engleski

Tertiary shoshonite volcanic associations from the adjacent areas of the South Pannonian Basin and Dinarides

In the South Pannonian Basin, adjacent to the North Dinarides, rocks of Tertiary post-orogenic shoshonite associations are known at Mts. Krndija (KM) and Fruška Gora (FG) and in the Borač area (BO). They are predominantly trachyandesites with subordinate basaltic trachyandesites. Ages of the volcanic suites are constrained by concordant geological and radiometric K-Ar dates. The ages of the FG volcanic occurrences are Early Oligocene (~35 Ma), the BO volcanic rocks are Egerian-Eggenburgian (~22 Ma) and the KM group is Karpatian (~17 Ma). The petrology and geochemistry of volcanic associations are constrained by microprobe analyses, major and trace element analyses and Sr, Nd and Pb isotopic compositions. Despite differences in ages, the volcanic associations do not show any significant geochemical differences. They are characterized by similar variations in concentrations of major and trace elements. Decreasing contents of MgO, Cr, Ni and some other elements relative to SiO2 indicate that volcanic rocks originated by fractional crystallization from shoshonitic melts, probably generated by partial melting of the metasomatized pargasite lherzolite of upper mantle wedge. During fractional crystallization the primary magma was affected by slight and, to a lesser extent, by moderate crustal contamination, as indicated by Sr and Nd isotope compositions. In all these geochemical aspects these volcanic suites can be mutually correlated and successive magmatism can be genetically related to the evolution of the Dinarides and explained by a slab-breakoff model related to underplating of Apulia (Africa) below Tisia (Euroasia).

Tertiary; shoshonite; Pannonian basin; Dinarides

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