Quantifying the late-to post-Variscan pervasive heat flow, central Netherlands, Southern Permian Basin

The Southern Permian Basin is marked by significant Latest Carboniferous-Early Permian magmatism attributed to mantle plume emplacement. This intense magmatic activity is commonly assumed to have impacted the heat flow in this area. In the central Netherlands a large number of wells show evidence of magmatic activity dated as Permo-Carboniferous. In addition, high maturity values have been measured for the Carboniferous and below. Theoretical models for tectonic heat flow and maturity evolution presented in this paper show that mantle upwelling, underplating, and intrusions have a significant effect on maturity-depth trends. Tectonic modelling of five selected wells shows that tectonic subsidence and exhumation can be correlated with a significant heat flow pulse at Latest Carboniferous-Early Permian time. This could well explain the widespread elevated maturity/depth gradient in Carboniferous rocks. Quantitative assessment of heat flow, based on a model of mantle plume emplacement, shows that mantle upwelling and underplating at the base of the crust, proposed by previous studies, provides insufficient heat flow to explain strongly elevated maturity-depth trends. In contrast, widespread Permo-Carboniferous calc-alkaline magmatism at shallow crustal levels provides a mechanism for elevated heat flow with a regional impact, consistent with observed high maturity-depth trends. The model and maturity data demonstrate that elevated maturity at shallow burial-depth levels of 500–1000 m is probably sited in the gas window during a heat pulse, occurring at Late Carboniferous times