Petrology and geochemistry of Egerian-Eggenburgian and Badenian tholeiite-calc-alkaline volcanics from the South Pannonian Basin (Croatia)

In the South Pannonian Basin, bounded to the south by the North Dinarides, two Tertiary post-orogenic tholeiite-calc-alkaline volcanic associations ar e found: 1) the Egerian-Eggenburgian one, composed largely of andesites wit h subordinate basaltic andesites and dacites, and 2) the Badenian one, comp rising basalts, basaltic andesites, andesites, dacites and alkali feldspar rhyolites. Ages of the volcanism are constrained by concordant geological a nd K-Ar data. The petrology and geochemistry of volcanics of both associati ons are constrained by microprobe analyses, major and trace element analyse s and radiogenic isotope data. Despite their different ages, the volcanics of both associations are characterized by similar variations in concentrati ons of major and trace elements and similar variation intervals. Decreasing contents of MgO (10.5-0.30 %), Cr (487-18 ppm), Ni (476-3 ppm) and some ot her elements relative to SiO2 indicate that these volcanics originated by f ractional crystallization from tholeiitic basalt melts, probably generated by partial melting of enriched upper mantle wedge. During fractional crysta llization the primary magma was affected by crustal contamination as indica ted by increased Sr-87/Sr-86 and decreased Nd-143/Nd-144 ratios. In all the se geochemical aspects, Egerian-Eggenburgian and Badenian volcanics are sim ilar to the slightly older tonalite suite in the adjacent easternmost parts of Periadriatic Line (Mts. Pohorje and Karavanke). All three geochronologi c ally successive magmatic events can be explained by a slab breakoff model related to underplating of Apulia (Africa) below Tisia (Eurasia).