Beihefte zur European Journal of Mineralogy, vol. 11, 1999 No. 2, S. 1—6, Stuttgart, 1999 DMG-Tagung 1999 Exkursion A Synoptic geology of Hungary Miklós KÁZMÉR Department of Palaeontology, Eötvös University, Budapest, Ludovika tér 2, H-1083 Hungary; e-mail: [email protected] Introduction The geology of Hungary is best described as an orogenic collage, assembled in the Miocene, and subsequently covered by sediments. Inselbergs serve as outcrops, displaying what is below the Miocene to Quaternary cover. Since the ratio of geologists per km2 of hard rock is possibly the highest in Europe next to The Low Countries, regional geology is quite well known (Trunkó, 1996). Correlation between outcrops is best served by thousands of deep boreholes and an extensive network of seismic profiles (results of sixty years of hydrocarbon exploration), making the Pannonian Basin one of the best known great basins of the world. Hungary is enclosed by the Alps, the Carpathians and the Dinarides. Orographic pattern is that of a continuous, mildly arcuate southern mountain chain extending from the Southern Alps to the Dinarides, and a northern, highly curved loop ranging from the Eastern Alps through the Carpathians to the Dinarides. The Fig. 0.1. Schematic tectonic map of the Pannonian Basin and the surrounding mountain edifice (Bada, 1999). 1: molasse belt; 2: flysch belt; 3: pre-Tertiary units; 4: Neogene volcanics; 5: Pieniny Klippen Belt; 6: strike-slip fault; 7: normal fault; 8: thrust fault. Ba: Balaton Line, D: Drava Line; FS: Fella−Sava Line, L: Lavanttal Line; Me: Medvednica fault; MMZ: Mur–Mürz–Žilina Lineament; PAL: Periadriatic Lineament; S: Sava Line. 2 Fig. 0.2. Miocene emplacement of Alcapa and Tisza blocks of the Carpathian-Pannonian system (Bada, 1999). a: Late Ottnangian (18 Ma), b: Karpatian (17−16 Ma), c: Middle Miocene (14−11 Ma), d: Late Miocene (11−9 Ma). BM: Bohemian Massif: MHZ: Mid-Hungarian fault Zone, MP: Moesian platform, NPU: North Pannonian Unit (Alcapa), PAL: Periadriatic Lineament. latter has major importance for us, since its tectonic units outcrop as inselbergs within the Pannonian Basin (Bada et al., 1998; Bada, 1999; Fig. 0.1). Nappes of this mountain frame around the Pannonian Basin formed in different times during the Jurassic and Cretaceous in both major terranes: the Alcapa (abbreviated from Alpine-Carpathian-Pannonian) in the NW and the Tisza Terrane in the SE. Both are highly composite terranes, emplaced in their present-day position during Miocene tectonic escape and rotation (Fig. 0.2, Bada, 1999; Fodor et al., in press). They are separated by the subsurface Mid-Hungarian Line, essentially a complex Miocene tectonic zone of major strike-slip displacement (Csontos & Nagymarosy, 1998). A set of intermontane basins, collectively called the Pannonian Basin occupies the space within the Carpathian loop. These were formed during and after the emplacement of the Alcapa and Tisza terranes (Csontos, 1995). Tectonic units Mesozoic palaeobiogeography of inselbergs within the Pannonian Basin shows major contrasts: northern ones (Transdanubian Central Range) display southern, Tethyan affinities, while the southern ones (Mecsek, Villány) display northern, European affinities, especially in the Jurassic. This observation of Géczy (1973, 1984) based on Jurassic ammonites at the advent of plate tectonics was later corroborated by several authors (e.g. Vörös, 1993, on Jurassic brachiopods, Bujtor, 1993, on Cretaceous ammonites). This means that the basement of the Pannonian Basin is not uniform, but is composed of at least two major blocks. Palaeomagnetic studies of the inselbergs yielded similar results. Two domains of opposite rotations were outlined: while the Transdanubian Central Range, Bükk Mts. and Inner Western Carpathians display Tertiary counter-clockwise rotation (for latest results see Márton et al., 1996), the Mecsek, Villány and Apuseni Mts. inselbergs together with the Eastern and Southern Carpathians show Tertiary clockwise rotation (e.g. Márton, 1987; Pãtrascu et al., 1994). These data delineate two major, more or less rigid continental microplates (Balla, 1984; Csontos et al., 1992) with different Mesozoic history, emplaced during the Tertiary. Their common boundary is the subsurface Mid-Hungarian Line (Csontos & Nagymarosy, 1998). 