Transition from High-/ultrahigh-pressure Metamorphic Rocks to the Continental Crust

Abstract

Processes of the granulite facies overprinting on high-pressure (HP) and ultrahigh-pressure (UHP) rocks were considered by comparing the model and actual P-T paths. The model P-T paths based on the thermal structures below the continent-continent collision zone predict that the granulite facies overprinting on the HP and UHP rocks can occur in following three cases. 1) Exhumation at a moderate rate resulting in moderate heating during decompression, which forms a clockwise P-T path. 2) Infinitely fast exhumation of relatively high-T (>700°C) HP/UHP rocks. 3) Isobaric heating at lower-crust depths. Several HP rocks in the western gneiss region and the Bohemian massif recorded paths 1) and 2) and UHP rocks in these areas recorded the path 2). There is only one report of the path 3) in the Bohemian massif. P-T paths of the granulitized coesite-eclogite in eastern China is still under discussion. In the regional gneiss region, granulite facies overprinting on the HP/UHP rocks, i.e., a transition from HP/UHP rocks to the continental crustal material, seems to be not a rare phenomenon.