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THERMAL ASPECTS OF LITHOSPHERIC DEFORMATION |
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The continental geotherm, i.e. the distribution of temperature with depth, is a function of: i) the rate at which heat is produced within the lithosphere, and ii) the rate at which heat is exchanged within the continental lithosphere as well as between the lithosphere an its surrounding. Temperature is a fundamental parameter as it impacts on every physical rocks' properties (density, rheology, etc) and therefore on the mechanical properties of the lithosphere.
We first review here the parameters involved in the mathematical definition of the continental geotherm. In a second part we will discuss the impact on the geotherm of a number of lithospheric deformation scenari.
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| Temperature and Heat |
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There are two types of continental geotherm: Steady state geotherms are those for which the temperature at any given depth does not change through time. In most cases, including in stable cratonic areas, geotherms are transient which means that at any given depth the temperature varies through time.
The temperature (degree of hotness or coldest) of a small volume of rock in the lithosphere varies if heat (a form of energy= kinetic energy) is gained or lost. The relationship that gives the variation of temperature as a function of a variation of heat is: dT=dQ/(Cp.m), with Cp the heat capacity, and m the mass. The main causes changing the amount of heat contained in small volume or rock in the lithosphere are:
- Heat conduction (transfer of kinetic energy between molecules or atoms)
- Heat advection (replacement of a volume at temperature T1 with an equivalent volume at temparature T2)
- Heat production (radiogenic heat produced by radioactive elements, viscous heating, exothermic reactions)
- Heat consumption (endothermic reactions)
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The rate at which temperature change depends on the rate at which heat is gained or lost. |
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