Integrating Petrography and Geochemistry: New Insights Into Palaeogene Polymict Conglomerates From Zrinska Gora And Požeška Gora Mountains (Sava Zone, Croatia)

Palaeogene syn-collisional basins of the Sava Suture Zone (SSZ) record the sedimentary response to the continental collision between the Adria plate and the Tisza Mega-Unit. This study presents a preliminary investigation of polymict conglomerates from selected localities from Zrinska Gora and Požeška Gora mountains, combining petrography, whole-rock geochemistry and zircon geochronology to constrain sediment provenance and basin evolution.

Petrographic analyses reveal a diverse assemblage of pebble lithotypes, including granitoid, volcanic, and metamorphic clasts, reflecting multiple source rocks. Petrographic characteristics provide initial indications that certain pebble lithologies may correlate with nearby inselberg sources, but these interpretations remain tentative and must be further evaluated through whole-rock geochemistry and constrained by zircon U–Pb geochronology. The presence of granitoids and volcanics indicates a significant contribution from magmatic units of the SSZ, while metamorphic pebbles suggest additional input from the pre-Eocene metamorphic basement.

Preliminary whole-rock geochemical data from selected pebbles indicate A-type granite affinities and alkaline magmatic signatures, consistent with previously documented SSZ magmatism. Ongoing geochronological analyses of zircons separated from representative pebbles aim to provide more robust age constraints on source lithologies. These data will enable direct correlation between sedimentary components and their parental magmatic and metamorphic units, offering critical temporal constraints on sediment supply and tectono-magmatic evolution.

The integration of petrographic, geochemical, and geochronological datasets provides new insights into sediment routing systems and provenance evolution in Palaeogene syn-collisional settings of the western branch of the SSZ. This work contributes to a broader understanding of the interplay between subduction, collision, and basin development within the Alpine-Mediterranean orogenic system. The presented work is supported by the Croatian Science Foundation Project SECret (HRZZ IPS-2023-02-2683).