Provenance of Cretaceous synorogenic sandstones in the Eastern Alps: constraints from framework petrography, heavy mineral analysis and mineral chemistry

The detrital components of Cretaceous sedimentary rocks in the Northern Carcareous Alps reflect the early Alpine geodynamic evolution of the Austroalpine microplate. Two contrasting source areas are distinguished on the base of light and heavy mineral analysis. The first source area is located at the southeastern margin of the Austroalpine and is composed of Palaeozoic sediments and metamorphic rocks, Mesozoic carbonate rocks, and ultrabasic rocks derived from the suture zone of the Vardar/Meliata Ocean. The second source area is located in the northwest in a Lower Austroalpine position near the transpressive plate margin that juxtaposes Austroalpine and Penninic units. This source area comprises Palaeozoic low-grade metamorphic rocks including high-pressure (HP) rocks, late Palaeozoic (meta)sediments, Mesozoic carbonate rocks, and ultrabasic rocks from obducted slices of Penninic oceanic crust. Chemical analyses of detrital white mica, amphibole and garnet support the discrimination between the two source areas. Tourmaline chemistry calls for a significant amount of metasedimentary rocks in the source area. Granitoid rocks and high-grade metamorphic rocks are rare. Blue amphibole, phengite, and chloritoid composition suggest the erosion of lower blueschist facies rocks in the northwestern source area. We suggest a modified model of Austroalpine Valanginian to Coniacian tectono-sedimentary evolution which is based on (1) an onset of subduction of the Penninic Ocean no earlier than Late Cretaceous, (2) deposition of the analyzed sedimentary rocks in piggyback basins, and (3) a reconstruction of provenance as proposed in this study. (C) 1999 Elsevier Science B.V. All rights reserved.