Common high-pressure metamorphic history of eclogite lenses and surrounding metasediments; a case study of calc-silicate reaction zones (Erzgebirge, Germany)
Common high-pressure metamorphic history of eclogite lenses and surrounding metasediments; a case study of calc-silicate reaction zones (Erzgebirge, Germany) (in From field observation to experimental petrology and back; a special issue to honour Werner Schreyer, Walter Maresch (editor), Edward Grew (editor) and Friedrich Seifert (editor))
European Journal of Mineralogy (October 2008) 20 (5): 757-775
- amphibole group
- calc-silicate composition
- Central Europe
- chain silicates
- chemical reactions
- clinopyroxene
- clinozoisite
- eclogite
- electron probe data
- epidote group
- Erzgebirge
- Europe
- exhumation
- feldspar group
- fluorine
- framework silicates
- garnet group
- Germany
- gneisses
- halogens
- high pressure
- marbles
- metamorphic rocks
- metamorphism
- metasedimentary rocks
- mica group
- nesosilicates
- orthogneiss
- orthosilicates
- P-T-t paths
- phengite
- pressure
- prograde metamorphism
- pyroxene group
- schists
- sheet silicates
- silicates
- sorosilicates
- zoning
- Hammerunterwiesenthal Germany
- Stumpelfelsen Quarry
The Erzgebirge Dome in the Central European Variscides is a stack of crustal slices including some high- and ultrahigh-pressure rocks related to continent-continent collision. One such slice is the Mica-Schist/Eclogite Unit, in which the predominantly metasedimentary country rocks appear to record maximum metamorphic pressures of at most 11-13 kbar, whereas volumetrically minor eclogite lenses within the unit indicate pressures up to 27 kbar. In the present study, the P-T evolution of rocks found in calc-silicate reaction zones between eclogite and country rock marble near the locality Stuempelfelsen, a crag composed of eclogite near the village of Hammerunterwiesenthal, has been established via conventional geothermobarometry. A metasomatic marble-eclogite interchange can be documented for the earliest stages of prograde metamorphism. Significant amounts of fluorine infiltrated the metabasic rocks from the marbles, leading to fluorine-bearing amphibole as well as phengite, and even fluorine-rich growth zones in garnet with 0.62 wt.% F and 1.2 wt.% OH. This appears to be the first description of a F-bearing member of an almandine-grossular solid solution poor in andradite component. The P-T path of the eclogite-marble reaction zone reaches a maximum pressure of 26 kbar at 520-640 degrees C, just below the quartz-coesite transition. The exhumation path can be traced to 10 kbar and 450-600 degrees C, where it is then coincident with the published P-T paths of the mica schists and orthogneisses of the Mica-Schist/Eclogite Unit. This study indicates that the Stuempelfelsen eclogite lens and the surrounding metasedimentary country rock of the area must share a common high-pressure metamorphic history. The critical question arising for future studies is how much of the Mica-Schist/Eclogite Unit has actually "traveled the high-pressure eclogite route", and how much of it was never subducted to pressures greater than 11-13 kbar.