3:30 PM - 4:30 PM
[S26-P-03] Indications of “hot belts" along passive continental margin of Brazil
Analysis of geothermal data for the coastal sedimentary basins of eastern Brazil has revealed the existence of an anomalous high heat flow belt along its passive continental margin. The main characteristics of this anomaly are the geothermal gradients in excess of 30oC/km and heat flow greater than 70mW/m2. It is confined between zones of relatively low to normal heat flow in the adjacent continental regions to the west and stable oceanic regions to the east. The width of the belt is somewhat variable, but most of it falls within the range of 100 to 300 km. It is relatively large in the southern (in the basins of Pelotas, Santos and Campos) and northern (basins of Potiguar and Ceara) parts, when compared with those in the central parts (basins of South Bahia, Sergipe and Alagoas). The characteristics of heat flow anomalies appear to be compatible with those produced by thermal sources at shallow depths in the upper crust. Seismicity within the belt is relatively weak, with focal depths less than 10km for most of the events. Such observations imply that “tectonic bonding" between continental and oceanic segments is relatively weak. Hence, it is proposed that “passive" continental margins like that of Brazil be considered as constituting a type of plate boundary that is aseismic at sub crustal levels, but allows for escape of significant amounts of earth's internal heat at shallow depths.