Provenance of the Carboniferous Hochwipfel Formation (Karawanken Mountains, Austria/Slovenia) - Geochemistry versus petrography

This study focuses on the Carboniferous sediments of the Karawanken Mountains (Austria/Slovenia) to identify possible source areas and their geotectonic setting. Provenance analyses have been applied using petrographical and geochemical approaches what also lead to an evaluation of the used methods. Within the Hochwipfel Formation five stratigraphic related petrofacies groups can be defined using the sandstone component inventory. Homogenous provenance results based on major element and trace element data suggest an active continental margin/continental island arc with probably an intraplate signature. Provenance analyses of light minerals point to source areas with basement rocks (mainly metamorphic), arc material and sedimentary rocks. In combination, the rapid and highly variable change of provenance signatures within the stratigraphic succession of the petrofacies types excludes a single provenance in the western part of the Karawanken Mountains. Additionally, changes in composition of the individual petrofacies groups correlate with the stratigraphy in the eastern part. Varying contents of garnet, chromite, hornblende and epidote, within the sedimentary succession of the Hochwipfel sandstones, can partly be attributed to geodynamical changes in the hinterland. The chemical compositions of garnets, tourmalines, and chromites, confirm the results of both geochemistry and sediment petrography. In a quantitative approach based on petrography we can see an equal mixture of all source areas, whereas quantification with a geochemical approach results in c. 11% of material that can be attributed to a passive continental margin source, 28 to 37% to an active continental margin, c. 44% to a magmatic arc setting and 16 to 19% to an oceanic within-plate source area. The resulting model for the geodynamical setting of the Hochwipfel basin during the Late Palaeozoic can be best explained by a forearc basin in the eastern part and various pull-apart basins in the western part, connected through bypasses, at the continental margin of Gondwana and the Palaeotethys. As an additional outcome this study clarifies, that geochemically derived provenance results, based on bulk-rock and mineral composition, recognize best complex geodynamical settings and a mixture of sources since they incorporate best the provenance significant lithic components. On the other hand it points out that an application of additional petrological approaches does not necessarily lead to further information and an elimination of errors but could be essential to define general information of the investigated stratigraphy, like the correlation of deposits with stratigraphy (petrofacies groups).