Crustal temperatures in the Variscan massif of southern Portugal: an assessment of effects of parameter variations

Abstract

Crustal geotherms are estimated for the Variscan massif of the Ossa Morena Zone and South Portuguese Zone, where average surface heat flow is 60 and 80 mW m −2, respectively. A layered crust is assumed, with heat generation rate and thermal conductivity of each layer varying within acceptable limits. Surface temperature and heat flow are used as boundary conditions, while Moho heat flow is not assigned a priori. Solutions are rejected, on the basis of geophysical evidence, if they result in Moho temperature and/or heat flow larger than 700 °C and 30 mW m −2. The accepted solutions are presented as average ±2 standard deviation geotherms. Average geotherms yield Moho temperatures of 520±100 °C in the Ossa Morena Zone, and 610±100 °C in the South Portuguese Zone. The Moho heat flow corresponding to the average geotherms is in the range 27–30 mW m −2 in both zones. The higher surface heat flow in the South Portuguese Zone is accounted for in terms of higher heat generation rate (2.9–3.2 μW m −3) in the upper crust.