Constraints on the origin of gabbroic rocks from the Moldanubian-Moravian units boundary (Bohemian Massif, Czech Republic and Austria)
Abstract
Gabbroic bodies from the Moldanubian Monotonous Group (Maříř) and the Moravian Vratěnín Unit, often showing retrogressive recrystallization at their margins in the amphibolite-facies grade, have norite, gabbronorite, gabbro and hornblendite compositions. Gabbros with preserved coronitic textures are limited to the Vratěnín Unit.
The estimated equilibration temperatures derived from plagioclase–amphibole pairs and orthopyroxene Ca contents calculated for pressures 5–10 kbar overlap are 680–850 °C. Gabbroic rocks from Maříž should represent an underplated, partly layered cumulate body of continental tholeiite composition, strongly influenced by crustal contamination.
In contrast, gabbroic bodies from the Vratěnín Unit, having a close spatial relationship to the surrounding garnet amphibolites, were emplaced into a lithologically variable passive margin sequence probably during the Cadomian extension.