Paleogene geology and exhumation history of the Dinarides as reflected by provenance signatures of synorogenic siliciclastic sediments
Zusammenfassung der Projektergebnisse
In this project a sedimentary provenance study was undertaken in Cretaceous to Tertiary basins of the Dinaride orogen. The major objective was to put new constraints on the orogenic evolution of this integral, yet one of the least known segments of the European Alpine chain. We have taken on the approach of in-depth characterizing the detritus derived from major tectonostratigraphic units, focusing on information extracted via geochemistry, geochronology and fission-track thermochronology of single detrital grains. We used these results to describe the paleogeology and understand sediment dispersal patterns, which are all dependent on the large-scale crustal and surface processes involved in the Alpine orogeny. The Cretaceous Bosnian Flysch and equivalent formations were shown to have been deposited in front of a complex continental and ophiolitic nappe system, its material mostly derived from the upper plate. The detrital material retains zircon and monazite geochronological evidence for the erosion of continental basement and peculiar, probably subduction-related, intra-oceanic granitoids. Deposition of the clastic wedge was controlled by rapid exhumation of the continental basement units, as indicated by synsedimentary zircon FT cooling ages in the Early Cretaceous. In the outermost zones of the Dinarides, a series of wedge-top basins developed in the Tertiary. Calcareous nannofossil analysis suggests a foreland-directed younging of the sedimentation (up to the Neogene in accessible onshore outcrops with the actual orogenic front being situated further W offshore the Adriatic coast) and thus provides an important link between Cretaceous thrusting in the innermost part of the imbricate wedge, and present-day deformation at the orogenic front. Nearly all fossil assemblages comprise reworked nannofloral elements, many of them having non-overlapping species ranges. This implies extensive sediment reworking throughout the Cenozoic, and probably serves as a robust explanation for the observed large-scale similarity in heavy mineral assemblages as well as in the geochemistry of garnet and in zircon fission track ages. Careful coupling of U/Pb dating to fission track analysis of zircon on a single-grain level demonstrates that Outer Dinaride sediment evolution in the Cenozoic must have involved a major step of sediment input from the Austroalpine, Tisza or Pelagonian Units following the Late Cretaceous exhumation and cooling of these tectonic units.
