Depth of intrusion and thermal modeling of the Falkenberg granite (Oberpfalz, Germany)

Abstract

The Late Carboniferous Falkenberg granite, exposed 2 km to the east of the German Continental Deep Drilling (KTB) drill site, has solidified at a depth of approximately 9–12 km. The initial temperature of the intrusion was 780–800 °C. The shape of the pluton is approximately that of a horizontal plate with an assumed original thickness of approximately 9 km, 3 km of which having now been removed by erosion. The results of simple one-dimensional thermal modeling, based on conductive heat transfer, suggest cooling to 400 and 350 °C over approximately 6 and 15 m.y., respectively. With respect to the cooling ages of micas, this suggests that the intrusion is somewhat older than previously assumed. The lack of thermal influence in the nearby crustal section recovered by KTB, compared with the width of the contact aureole inferred from the model, is explained by considerable convergence between contact and drilling site. The initial (synemplacement) distance between the granite/ wall-rock contact and the KTB location was at least twice the recent value. This is consistent with Mesozoic crustal shortening, which has resulted in the antiformal stack geometry of the supracrustal slices drilled by KTB.