Geochemical evolution of Oligocene and Miocene magmatism across the Easternmost Periadriatic Lineament

Abstract

The easternmost end of the Periadriatic Lineament (PAL) is situated at the complex Alps-Dinarides-Pannonian Basin triple junction in Slovenia and Croatia. Tonalitic plutonism ceased along the PAL as a whole at the end of Oligocene time but not at its easternmost segment, where it continued as volcanism on both sides of the PAL in Early-Middle Miocene times. The paper deals with geochemical modeling of PAL magmatism, in order to put forward a viable petrogenetic model to explain the continuation, compatible with recent geotectonic interpretations in the area. Geochemical modeling of major and trace elements recognizes two groups of volcanic rocks, the Northern and the Southern one, geographically separated by the PAL. Geochemical trends broadly resemble those of the back-arc-trench- arc duality. The magma source was chemically enriched lithospheric mantle, metasomatized during an earlier subduction- related episode. The Northern group was formed by lower degree melting of garnet peridotite, whereas primary magmas of the Southern group were formed by extensive melting of garnet and/or spinel peridotite, developing a tholeiitic-calc- alkaline character. In Miocene times, melting of the mechanical enriched lithospheric mantle was driven by still unobstructed rise of the hot, convective astenosphere, after detachment of the subducted slab and steady lithospheric attenuation and extrusion of ALCAPA. In contrast, in the central portion of the PAL, continuing collision restrained magmatic activity. Different depth of melting arises from different thickness of the lithospheric blocks, south and north of the PAL.