KINEMATICS OF PENNINIC NAPPES (GLOCKNER NAPPE AND BASEMENT-COVER NAPPES) IN THE TAUERN WINDOW (EASTERN ALPS, AUSTRIA) DURING SUBDUCTION ANDPENNINIC-AUSTROALPINE COLLISION

The succession of deformation events within the Penninic oceanic seque nce of the Glockner Nappe and the underlying Penninic continental marg in sequences within the Tauern Window has been investigated in order t o constrain the kinematics of subduction and subsequent collision with the Austroalpine upper plate within this suture zone. Top-to-the-N- t o NE-shear (D-1) within the Penninic lower plate was contemporaneous t o, and postdated, high pressure eclogite and blueschist facies metamor phism, and predated the thermal peak of Barrovian type metamorphism wi thin the Penninic units. An eclogitic mylonitic foliation within the E clogite Zone of the southern Tauern Window was probably synchronous wi th respect to the peak pressure event or slightly postdates the pressu re peak. Emplacement of the eclogite-bearing units onto Penninic units with continental basement (Venediger Nappe Complex, VNC) occurred sub sequent to eclogite facies metamorphism. The Eclogite Zone was overrid den by a pile of basement-cover nappes (Rote Wand - Modereck Nappe) an d the Glockner Nappe which forms the main Penninic Austroalpine suture zone. The Penninic nappe pile was affected by blueschist facies metam orphism afterwards. Thus progressive top-to-the-N shear was related to internal Penninic nappe stacking driven by the subduction of Penninic continental basement (VNC), and emplacement of the ophiolitic Glockne r Nappe after consumption of the South Penninic oceanic domain. Later, top-to-the-W shear (D-2) was related to crustal thinning and decompre ssion of the Penninic lower plate including the Glockner Nappe and dev eloped at, or slightly previous to, peak thermal conditions (ca. 30 Ma ); thrusts were partly reactivated during exhumation, especially withi n the northeastern part of the Tauern Window. Top-to-the-W shear start ed at higher structural levels and is continuously transferred to deep er structural levels within the VNC. Especially within the continental basement units in the central and eastern part of the Tauern Window D -2 became penetrative, while the Penninic nappe pile including the Glo ckner Nappe was affected penetratively only in local domains within th e Tauern Window. Afterwards, the structure of the Tauern Window was hi ghly modified during exhumation and doming (D-3) An Alpine indenter in the southern central part caused the kinked shape of the window and t he rotation of several previous structures and kinematic indicators. T he entire kinematic development that is preserved in the Tauern Window is younger and, therefore, independent from the development in the Au stroalpine nappe pile that has only been transported as a rigid block over the Penninic units during the documented deformation sequence. Th e Eastern Alps are, therefore, the result of two collisional events du ring the Alpine orogenic cycle.