MINERALOGY AND PETROLOGY OF MAFIC BLUESCHISTS FROM THE RYCHORY MTS CRYSTALLINE COMPLEX (WEST SUDETES, BOHEMIAN MASSIF)

Mafic blueschists of the Radcice Group (the Rychory Mts. crystalline c omplex, West Sudetes) are composed of Na-amphibole (glaucophane, ferro glaucophane and crossite), epidote, albite, quartz, chlorite, phengite and rare garnet. Rectangular muscovite-epidote aggregates are interpr eted as pseudomorphs replacing lawsonite. In the Middle to Late Devoni an these mafic rocks experienced metamorphism of the blueschist facies identical to that of the Sanbagawa schists. Based on mineral assembla ges, the metamorphic conditions were T = 300 degrees-500 degrees C and P = 0.7-1.0 GPa. The HP-LT metamorphism was followed by retrogression under greenschist facies conditions. The protolith of the mafic blues chists were basic igneous rocks analogous in major and trace element c omposition to tholeiitic and/or transitional ocean-floor basalts; the age of their origin can be dated to the Cambro-Ordovician. The Rychory Mts. metabasites, showing blueschist metamorphic grade as well as a c hemical composition related to ocean-floor basalt, suggest a possible position of a Variscan suture between formerly independent terranes, a long which oceanic lithosphere was subducted.