CONODONT COLOR ALTERATION INDEXES - PALEOTEMPERATURES AND METAMORPHISM IN THE NORTHERN CALCAREOUS ALPS - A GENERAL VIEW

The middle and eastern parts of the Northern Calcareous Alps (NCA) can be subdivided into two distinct units with a lateral boundary marked by abrupt changes in the conodont colour alteration index (CAI-values) . The first of these is a northern unit (Tirolikum) with a relatively homogeneous distribution of no or low grade conodont alteration (CAI 1 .0-2.0). The thermal overprint is thought to be relatively young and r elated to a heat flow from the Tauern crystallization. The second unit consists of the Juvavic nappe system (Juvavikum), which is distribute d along the southern rim of the NCA but also covers some of the northe rn parts of the Tirolikum. With respect to its CAI-distribution the Ju vavikum is more heterogeneous on a regional and local scale, with some local CAI-inversions. The Juvavikum additionally shows distinctly dif ferent sets of CAI-values: one with weak (CAI 1.0-1.5) and another wit h strong alteration (CAI 5.5-7.0) - at present the highest known therm al overprint measured in the NCA. The metamorphism is relatively old a s it predates the Late Jurassic - Early Cretaceous gravity tectonic em placement of the Juvavikum onto the Tirolikum. The high CAI-values of parts of the Juvavic nappe system are though to be related to tectonic burial in an accretionary wedge formed parallel to the closure of the 'Vardar' Ocean. The low CAI values of the Tirolikum apparently exclud e a direct juxtaposition of the two units at the time of metamorphism.