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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS017 Oral Presentation 2381
Heat flow and thermal models of a hot craton in the South American
continental lithosphere
Prof. Valiya Hamza
Geofsica Observatrio Nacional-ON, Rio de Janeiro, Brazil IASPEI
A detailed analysis of geothermal data from the highland area of eastern Brazil has been carried out as
part of an attempt to understand regional variations in geothermal gradients and heat flow across the
So Francisco craton and the neighboring metamorphic fold belts. The database employed includes
results of geothermal measurements at 53 localities. The results indicate that the craton and the
adjacent metamorphic fold belts are characterized by geothermal gradients in the range of 8 to
270C/km, with a mean of 14.3 0.8C/km. The estimated heat flow values are found to fall in the range of
30 to 70mW/m2, with low values in the northern parts of the craton. Superimposed on this regional
trend are the occurrences of several isolated small-scale anomalies with thermal gradients of greater
than 40C/km (with corresponding heat flow values in excess of 80mW/m2). These are in general
associated with over-thrust terrains on the eastern and western border of the craton. There are
indications that lateral heat transfer by subsurface fluid circulation is responsible for the occurrence of
such anomalous thermal belts. Crustal temperatures were calculated using based on a procedure that
makes simultaneous use of the Kirchoff and Generalized Integral Transforms. The thermal models take
into consideration variation of thermal conductivity with temperature as well as change of radiogenic
heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates
of radiogenic heat production in crustal layers. The results point to temperature variations of up to
250oC at the Moho depth, between the cold northern and hot sothern parts of the craton. There are
indications that such differences are responsible for the contrasting styles of deformation patterns in the
metamorphic fold belts. 1. JSS017 2. Lithosphere thermal state and geodynamic processes: from
measurements to models 3. So Francisco Craton, Thermal Models 4. Valiya Hamza, Observatrio
Nacional, Rua General Jos Cristino, 77, Rio de Janeiro Brazil, Tel. +55 21 2580 7081, Fax +5 21 2560
7081, e-mail: hamza@on.br 5. O 6. PC 7. NO 8. Carlos Alexandrino: NO, Valiya Hamza: YES 9. NONE
Keywords: hotcraton, thermalmodels, easternbrazil