ECLOGITE MESO-FABRIC AND MICROFABRIC - IMPLICATIONS FOR THE BURIAL AND EXHUMATION HISTORY OF ECLOGITES IN THE TAUERN WINDOW (EASTERN ALPS) FROM P-T-D PATHS

The Eclogite Zone of the central-southern Tauern Window comprises eclo gites and associated high-pressure metasediments that are intercalated between Penninic basement units in the foot-wall and an imbricate sta ck in the hanging-wall. This nappe stack consists of continental basem ent units, cover sequences of a distal continental slope, and the main part of the ophiolitic Glockner Nappe. Textures and microfabrics of e clogites from the central-southern Tauern Window allow the establishme nt of the eclogitic and post-eclogitic deformation histories from buri al by subduction to subsequent exhumation. The metamorphic evolution o f the eclogites is documented by: (1) initial greenschist to blueschis t facies; (2) eclogite facies at ca. 550-630 degrees C and +/-20 kbar; (3) a second blueschist facies overprint (ca. 450 degrees C, 10-15 kb ar); and (4) exhumation to pressures of ca. 6-7 kbar at 500-550 degree s C (upper greenschist to lower amphibolite facies). An eclogitic pene trative foliation (S-1) and S-dipping stretching lineation (L-1) forme d during the final stages of subduction of the eclogite-bearing unit. The P-T evolution of the eclogites during D-1 documents the final incr ement of the prograde P-T path. Later blueschist facies metamorphism i s contemporaneous to top-to-the-N emplacement of the eclogite-bearing unit onto continental basement units within a subduction zone. We disc uss two models of eclogite emplacement. Most probably, emplacement is achieved by a thrust along the base of the eclogite-bearing unit. Alte rnatively, the P-T path of the eclogite facies rocks suggests an empla cement model similar to corner flow. Subsequent to eclogite and nappe emplacement, the nappe stack is entirely affected by a penetrative def ormation (D-2) that resulted in the development of a mylonitic foliati on (S-2) and an E-W-oriented stretching lineation (L-2) within lower a mphibolite to upper greenschist facies. This deformation is related to a crustal-scale detachment zone, that formed during the exhumation of the Penninic units. (C) 1998 Elsevier Science B.V. All rights reserve d.