Thermal evolution of high-pressure metamorphic rocks in the Alps

Abstract

There are two major and currently unresolved issues in Alpine geology concerning the metamorphic evolution of the rocks in the internal zones of the Alps. First, rocks showing evidence for geologically young, high-pressure to very high-pressure metamorphism are now exposed at the Earth's surface, implying exhumation from depths as much as lOO km in a belt less than 250 km wide. Secondly, these high-pressure rocks, in places, show evidence for significant re-heating during their ascent, a phenomenon known in the central Alps as the Lepontine metamorphism. This thesis addresses geological evidence for these two features in rocks from the Alps, and investigates possible causes. This is done by a combination of detailed field-based studies involving reconstruction of pressure-temperature-time (PTt) trajectories of pertinent rocks, and numerical modelling of processes that may explain a re-heating during exhumation. The PTt paths serve as constraints on numerical modelling results, and allow testing of contending hypotheses regarding possible causes for heating during exhumation of the high-pressure rocks in the Alps.