Hornblende thermobarometry of granitoids from the Central Odenwald (Germany) and their implications for the geotectonic development of the Odenwald

The three major units of the Bergstrasser Odenwald (Frankenstein Complex, Flasergranitoid Zone and southern Bergstrasser Odenwald) are, according to literature, separated by two major shear zones. The aim of the present paper is to evaluate the importance of these sutures by comparing new hornblende geothermobarometry data from five plutons of the Flasergranitoid Zone with published P-T data from the entire Bergstrasser Odenwald. Furthermore radiometric, geochemical and structural data from the literature were also used for this purpose. Temperatures were calculated with the amphibole-plagioclase thermometer and range from 600 to 800 degreesC. Determinations of the intrusion depth, using the Al-in-hornblende barometer show that most plutons intruded at pressures ranging from about 4 to 6 kbar (13 to 20 km). These combined data do not allow to postulate a major suture zone between the Flasergranitoid Zone and the southern Bergstrasser Odenwald, while comparison of similar data from the Flasergranitoid Zone and the Frankenstein Complex verify the importance of this shear zone. Moreover, our P-T data show that the high temperature - low pressure metamorphism in the Bergstrasser Odenwald can also be interpreted as contact metamorphism and not necessarily as regional metamorphism.