30% through the continents and continental shelves. The creation of lithosphere accounts for just under 90% of the heat lost through the oceans and hence about 60% of the worldwide heat loss. Convective processes, which include plate creation and orogeny on continents, dissipate two thirds of the heat lost by the earth. Conduction through the lithosphere is responsible for 20%, and the rest is lost by the radioactive decay of the continental and oceanic crust. We place bounds of between 0.6 and 0.9 µcal/cm² s (25 and 38 mW/m²) for the mantle heat flow beneath an ocean at equilibrium and between 0.40 and 0.75 µcal/cm² s (17 and 31 mW/m²) for the heat flow beneath an old stable continent. The computed range of geotherms for an equilibrium ocean overlaps the range of stable continental geotherms below a depth of 1...

Heat flow and lithospheric thermal regime in the Northeast German Basin

“…However, the largest of such potential compositional anomalies in the Pritzwalk area unfortunately is devoid of q s observations. Thus it cannot be verified by the present data whether a thick complex of mafic rock emplaced at mid-crustal level above a thick lower crust (Franke et al 1996;Kuder, 2002) The high average q s in the NEGB of 77 mW m -2 correlates with the heat flow of provinces younger than 250 Ma (Sclater et al, 1980;Sclater et al, 1981) and is in contrast to values from older, tectonically stable provinces (50 mW m -2 ). The range of q s in the NEGB is similar to observations made farther east, in the western part of PB ( In the NEGB models, an increase of crustal A on the expense of q m to accommodate the high q s seems unjustified.…”

Geothermal heating and its influence on the meridional overturning circulation

“…Ocean crust that is older than about 50-70 million years does not produce significant hydrothermal circulations [Stein et al, 1995], yet continued cooling and radiogenic decay maintain a background heat flux of 38-46 mW m -2 [Sclater et al, 1980]. What is perhaps most notable from a thermodynamic perspective is the division of heat flux into the ocean.…”

“…Approximately 70% of this heat flux is absorbed into the abyssal oceans and marginal basins [Sclater et al, 1980]. Prior work has argued that both local hot spots (forming rising plumes) along the mid-ocean ridge axes [e.g., Stommel, 1982] and the more pervasive diffusive heating away from the ridge systems [e.g., Thompson and Johnson, 1996] play important roles in the abyssal circulation.…”

Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere

“…Oceanic heat flow can be explained by these models if hydrothermal activity at the ridge is taken into account (6); recently it has been demonstrated that the short wavelength change in geoid elevation over ridges predicted by these simple models is also readily observed (7)(8)(9).…”