Obliteration of thermal springs by groundwater flows in sedimentary basins of Brazil

Abstract

Analysis of geothermal and hydrogeologic characteristics of Paleozoic interior basins of Brazil has identified an association between the geographic distribution of thermal springs and areas of occurrences of groundwater flow. Specifically, thermal springs are found to be absent in regions inferred to have lateral flows of groundwater. This trend is evident in the basins of the Amazon region, in the central parts of the Parnaiba basin and in the west-central parts of the Parana basin. Model studies help to elucidate mutual exclusion of regions of thermal springs and sub-horizontal flows of groundwater. Numerical simulations indicate that groundwater flows with velocities ≥ 1 cm/year are capable of masking the occurrence of thermal anomalies. Also, down flow through distributed recharge zones can lead to development of large zones of relatively low temperature. The observational data sets of temperature gradients and Peclet numbers have been employed outlining advection-convection domains of subsurface strata in the sedimentary basins of the Amazon region, Parnaiba and Parana. Results obtained indicate that thermal buoyancy forces are incapable of overcoming advective flows in basins of the Amazon region. Similar conditions are also found to prevail in the central parts of the Parnaiba and Parana basins.