Thermal effects of igneous intrusions on maturity of organic matter: A possible mechanism of intrusion

This paper assesses thermal maturation of organic matter near a well-dated intrusion in the DSDP 41-368 hole near Cape Verde Rise, eastern Atlantic, and near some other intrusions from the U.K., U.S.A. and east Greenland. The traditional numerical model with instantaneous intrusion satisfactorily describes the thermal evolution and thermal maturity aureoles of igneous bodies only if the initial temperature of intrusion is close to or even lower than the solidus temperature. Calculations in this model with more real values of the intrusion temperature and with consideration of latent heat effects lead to considerable over-estimation of thermal influence of the intrusion. Models which consider formation of the intrusive body over time (as distinct from instantaneous intrusion), and especially models of emplacement of an intrusive body in the shell of relatively cool magmatic rocks, show better agreement between the computed and observed vitrinite reflectance profiles. Consideration of convective heat flow due to hydrothermal activity arising in the vicinity of the intrusion during its formation and cooling helps to explain the difference between maturation profiles above and below some sills.