An updated analysis of geothermal data from the highland area of eastern Brazil has been carried out and the characteristics of regional variations in geothermal gradients and heat flow examined. The database employed includes results of geothermal measurements at 45 localities. The results indicate that the Salvador craton and the adjacent metamorphic fold belts northeastern parts of the study area are characterized by geothermal gradients in the range of 6-17°C/km. The estimated heat flow values fall in the range of 28-53 mW/m 2 , with low values in the cratonic area relative to the fold belts. On the other hand, the São Francisco craton and the intracratonic São Francisco sedimentary basin in the southwestern parts are characterized by relatively higher gradient values, in the range of 14-42°C/km, with the corresponding heat flow values falling in the range of 36-89 mW/m 2 . Maps of regional variations indicate that high heat flow anomaly in the São Francisco craton is limited to areas of sedimentary cover, to the west of the Espinhaço mountain belt. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations in heat flow. 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. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 300°C at the Moho depth, between the northern Salvador and southern São Francisco cratons. There are indications that differences in rheological properties, related to thermal field, are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts.

A magma accretion model of oceanic lithosphere is proposed and its implications for understanding its thermal field examined. The new model (designated Variable Basal Accretion-VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer is considered a space dependent variable. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling models. Another noteworthy feature of the new model is its ability to account for the main features in the thermal behavior of oceanic lithosphere. The improved fits to bathymetry have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation. Also, use of VBA model does not lead to artificial discontinuities in the temperature field of the lithosphere, as is the case with GDH (Global Depth Heat Flow) reference models. The results suggest that estimates of global heat loss need to be downsized by at least 25%.

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Data on Silica content of ground waters have been employed in obtaining estimates of heat flow for more than 500 localities, distributed over six tectonic provinces in Brazil. The procedure adopted is based on the use of an improved geo-thermometry relation for solubility of silica in ground waters. It is coupled with a revised interpretation of the empirical relation between silica content and heat flow, that allows for independent determination of the depth of circulation of ground waters. According to the results obtained mean heat flow values obtained for sedimentary areas of the late Proterozoic Sao Francisco basin and the Paleozoic Amazon basins are in the range of 45 to 47mW/m2. Similar range of heat flow values were found for the Precambrian Borborema province in the northeastern region of Brazil. Higher heat flow values of greater than 50mW/m2 were encountered for the eastern coastal area of Sergipe – Alagoas. On the other hand, Parana basin in southeast Brazil is found to have heat flow values higher than 55mW/m2. Such ranges of mean heat flow values are found to be in reasonably good agreement with those reported in earlier studies, using conventional methods. This trend is considered as indication that silica content of ground waters may be used for obtaining reliable estimates of conductive heat flow in areas where practical limitations impede use of conventional methods.

In this work we consider model formulations that allow better understandings of the relations between Darcy velocity and temperatures in coupled two-dimensional systems. The revised theoretical formulations are capable of accounting for the effects of heat transfer by fluid movements in horizontal and vertical directions. The models have been found useful in estimating the maximum and minimum depths of thermal and non-thermal waters in several geological units in Brazil. The best fitting values encountered are 1.8 to 2.7 km for the Paraná basin, 2.0 to 2.8 km for the Parnaiba basin, 1.6 to 2.3 km for the Amazon basins, 2.0 to 2.7 km for the San Francisco Province, 1.9 to 2.4 km for the Sergipe-Alagoas basins and 2.0 to 2.8 km for the Borborema Province. The models have also allowed estimation the average values of Péclet number and Darcy velocity for groundwater flows in these units. Note that higher horizontal velocities are associated with smaller depths of circulation. This is a natural consequence of the fact that in systems where horizontal velocities are high the quantities of vertical flows are less intense.

Nos quatro anos do governo Bolsonaro, vinte e cinco instituições federais de ensino sofreram intervenção. Este livro foi escrito por reitoras e reitores, vice-reitoras e vice-reitores eleitos em suas instituições e não nomeados pelo então Presidente da República. Decidimos não nos calar. Em vez de assistirmos passivamente a história passar, resolvemos registrá-la. Reafirmamos nosso compromisso com as comunidades que nos elegeram, não permitindo que esta história seja esquecida ou minimizada. Nos relatos aqui apresentados, fica clara a brutalidade da ação interventora e o oportunismo utilizado para subjugar as universidades aos interesses ideológicos e político-partidários. Ao mesmo tempo que traz uma elevada carga de sentimentos, este livro também é um convite à renovação das esperanças. É a nossa luta para que reitoras e reitores eleitos sejam, hoje e sempre, reitoras e reitores empossados. É a nossa luta para que, nunca mais, as instituições federais de ensino tenham que ser submetidas ao que estamos vivenciando. Prof. Dr. Marcel Fernando da Costa Parentoni

Crustal thermal models that incorporate thermo-barometric data have been developed for estimating depth to 1300 ºC isotherm in two xenoliths provinces: Southeast Paraguay and Andean domain, in South American Platform. Uncertainties in model results has been minimized by imposing reasonable bounds on some of the key model parameters. Considering only the best fit results it is possible to infer average values for geothermal parameters at the surface. This imply heat flow of 86 mWm-2, radiogenic heat production of 1.8 µWm-3. Besides at Moho depth: heat flow of 21 mWm-2, radiogenic heat production of 4.5x10-3 µWm-3, temperature of from Southeast Paraguay. For the Andean Domain, we have the following values for the geothermal parameters: heat flow, 72 mWm-2, radiogenic heat production, 1.0 µWm-3 in surface and heat flow of 33 mWm-2, radiogenic heat production of 2.0x10-3 µWm-3 and temperature of 785ºC in Moho depth. The heat flux estimated for the southeastern Paraguay is higher than that for the Andean domain. This result is in agreement with differences in geological ages between these sites, since the age value for Paraguayan region is approximately 20% lower than the Andean one.