Neogene exhumation of the Variscan Szeghalom Dome, Pannonian Basin, E. Hungary

Abstract

The Pannonian Basin consists of several deep sub-basins separated by uplifted basement highs. One of the largest and deepest sub-basins is the Be Âke Âs Basin in SE Hungary which is surrounded to the north by several crystalline domes. Of these, the Szeghalom Dome is the best known petrologically, and has been used for studying the Neogene exhumation history of the area.On the basis of metabasite bulk chemistry, the Szeghalom Dome can be subdivided into four distinct zones, the borders of which correspond closely to geophysical anomalies. The four zones exhibit different pre-Variscan and Variscan pressure±temperature± time (P±T±t) histories. In zone I, high-pressure relics (600 C, >12 kbar) occur. Peak-metamorphic conditions of the main Barrovian overprint were c. 700 C and 6 kbar, and amphibole K/Ar ages scatter around 260 Ma. Zone II shows similar characteristics, with the formation of anatectic granite at peak conditions. K/Ar ages are as low as 220 Ma. Zones III and IV show similar evolution to each other with high-grade Barrovian relics (700 C), peak metamorphism at 570 C and amphibole ages of 300 Ma.Throughout the dome, ®ngerprints of a three-fold Neogene tectonic evolution can be observed. An early detachment fault formed quartz±feldspar±mylonite in zone IV, while chloritic breccia developed at the border of zones II and III. Following the thermal subsidence phase of the basin evolution, the area was dominated geodynamically by the reactivation of older strike-slip fault systems. These movements were responsible for the horizontal transport of the crystalline blocks at both the southern and northern¯anks of the dome.

Localisation of ductile and brittle shear zones along the Szentlőrinc-1 well in the Mecsekalja Zone using quartz microstructural and well-log data

“…Comparable structures have since been found in numerous places such as the Cordillera of Western North America (Kerrich 1988;Lister and Davis 1989;Foster and Raza 2002), the Whipple Mountains, southeastern California (Davis 1988;Lister and Davis 1989;Stockli et al 2006) and the Buckskin Mountains, western Arizona (Davis et al 1979;Heidrick and Wilkins 1980;Brady 2002). Detachment faults and metamorphic core complexes are also well-known structures in the metamorphic basement of the Pannonian Basin, even close to the studied well (Tari et al 1992;Posgay et al 1996;Tari et al 1999;M Tóth et al 2000;Schubert and M Tóth 2001;Zachar and M Tóth 2004).…”

“…The Variscan tectonic events were followed by a pervasive extension in the Jurassic (Csontos et al 1992;Haas and Péró 2004) and then the nappe formation in the Cretaceous (Tari et al 1999;Haas and Péró 2004). As a result of the complex basin subsidence in the Neogene (Bergerat 1989;Tari et al 1992;Horváth and Cloetingh 1996;Csontos and Nagymarosy 1998), more kilometre deep sub-basins (Békés Basin, Makó Trough) and metamorphic basement highs (Tari et al 1992(Tari et al , 1999M Tóth 2004, Schubert andM Tóth 2001;M Tóth et al 2000;M Tóth and Zachar 2006) covered with several km thick sediment were formed. The basement formations deformed intensively during the Neogene subsidence.…”

“…The basement formations deformed intensively during the Neogene subsidence. As a result of the complex tectonic evolution, the crystalline basement is made up from blocks with various metamorphic and structural evolutions (M Tóth et al 2000;Schubert and M Tóth 2001).…”

“…Petrological interpretation of the core material at numerous localities confirms the presence of low-angle faults, which separate blocks of different metamorphic evolutions inside the basement. In the Szeghalom Dome crystalline block, M Tóth et al (2000) described different zones with significantly distinct metamorphic and structural evolution. By detailed microstructural evaluation of a single borehole, the adjacent rock types with different P-T histories are separated by well-developed breccia zones of several tens of metres width (Molnár et al 2014b).…”

Evolution of the arc-derived orthogneiss recorded in exotic xenoliths of the Körös Complex (Tisza Megaunit, SE Hungary)

“…Previous studies (Balázs et al 1986;Szederkényi et al 1991) suggested that the main lithologies are identical as in all neighbouring highs. Based on these results, the basement in the study area can be divided into three realms separated by postmetamorphic tectonic zones (Tóth et al 2000).…”