EVIDENCE OF GLAUCOPHANE-SCHIST FACIES METAMORPHISM IN THE EAST KARKONOSZE COMPLEX, WEST-SUDETES, POLAND

In the East Karkonosze complex (Karkonosze = Riesengebirge), which occ urs at the northern margin of the Bohemian massif, rocks of the glauco phane-schist facies and transitions between the glaucophane-schist fac ies, greenschist facies and epidote-amphibolite facies are present. Th ey belong to the Leszczyniec Volcanic Formation (LVF) of Cambrian/Ordo vician age and to the mainly metasedimentary Czarnow Schist Formation (CSF) of Ordovician/Silurian age. Similar high-pressure, low-temperatu re rocks occur in the southern Karkonosze and in the Kaczawa Mountains within metavolcanic formations of approximately the same age. Petrogr aphic and electron probe studies show complex relationships between mi nerals including chemical zoning. In the East Karkonosze three stages of metamorphism pre-dating contact metamorphism by late Variscan (lowe rmost Upper Carboniferous) granite intrusion were distinguished [stage 1: ocean floor, amphibolite facies (observed only in part of the LVF) ; stage 2: high-pressure, low-temperature, variably glaucophane-schist facies, high-pressure greenschist facies and epidote-amphibolite faci es; stage 3: medium-pressure greenschist facies accompanied by strong deformations] . Glaucophane-schist facies rocks formed in stage 2 surv ived the later stages of metamorphism only in the southern part of Eas t Karkonosze, i. e. in Lasocki Range and Rychory. Using the Maruyama e t al. (1986) geobarometer the glaucophane-bearing rocks formed at 6.5- 7 Kb, those with crossite at 5-6 Kb and rocks with magnesioriebeckite/ riebeckite at 4-5 Kb. Other estimates for glaucophane-bearing rocks gi ve somewhat higher values of pressure, i. e. 7-12 Kb at temperatures b etween 300 and 530 degrees C. The highest temperatures are recorded in the glaucophane- and garnet-bearing rocks. Stilpnomelane may occur in all of these rocks. The subduction/obduction episode responsible for this high-pressure, low-temperature metamorphism is considered to have taken place in the early Variscan, although no geochronology is yet a vailable to confirm this.