A Gyűrűfűi Riolit Formáció kőzettani vizsgálatának eredményei a Villányi-hegység északi előterében

Abstract

In this study rocks samples of Gyűrűfű Rhyolite Formation were observed from deep drillings at northern foreland of the Villány Mts. Remained cores and thin sections from Bisse-1, Peterd-1, Szava-1, Vókány-2, Egerág-7 and Szalánta-3 drillings were available in varying -but generally restricted -number for the petrographic reambulation. Based on the new petrographic descriptions and the previous reports, 2 main lithological groups were distinguished in the area: lava rocks and pyroclastites. Based on the mineralogical composition and texture the following rock types are distinguishable:(1) pyroclastites with rhyolitic composition (Peterd-1; Vókány-2, upper section; Egerág-7, upper section; Szalánta-3, upper section and presumably Bisse-1, upper section); (2) lava rocks with rhyolitic composition (Bisse-1, lower section; Szava-1; Vókány-2, lower section); (3) lava rocks with dacitic composition (Egerág-7, lower section); (4) lava rocks with rhyodacitic-dacitic composition (Szalánta-3, lower section).At northern foreland of the Villány Mts, the magmatic activity started with lava flows (creating a rhyolitic lava dome/lava flow in the area of Szava and Bisse-Vókány and rhyodacitic-dacitic lava rocks in the area of Egerág-Szalánta) and was followed by explosive eruptions, covering the area with thick ignimbrite sheets.Pyroclastites explored by drillings have rhyolitic composition at present but their crystal-rich character may refer to dacitic initial melt composition; resembling to the so-called crystal-rich monotoneous intermediates. These products are connected to reactivated crystal mush from middle-upper crustal magma reservoirs. Considering that pyroclastites were affected by a posterior K-metasomatic process (e.g. adularization of feldspars in rocks of Peterd-1), the modification of their chemical composition cannot be excluded. Further studies of the garnet crystals observed in the pyroclastites of Egerág-7 and Szalánta-3 deep drillings could help to refine the nature of Permian volcanism in the area.Our new results suggest that at northern foreland of the Villány Mts -similarly to analogous regions of European Variscides (e.g. Intra-Sudetic Basin, Southern Permian Basin, Muntii Apuseni) -a chemically complex, possibly long lasting volcanic system worked and produced the rock materials that were formerly handled as one separate stratigraphical marker formation. For further investigation of this system, radiometric age dating of each borehole (U-Pb, zircon) and whole rock (major and trace elements) geochemical analyses are planned.Keywords: Villány Mountains, Gyűrűfű Rhyolite, Permian, pyroclastite, lava rock, garnet, K-metasomatism ÖsszefoglalásMunkánkban a Gyűrűfűi Riolit Formáció Villányi-hegység északi előterében mélyfúrások által feltárt kőzeteit vizsgáltuk. A Bisse-1, a Peterd-1, a Szava-1, a Vókány-2, az Egerág-7 és a Szalánta-3 fúrásokból változó, de alapvetően korlátozott mennyiségű fúrómag és vékonycsiszolat állt rendelkezésre a kőzettani reambulációhoz. Petrográfiai megfigyeléseink, valamint...

Permian felsic volcanic rocks in the Pannonian Basin (Hungary): new petrographic, geochemical, and geochronological results

“…Both K-metasomatism (adularization) and albitization were suggested in the previous reports of uranium ore exploration (Fazekas 1978;Barabásné Stuhl 1988; based on petrographic and geochemical observations). This was confirmed by recent studies based on the petrography of samples of Southern Transdanubia and by XRD analyses of separated feldspar crystals that showed the existence of adularia (Szemerédi et al , 2017. K-metasomatism or albitization are general features of the other Permian felsic volcanic rocks in the European Variscides (Awdankiewicz 1999;Paulick and Breitkreuz 2005;Vozárová et al 2015Vozárová et al , 2016Szemerédi et al , 2017.…”

“…Permian felsic volcanic rocks in Hungary occur in two mega-units of different geological histories that are the Tisza MU and the ALCAPA MU. The Tisza MU is dominantly represented by felsic pyroclastic rocks, while lavas are subordinate and present only within the northern foreland of the Villány Mts (Szemerédi et al , 2017. Felsic volcanic rocks of the ALCAPA MU are represented by lavas and dykes that occur in the Central Transdanubian region and known from boreholes and outcrops.…”

“…b Position of the studied Permian felsic volcanic rock outcrop and the boreholes of Southern Transdanubia, Hungary. Map base is modified after Szemerédi et al (2017). B Battonya, Kel Kelebia, Kk Kékkút, P Polgárdi ◂ The selected 20 outcrop/boreholes of recent study with whole-rock geochemical data are underlined.…”

“…Some samples of the northern foreland of the Villány Mts (boreholes Egerág-7 and Szalánta-3) contain tourmaline and subhedral garnet crystals ( Fig. 2c; Szemerédi et al 2017). The rocks are variably foliated ( Fig.…”

“…Microholocrystalline or felsitic (Fig. 2d), rarely relict perlitic, spherulitic, or granophyric textures of felsic lavas from the northern foreland of the Villány Mts, represents a wide range of rhyolitic lava/dome lithofacies (microcrystalline core, perlitic core, and brecciated variations of them as parts of the outer carapace; Szepesi et al 2016;Szemerédi et al 2017). Two sequences (boreholes Egerág-7 and Szalánta-3) with more plagioclase than potassium feldspar and no porphyric quartz suggest dacitic composition.…”