Relics of high-pressure metamorphism from the Grossglockner region, Hohe Tauern, Austria; paragenetic evolution and PT-paths of retrogressed eclogites
Relics of high-pressure metamorphism from the Grossglockner region, Hohe Tauern, Austria; paragenetic evolution and PT-paths of retrogressed eclogites
European Journal of Mineralogy (February 2001) 13 (1): 67-86
- Alps
- amphibole group
- Austria
- Central Europe
- chain silicates
- clinoamphibole
- Eastern Alps
- eclogite
- Europe
- garnet group
- geologic barometry
- geologic thermometry
- glaucophane
- high pressure
- Hohe Tauern
- metamorphic rocks
- metamorphism
- nesosilicates
- orthosilicates
- P-T conditions
- pressure
- regional metamorphism
- retrograde metamorphism
- silicates
Retrogressed eclogites occur embedded in mainly calcareous mica schists and greenschists of the Upper Schieferhulle. A four stage metamorphic evolution has been established. Stage I: relics of early pre-eclogite facies events (chlorite, actinolite, plagioclase and glaucophane, paragonite, clinozoisite) are preserved mainly in the cores of garnets. A peak metamorphic paragenesis (stage II) of garnet, omphacite, paragonite, (clino)zoisite, quartz and rutile + or - dolomite records conditions of approximately 17 kbar and 570 degrees C. In several instances, growth of coarse-grained barroisitic to actinolitic amphibole occurred during uplift, apparently still within the eclogite facies (stage III). The final emplacement in the present tectonic setting and co-metamorphism with the surrounding metasediments (stage IV) occurred at 5-6 kbar and 500-530 degrees C, causing severe hydration and retrograde alteration (symplectite formation), and transforming most of the eclogite bodies into garnet amphibolites and even greenschists. It is suggested that a major tectonic slice was injected into the evolving Pennine nappe stack during underthrusting of the Penninic units beneath the Austroalpine.