Model calculations on intrusive cooling and related coalification of the Peel-Erkelenz coalfield (The Netherlands and Germany)

Abstract

An analytical solution of the simplified heat equation was calculated and applied to a 3D model of the intrusion below the Peel-Erkelenz coalfield. The calculated thermal history was converted to coal ranks with an empirical integral expression. Using a least squares fit of observed coal rank data, an initial temperature of (800 + 100) °C for the intrusion was obtained. Calculated vertical coal rank gradients are comparable with those observed in the Ibbenbüren coalfield (Bramsche intrusion, FRG). A detailed 2D finite difference calculation, using the complete heat equation on a 5-layer section in the area, confirmed the analytical results. It also proved that: 1) effects of radiogenic heat production are negligible compared to cooling magma effects; 2) if the coal is remote from the magma, latent heat effects can be simplified by adding 300 °C to the initial intrusion temperature; 3) lateral and vertical variations in rock properties have negligible influence on coalification compared to cooling magma effects; a homogeneous model is therefore a good approximation.