Temperature profile in the continental lithosphere and in the mantle beneath a continent
To study the structure and composition of the upper mantle as well as to determine its physical properties, it is necessary to know the temperature distribution in it. In studies of the temperature field during the subduction, it is necessary to know the temperature boundary conditions in the upper mantle at the continental limb of the subduction zone. To find the temperature distribution in the upper mantle, it is necessary to know the temperature conditions at the upper - lower mantle boundary. These conditions can result from the analysis of heat transfer in the lower mantle. The temperature distribution in the continental lithosphere is obtained in the approximation of conductive heat transfer with internal heat sources in the crustal layer. The distribution of radioactive heat release through the thickness of the crustal layer is approximated by an exponential law. The temperature distribution through the thickness of the continent away from the subduction zone is compared with the temperature conditions of Northern Lesotho lherzolites. The latter agree closely with the calculated temperature profile. A three-layered structure of the upper mantle in the continental limb of the subduction zone is considered. The upper layer is represented by the continental lithosphere. The asthenospheric layer underlies the lithosphere extending to a depth of 410 km. The layer C is below the asthenosphere. Such a three-layer structure is obtained on the basis of the density and seismic velocity distribution in the Earth's mantle (PREM). The lithospheric mantle is highly viscous, its kinematic viscosity is г ® 108-1019 m2/s. The kinematic viscosity of the asthenospheric layer (Га ® 1014 m2/s) was estimated earlier on the basis of our experimental and theoretical modeling. In the present paper the kinematic viscosity of layer C (гс ® 4 x 1015 m2/s) is estimated. The analysis of heat transfer in the lithosphere is carried out in the approximation of conductive heat transfer (the kinematic viscosity is гл to). The analysis of heat transfer in the asthenosphere and the layer C is performed in the approximation of free-convective heat transfer. The asthenospheric layer and the layer C are separated by the "olivine-wadsleyite" phase transition. The temperature distribution in the asthenospheric layer and the layer C is obtained on the basis of experimental data on convective heat transfer in the horizontal liquid layer heated from below and cooled from above. The temperature distribution in the lower mantle was based on the results of experimental modeling of free-convection flows in the horizontal layer heated from below for the Rayleigh number Ra = 106-107 i.e., for turbulent regime of free convection.
Keywords
continental lithosphere,
asthenosphere,
lower mantle,
experimental and theoretical modeling,
free-convective flows,
horizontal liquid layer,
temperature distributionAuthors
| Kirdyashkin Anatoly G. | Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences | agk@igm.nsc.ru |
| Kirdyashkin Alexey A. | Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences | aak@igm.nsc.ru |
Всего: 2
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