Abstract. The Periadriatic Line (PAL) is a remarkable, several hundred kilometer long fault system of the Alpine orogen. Its dextral character was documented by several authors using diverse criteria, but detailed kinematics and timing of movements had not been investigated along its whole length. Structural and paleomagnetic measurements, mapping, and stratigraphic and sedimentological studies have helped to unravel the MiocenePliocene evolution of the Slovenian segment of the PAL.

New laser ablation-inductive coupled plasma-mass spectrometry U-Pb analyses on oscillatory-zoned zircon imply Early Miocene crystallization (18.64 ± 0.11 Ma) of the Pohorje pluton at the southeastern margin of the Eastern Alps (northern slovenia). Inherited zircon cores indicate two crustal sources: a late Variscan magmatic population (~270-290 Ma), and an early Neoproterozoic one (850-900 Ma) with juvenile Hf isotope composition close to that of depleted mantle. Initial εHf of Miocene zircon points to an additional, more juvenile source component of the Miocene magma, which could be either a juvenile Phanerozoic crust or the Miocene mantle. the new U-Pb isotope age of the Pohorje pluton seriously questions its attribution to the Oligocene age 'Periadriatic' intrusions. the new data imply a temporal coincidence with 19-15 Ma magmatism in the Pannonian basin system, more specifically in the styrian basin. K-Ar mineral-and whole rock ages from the pluton itself and cogenetic shallow intrusive dacitic rocks (~18-16 Ma), as well as zircon fission track data (17.7-15.6 Ma), gave late Early to early Middle Miocene ages, indicating rapid cooling of the pluton within about 3 Million years. Medium-grade Austroalpine metamorphics north and south of the pluton were reheated and subsequently cooled together. Outcrop-and micro scale structures record deformation of the Pohorje pluton and few related mafic and dacitic dykes under greenschist facies conditions. Part of the solidstate fabrics indicate E-W oriented stretching and vertical thinning, while steeply dipping foliation and NW-sE trending lineation are also present. the E-W oriented lineation is parallel to the direction of subsequent brittle extension, which resulted in normal faulting and tilting of the earlier ductile fabric at around the Early / Middle Miocene boundary; normal faulting was combined with strike-slip faulting. renewed N-s compression may be related to late Miocene to Quaternary dextral faulting in the area. the documented syn-cooling extensional structures and part of the strike-slip faults can be interpreted as being related to lateral extrusion of the Eastern Alps and/or to back-arc rifting in the Pannonian basin.

[1] Isotopic compositions of marine sediments and fossils have been investigated from northern basins of the Mediterranean to help constrain local oceanographic and climatic changes adjacent to the uplifting Alps. Stable C and O isotope compositions of benthic and planktonic foraminifera from the Umbria-Marche region (UMC) have an offset characteristic for their habitats and the changes in composition mimic global changes, suggesting that the regional conditions of climate and the carbon cycle were controlled by global changes. The radiogenic isotope composition of these fossil assemblages allows recognition of three distinct periods. In the first period, from 25 to 19 Ma, high e Nd values and low 87 Sr/ 86 Sr of sediments and fossils support intense tectonism and volcanism, related to the opening of the western Mediterranean. In the second period, from 19 to 13 Ma the 87 Sr/ 86 Sr ratio of Mediterranean (UMC) deviate from the global ocean, which is compatible with rapid uplift of the hinterland and intense influx of Sr from Mesozoic carbonates of the western Apennines. This local control on the seawater was driven by a humid and warm climate and indicates restricted exchange of water with the global ocean. Generally, the e Nd values of the fossils are very similar to those of Indian Ocean water, with brief periods of a decrease in the e Nd values coinciding with volcanic events and maybe sea level variation at 15.2 Ma. In the third period, from 13 to 10 Ma the fossils have 87 Sr/ 86 Sr similar to those of Miocene seawater while their e Nd values change considerably with time. This indicates fluctuating influence of the Atlantic versus the Paratethys and/or locally evolved seawater in the Mediterranean driven by global sea level changes. Other investigated localities near the Alps and from the ODP 900 site are compatible with this oceanographic interpretation. However, in the late early Miocene, enhanced local control, reflecting erosion of old crustal silicate rocks near the Alps, results in higher 87 Sr/ 86 Sr.Citation: Kocsis, L., T.

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