HIGH-PRESSURE GRANULITES FROM THE SUDETES (SOUTH-WEST POLAND) - EVIDENCE OF CRUSTAL SUBDUCTION AND COLLISIONAL THICKENING IN THE VARISCAN BELT

Two high-grade gneissic complexes of the Western Sudetes, the Gory Sow ie Block and the Snieznik area complex, contain small, predominantly f elsic granulitic inliers with minor Cpx-bearing intercalations. The P- T conditions of the granulite facies events and of the subsequent re-e quilibration are estimated using the ternary feldspar thermometer and the Geo-Calc computer program (version TWQ, Jan 92). In the Gory Sowie granulites, the peak granulitic event occurred at c. 18-20 kbar and 9 00 degrees C, and the late decompressive re-equilibration within a ran ge of 4-10 kbar and temperatures decreasing to 600 700 degrees C. The latter event is thought to have coincided with the main metamorphic ph ase in the surrounding gneisses. The PT estimates are more scattered i n the Snieznik granulites, but the peak conditions for the granulitic event are estimated at pressure over 22 kbar (possibly around 30 kbar) and temperature exceeding 900 degrees C. The analysed samples from th e Snieznik area bear no significant evidence of lower-pressure re-equi libration. Integrating the thermobarometric data and some age constrai nts indicates that the Gory Sowie granulites belong to the early stage 'type I' granulites of the Variscan Belt (c. 400 Ma old), which are i nterpreted as fragments of continental crustal materials subducted to mantle depths in the earliest stages of the Variscan orogeny. The Snie znik granulites are more problematic: they may belong to a 'younger hi gh-P suite' (c. 350 Ma old), widespread in the southern and eastern pa rts of the Bohemian Massif, and possibly related to the climax of the Variscan continent-continent collision.