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Vol.3 , No. 6, Publication Date: Oct. 29, 2016, Page: 61-72
, it is based on analytical solution to the standard heat conduction problem in stratified media, coupled with empirical relations between seismic velocities and temperatures at the crust-mantle interphase. Iterative trial and error methods are employed in establishing successful coupling. This technique allows estimation of crustal temperatures and mantle heat flow with lesser uncertainty than has so far been possible. The results obtained are relatively free of errors arising from the petrological complexities of the upper crust and are in broad agreement with crustal temperatures derived by conventional methods. Examples of the use of this method has been illustrated by calculating basal temperatures and crustal geotherms for four distinct segments of the Tocantins Structural Province in Brazil, namely the Araguaia Belt, Goiás Massif, Fold and Thrust Zones and Regions of sedimentary cover adjacent to the Sao Francisco Craton. The basal temperatures at the crust-mantle interphase in this province are found to fall in the interval of 760 to 1034°C, while the overall crustal thermal gradients are in the range of 16 to 20°C/km. Calculations of mantle heat flow, as per STM, indicate values in the range of 37 to 51mW/m2. The results reveal that deep crustal heat flow is relatively high in the Araguaia Belt and Goiás Massif, when compared with that in regions of Thrust and Fold Belts and sediment cover over São Francisco craton. Such second order changes in deep-level heat flow have not so far been detected in earlier studies based on conventional geothermal mapping. Use of the newly proposed method (STM) also opens up the possibility of setting up a global reference framework of deep geotherms in different tectonic settings, based on results of crustal seismic surveys.&picture=http://www.aascit.org/aascit/decorators/img/journal/899.jpg)
| [1] | Alexandrino C. H., Federal University of the Jequitinhonha and Mucuri Valleys, Teófilo Otoni (MG), Brazil. |
| [2] | Hamza V. M., National Observatory, Rio de Janeiro (RJ), Brazil. |
An improved method for calculating crustal geotherms in stable continental crust is proposed, based on integrated use of data acquired in crustal seismic and heat flow studies. Designated as seismo-thermal method (STM), it is based on analytical solution to the standard heat conduction problem in stratified media, coupled with empirical relations between seismic velocities and temperatures at the crust-mantle interphase. Iterative trial and error methods are employed in establishing successful coupling. This technique allows estimation of crustal temperatures and mantle heat flow with lesser uncertainty than has so far been possible. The results obtained are relatively free of errors arising from the petrological complexities of the upper crust and are in broad agreement with crustal temperatures derived by conventional methods. Examples of the use of this method has been illustrated by calculating basal temperatures and crustal geotherms for four distinct segments of the Tocantins Structural Province in Brazil, namely the Araguaia Belt, Goiás Massif, Fold and Thrust Zones and Regions of sedimentary cover adjacent to the Sao Francisco Craton. The basal temperatures at the crust-mantle interphase in this province are found to fall in the interval of 760 to 1034°C, while the overall crustal thermal gradients are in the range of 16 to 20°C/km. Calculations of mantle heat flow, as per STM, indicate values in the range of 37 to 51mW/m2. The results reveal that deep crustal heat flow is relatively high in the Araguaia Belt and Goiás Massif, when compared with that in regions of Thrust and Fold Belts and sediment cover over São Francisco craton. Such second order changes in deep-level heat flow have not so far been detected in earlier studies based on conventional geothermal mapping. Use of the newly proposed method (STM) also opens up the possibility of setting up a global reference framework of deep geotherms in different tectonic settings, based on results of crustal seismic surveys.
Keywords
Crustal Geotherms, Seismo-thermal Method, Tocantins Structural Province, Seismic Velocities, Mantle Heat Flow, Global Framework for Geotherms
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