3 The Alcapa Block is located north of the Mid-Hungarian Line. Its northern boundary is the Pieniny Klippen Belt, a zone of Cretaceous nappes which suffered left-lateral shearing in the Miocene (Birkenmajer, 1986). The two major, Tertiary subunits are the Western Carpathians in the north, its nappes being correlated to those of the Eastern Alps (Fuchs, 1984), and a southern unit composed of the Transdanubian Central Range and the Bükk Mts. This is compared best to the Southern Alps (Kázmér & Kovács, 1985). The two subunits display counter-clockwise rotation but of different magnitude (Márton et al., 1992). The Tisza-Dacia Block is located south of the Mid- Hungarian Line, and extends as far as the Sava Line in the south, and includes the Eastern and Southern Carpathians (Csontos, 1995). It suffered uniform clockwise rotation in the late Tertiary. Two minor (Mecsek and Villány) and one major (Apuseni Mts.) inselbergs concern us within and next to Hungary. The Alcapa and Tisza–Dacia blocks were emplaced during the Miocene. The northward push of the Adriatic Block initiated the extrusion of wedge-shaped tectonic lamellae in the Alps (Frisch et al., 1998). A consequence of this tectonic reorganisation was the eastward displacement and rotation of both the Alcapa and Tisza– Dacia blocks (Csontos, 1995). The subduction of oceanic crust external to the Carpathians produced a calc-alkaline volcanic arc ranging from the Visegrád Mts. in the west in Hungary (Day 1) to the Harghita Mts. in the east in Romania (Pécskay et al., 1995). Behind the arc the extensional Pannonian Basin developed, characterised by thin crust, elevated mantle and consequent high heat flow (Horváth, 1993). Scattered alkaline (Szabó et al., 1992) and potassic (Harangi et al., 1995) volcanism is associated with the young phases of extension. Today the Carpathian-Pannonian system is under compres- sion stress between the northward-moving Adriatic Microplate and the European Plate (Bada, 1999). Although we are witnesses to the last moments of an active subduction in the Vrancea Zone at the SE corner of the Carpathians in Romania (remember the earthquake which destroyed Bucharest in 1977), the cessation of Fig. 0.3. Stratigraphic column of the Mecsek all volcanic activity both in the Pannonian Basin and in the Zone after Kázmér (1986). 1: Crystalline base- Carpathians testifies that major tectonic displacements are dis- ment, 2: Upper Carboniferous clastics, 3: continued. However, stress-induced crustal-scale uplift and sub- Coarse, polymictic clastics, 4: rhyolite, 5: sidence characterises several parts of the region, elevating moun- Conglomerate, 6: Red siltstone, 7: Sandstone, 8: Conglomerate and sandstone, 9: Werfen tains and lowering alluvial basins (Horváth & Cloetingh, 1996). beds, 10: Muschelkalk, 11: Black limestone and marl, 12: Sandstone: Keuper, 13: Coal The Mecsek Zone (Day 2) measures, 14: Rhyolitic tuffite, 15: The Tisza Unit is exposed in two inselbergs, Mecsek (Fig. 0.3) and Fleckenmergel, 16: Crinoid limestones, 17: Villány in Hungary. These are outcrops of the westward extension Red nodular limestone and marl, ammonitico of Cretaceous nappes of the Apuseni Mts. in Romania. Their rosso, 18: Cherty limestone 19: Nodular lime- stone; 20: Nodular, fossiliferous limestone, correlation is known through numerous boreholes in the Great red, 21: White cherty limestone, 22: Grey, Hungarian Plain (Bérczi-Makk, 1986). marly limestone, 23: Marl, 24: Alkali basalt The Mecsek Mts. gave the name for the northernmost tectonic and various dykes, 25: Marl with zone − nappe − of the Tisza Unit. Its Variscan basement constitutes olisthostromes, 26: Pelagic limestone, 27: a variety of nappes as indicated by the occurrence of metamorphic Pelagic marls with olistostromes, 28: rocks of different grade (Trunkó, 1996:214-215). A thick, Phonolite intrusions, 29: Conglomerate and breccia, 30: Red marl, 31: Flysch, 4 Fig. 0.4. Stratigraphic column of the Transdanubian Central Range after Kázmér (1986). 33: Ammonitico rosso, 34: Hierlatz limestone, 35: Manganese ore, 36: Radiolarite, 37: Ammonitico rosso, 39: Flysch, 40: Cephalopod-tintinnid limestone, 41: Biancone, 42: Crinoid-cephalopod limestone, 43: Siliceous marl, 44: Grey crinoid limestone, 45: Alsópere Bauxite Formation, 46: Munieria marl, 47: Lower pachyodont limestone, 48: Grey siltstone, 49: Upper pachyodont limestone, 50: Glauconite marl, 51: Lamprophyre dykes, 52: Bauxite, 53: Terrestrial clastics, 54: Coal measures, 55: Gryphaea marl, 56: Inoceramus marl, 57: Hippurites limestone, 58: Bauxite, 59: Dolomite fanglomerate, 60: Conglomerate, clay and limestone, 61: Nummulites limestone, 62: Coal measures, 63: Fossiliferous marl, 64: Andesite, 65: Nummulites limestone, 66: Buda marl, 67: Laminated clay, 68: Siliceous sandstone, 69: Foraminifer clay, 70: Fluviatile beds, 71: Marine sands, 72: Marine pelites, 73: Tonalite. The Úrkút manganese deposit is No. 35, bauxite-bearing, karstic unconformities are Nos. 45 (Albian), 52 (Senonian), and 58 (Eocene). uraniferous Late Palaeozoic clastic sequence is overlain by the characteristic sediments of the German-type Triassic: Buntsandstein (variegated sandstone), Muschelkalk (shallow-water limestone), and Keuper (lacustrine