Thermometrically inferred cooling rates from the Plattengneis, Koralm region, Eastern Alps

Abstract

Closure of FeMg exchange between garnet and biotite is used to estimate cooling rates from the Koralm region of the Austro-Alpine nappe complex east of the Tauern window in the Eastern Alps. Maximum cooling rates for a 700 m thick mylonitic shear zone, the Plattengneis, are at least an order of magnitude higher than those of surrounding country rocks. The cooling rate history inferred for the Plattengneis suggests exponentially decreasing cooling rates, whilst the cooling history of the surrounding country rocks is inferred to involve an approximately constant cooling rate. The fast cooling rates in the shear zone are interpreted as evidence for an additional energy input from an internal he..