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Cretaceous evolution of the northwestern Dinarides as revealed by multiple sedimentary provenance indicators

In orogenic settings, where evidence of past events is often obscured by strong tectonic overprinting, dismemberment and erosion, clastic sediments represent a valuable source of information pertaining to the geological history of such regions. Synorogenic clastic formations which outcrop on the mountains and hills of northwestern Croatia document the evolution of this part of the Dinaride orogen, including the Dinaride-Alpine transitional area, a region characterized by considerable geological complexity resulting from a severe and long- lasting deformational history (Haas et al., 2000). By combining a range of provenance sensitive indicators (petrography, heavy minerals, wholerock geochemistry, microprobe analysis of individual heavy mineral grains, zircon fission track thermochronology) measured on the siliciclastic detritus of sandstones ranging in age from Early to latest Cretaceous, we aim to constrain the composition and dynamics of ophiolitic and continental source terrains being exhumed and eroded in the northwestern Dinarides and neighboring regions during the Mesozoic. The quantitative data allow comparisons to be drawn with neighboring Alpine, Tisza and other Dinaride regions. Major and trace element concentrations agree with the petrography and heavy mineral content of the studied sandstones, and confirm a very strong supply of detritus from ophiolites to the area of the NW Dinarides in the Early Cretaceous. These were harzburgitic mantle peridotites and associated cumulate rocks which developed in a supra-subduction zone setting of the Neotethys (Lužar-Oberiter et al., 2009). Fission track data of detrital zircons indicate that continental fragments which were being exhumed during the Late Jurassic-Early Cretaceous built up the source area along with the ophiolites. These units probably represent thrusted sheets of the Adria passive margin, parts of which underwent metamorphic overprint related to subduction-obduction processes in the Late Jurassic (Schmid et al, 2008). Medium grade metapelites made up a significant portion of these units, as did metamafic rocks, while high grade metasediments and granitoid rocks occurred more sporadically. Carbonate sediments also supplied significant amounts of detritus. A significant change in the fission track data is recorded in Maastrichtian sandstones compared to older samples, in that almost all of the zircons display notably younger ages. They indicate that the continental detritus which was supplied to the basins of the NW Dinarides in the latest Cretaceous derived from the erosion of newly, rapidly exhumed basement units which had undergone Eo-Alpine metamorphism either in the neighboring Eastern Alps and/or Tisza, or possibly the Dinarides themselves. Lužar-Oberiter, B., Mikes, T., von Eynatten, H. and Babić, Lj. (2009) Ophiolitic detritus in Cretaceous clastic formations of the Dinarides (NW Croatia): evidence from Cr-spinel chemistry. Int. J. Earth Sci., 98, 1097-1108. Haas, J., Mioč, P., Pamić, J., Tomljenović, B., Árkai, P., Bérczi-Makk, A., Koroknai, B., Kovács, S. and Felgenhauer, E.R. (2000) Complex structural pattern of the Alpine-Dinaridic-Pannonian triple junction. Int. J. Earth Sci., 89, 377-389. Schmid, S.M., Bernoulli, D., Fügenschuh, B., Matenco, L., Schefer, S., Schuster, R., Tischler, M. and Ustaszewski, K. (2008) The Alpine- Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units. Swiss J. Geosci. 101, 139-183.

Cretaceous; Sandstones; Heavy Minerals; Geochemistry; Fission Track Thermochronology; Dinarides; Croatia

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