Neogene andesite intrusions along the Carpathian calc-alkaline volcanic arc

Numerous magmatic intrusions follow the Inner-Carpathian calc-alkaline volcanic arc with decreasing age towards the East-Southeast. At the West Carpathians intrusions located: in south-eastern Moravia (internal Biele Karpaty nappe of the Magura flysch unit); and in the Pieniny Mts. between the Magura flysch unit and the Pieniny Klippen Belt. At the internal East Carpathians a big volume subvolcanic body (Ţibleş-Toroiaga-Rodna-Bârgǎu) found between the Gutâi and the Cǎlimani volcanic massifs.
   The Moravian high-K pyroxene-amphibole basalt and andesite intrusions extend southeast of the Morava River. They are sills, dykes and irregular bodies. Emplacement of intrusions was post-tectonic, and the intrusive rocks have been generally affected by postmagmatic alteration. Towards the east at the Slovakian/Polish border, products of intrusive activity form approximately a 20 km long belt of the Pieniny Andesite Line. It post-dates the Early Miocene folding and strike-slip movements. The magma made its way along tensional fissures that opened above a steeply bent downgoing North European Plate. Emplacement of intrusions took place in two phases: 1^st phase intrusions are mostly dykes, parallel with the strike slip fault at the northern part of the Pieniny Klippen Belt; the 2^nd phase intrusions are restricted to the westernmost part of the Pieniny Andesite Line and follow transversal faults that cut the 1^st phase andesites. The Toroiaga intrusive area situated north of the Rodna Mts., consist of a complex subvolcanic intrusions with pierce metamorphic rocks and its southern part, Paleogene to Miocene sedimentary deposits, suggesting a multiphase intrusive activity. Hydrothermal activity and mineralisation processes are related to the 2^nd and 3^rd phase intrusions.
   Major and trace element chemistry of the examined intrusive rocks are indicating subduction-related magmas. Compared to the Pieniny intrusives, the Moravian and the Toroiaga intrusive rocks are relatively enriched in potassium, sodium and other incompatible elements. These latest are lying at the boundary of high-K calc-alkaline- and shoshonitic suites. The LILE enrichment reflects the contribution from the subducted slab, at least the parental magma derived from metasomatised subcontinental lithospheric mantle. Source composition and partial melting was more important then the FC, AFC processes and/or crustal contamination. Partial melting process was triggered by the flux of heat coming from the rising asthenospheric material once the delamination of the subducting European Plate occurred. The B content of the Pieniny andesites is between 2.97 and 29.5 μg/g. The western and the eastern part of the Pieniny Andesite Line can be well separated by the geochemistry. The heat of the 2^nd phase intrusions hydrothermally modified the 1^st phase intrusions, enriched the fluid mobile element content of the rocks. Excluding the enriched B data, the B content in the Pieniny area is not higher, then 10.7 μg/g. The examined Moravian and Toroiaga rocks have higher B content (9.9-20.8 and 6.3-21.5 μg/g respectively). This correlates with the higher K₂O content of these rocks, referring to fluid originating from the crust, while the fluid added to the source of the Pieniny rocks are originating more probably from the subducted sediments. The B data of the Moravian rocks overlap with the B content of West Carpathian andesites (11.1-29.8 μg/g), while the B content of the Toroiaga samples overlap with the Cǎlimani and the Gutâi boron data (4.9-30.2 μg/g). The lower values of the Pieniny area is more in the range measured in back arc, intraplate basalts of the Bakony-Balaton Highland volcanic field (1.6-12.9 μg/g). There is a tight connection between the calc-alkaline volcanism and the intrusive magmatic body formation. In absence of biostratigraphic evidence, a comprehensive K-Ar age study of the intrusive whole rocks was carried out, which was driven to the following origin history: from Moravia until the bend of the Carpathians the magmatism was parallel (~13.5-11 Ma). In the subvolcanic zone of the East Carpathians the intrusion took place between 11.3–7.6 Ma.
   Acknowledgements: This work was supported by the OTKA (K68153).