EXHUMATION OF ECLOGITES - INSIGHTS FROM DEPTH-TIME PATH-ANALYSIS

Literature data on geochronology and pressure-temperature estimates ha ve been used to assess the depth-time paths for high-pressure units in the Alps and the Variscan belt. These depth-time paths consistently s how that exhumation rates decrease through time. The first stages of t he exhumation are rapid (>1 mm yr(-1)) and last less than a few millio n to a few tens of million years. In contrast, the final 10-20 km asce nt to the surface is at least one order of magnitude slower. For the d eepest and most important part of the exhumation trajectory, the chron ology of the retrogressive metamorphism excludes gravitational collaps e as the major driving force. Material balance and structural argument s also exclude isostatically assisted erosion processes. Prism dynamic s and tectonically assisted erosion are the most likely mechanisms acc ounting for the kinetics of exhumation. Isostasy-assisted erosion and shallow-level extension are nevertheless required to eventually bring the high-pressure rocks to exposure.