International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

K-Ar geochronology and petrography of the Miocene Pohorje Mountains batholith (Slovenia)

Pages: 247 - 260

Authors: MIRKA TRAJANOVA, ZOLTAN PECSKAY, TETSUMARU ITAYA

Abstract: A series of K-Ar ages from the Alpine Pohorje Mountains igneous complex is presented. The granodiorite with dacite was emplaced in a dynamic environment in the form of a single major intrusion, between 19–18 Ma (Ottnangian), into still hot metamorphic host rocks. The granodiorite includes an older mafic portion of transitional diorite to pyroxenite composition, cezlakite, yielding an age of ~20 Ma. Granodiorite magmatism was followed by major tectonic activity causing uplift of the Pohorje Mountains complex, and the whole batholith cooled rapidly at rather shallow depths, yielding uniform cooling ages of around 16.7 Ma, at the Karpatian/Badenian boundary. The process was accompanied by the intrusion of minor rhyodacitic dykes in the north-western part of the Pohorje Mountains complex and of thin lamprophyre dykes mostly into the metamorphic rocks on the western margin of the pluton. The pyroclastics within the Miocene sedimentary rocks attest to the latter’s young age and subaerial emplacement conditions. In the final stage of the magmatism, aplite-pegmatite melts intruded into the solidified granodiorite. The Pohorje Mountains batholith represents the westernmost intrusion along the extensional structures of the Pannonian Basin. The main magmatic activity could be related to deep transtensional fractures of the Labot fault system north of the Periadriatic zone. The tonalite and granodiorite from the Pohorje Mountains are petrologically different and younger than the Oligocene tonalite from Zelezna Kapla (Eisenkappel), as well as the tonalites further west, and the tonalites buried in the Zala Basin in Hungary (roughly between 40 to 30 Ma), which belong to Paleogene Periadriatic intrusions.

Keywords: Miocene, Pannonian Basin, Periadriatic zone, Pohorje, Labot fault, K-Ar dating, granodiorite batholith

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