hrvatski

Traces of the Late Cretaceous to Paleogene Collision in the Dinarides: Evidence from Sandstone Petrography and Geochemistry

The area linking the Dinarides with the crystalline basement of the Pannonian Basin marks the position of a suture zone between tectonic units derived from Africa and Europe. The final closure of a remnant branch of the Mesozoic Neotethys ocean at the end of the Cretaceous was a precursor to collision and the ensuing main phase of nappe stacking and uplift of the Dinarides in the Paleogene. This important evolutionary phase is recorded within syncollisional basins concentrated along and in the areas adjacent to the Sava zone, a tectonic unit extending along the margin of the present- day northern Dinarides (JELASKA et al., 1969 ; PAMIĆ et al., 2002). This study of Upper Cretaceous to Paleogene sedimentary rocks exposed in the western segment of the Sava zone and neighboring areas (Zrinska gora Mt., Medvednica Mt., Žumberak Mts., Cetingrad area) aims at constraining the character of the source areas exposed and eroded in the evolving collision zone. Following a period of tectonic quiescence and widespread deposition of pelagic limestones in the Campanian (BABIĆ & ZUPANIČ, 1976), a relatively rapid increase in siliciclastic influx heralded the advancement of thrusting and flexural foreland formation along the margin of the Adria plate. Arenites within the Campanian to Eocene deposits record multiple ‘crystalline’ and ‘carbonate’ sources. Maastrichtian and some of the Paleocene sandstones are dominantly composed of quartz and sedimentary and very low- to low-grade metamorphic lithics, along with mafic lithics. Heavy mineral fraction of these sandstones is typically composed of apatite, zircon, tourmaline, rutile and variable amounts of Cr- spinel. Together with geochemical data, this indicates a mixed felsic-ophiolitic provenance, probably reflecting erosion of thrusted units of the Adria plate. In the Paleocene and Eocene there was an introduction of felsic and mafic volcanic lithoclasts and plutonic/hypabyssal rock fragments, as well as higher-grade metamorphics. Heavy mineral fractions became strongly dominated by epidote group and garnet, while geochemical data indicate a strong felsic signature and a negligible ophiolite contribution. This sediment was likely derived from the erosion of the magmatic arc that formed along the subduction zone of the Adria plate underneath Europe, as well as from metamorphic units exhumed in the accretionary wedge and/or possibly from the Tisza unit of the overriding plate. Calcarenites interbedded with sandstones and marls are composed entirely of bioclasts, including large benthic foraminifera (Lepidorbitoidinae and Clypeorbinae) and fragments of echinoderms (echinoids and crinoids), corallinaceans (mostly Subfamily Melobesioideae) and bryozoans (mostly fragments of erect rigid colonies). These deposits indicate sourcing from shallow marine carbonate environments that are present in the stratigraphic record of the Sava zone and neighboring areas and represent phases of marine transgression along emerging tectonic units uplifted within the collision zone. Support by the Croatian Science Foundation (IP- 2014-09-9541) is acknowledged.

Provenance, Cretaceous, Paleogene, Internal Dinarides, Sava zone

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