Impacto do efeito blanketing na história térmica de bacias sedimentares: modelos sintéticos e estudo de caso na Bacia de Santos

Abstract

The blanketing effect is a effect of thermal insulation related to the deposition of cold sediments in a sedimentary basin that may affect its basement heat flow (BHF). We explored parameters that impact the magnitude of that effect through 1D simulations of synthetic and real case models from Santos Basin. The goal was to evaluate the role of lithospheric stretching (β), thermal conductivity, radiogenic heat generation, sedimentation rate, and sediment thicknesses of the pre-salt, salt, and post-salt packages in the magnitude of the blanketing effect. To better access the blanketing effect in the rift and post-rift phases, the results were compared to those calculated using 1D thermomechanical models without the blanketing effect. We observe that: (1) the BHF at the end of the rift stage decreases 22% and 32% if β is, respectively, 2 and 6, considering a sedimentary thickness of 5.1 km; (2) about 110 Myr after the end of the rift phase, BHF is always lower than the prerift BHF; (3) in the proximal area of Santos Basin, with high sedimentation rates (∼ 150 m/Ma), and pre- and post-salt sedimentary thicknesses of, respectively, 3,5 km and 4 km, the BHF decreases 36% compared to models calculated ignoring the blanketing effect; (4) in the distal Santos Basin, with pre- and post-salt thicknesses ≤ 1,5 km and salt layer ≥ 3 km-thick, the blanketing effect is insignificant. We conclude that the magnitude of the blanketing effect in the BHF should be taking into account in quantitative studies of areas with sedimentary thickness ≥ 3 km, thermal conductivity ≤ 3,5 W/m/K, and sedimentation rates ≥ 150 m/Ma. Thus, in areas with thin rift section and thick salt layer, one could use thermomechanical models. However, we suggest that the blanketing effect should be considered when evaluating areas similar to the proximal area of Santos Basin.