DEPTH OF INTRUSION AND THERMAL MODELING OF THE FALKENBERG GRANITE (OBERPFALZ, GERMANY)

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 i ntrusion was 780-800 degrees C. The shape of the pluton is approximate ly that of a horizontal plate with an assumed original thickness of ap proximately 9 km, 3 km of which having now been removed by erosion. Th e results of simple one-dimensional thermal modeling, based on conduct ive heat transfer, suggest cooling to 400 and 350 degrees C over appro ximately 6 and 15 m.y., respectively. With respect to the cooling ages of micas, this suggests that the intrusion is somewhat older than pre viously assumed. The lack of thermal influence in the nearby crustal s ection recovered by KTB, compared with the width of the contact aureol e inferred from the model, is explained by considerable convergence be tween contact and drilling site. The initial (synemplacement) distance between the granite/wall-rock contact and the KTB location was at lea st twice the recent value. This is consistent with Mesozoic crustal sh ortening, which has resulted in the antiformal stack geometry of the s upracrustal slices drilled by KTB.