Tectonic development, morphotectonics and volcanism of the Transdanubian Range: a field guide

摘要

Between 24th August and 1st September, 2002 the Geological Institute of Hungary held an International Workshop on "Application of GPS in plate tectonics, in research on fossil energy resources and in earthquake hazard assessment". Following the plenary sessions a short field trip ran to western Hungary with an aim to present field sites where the interplay of neotectonics, geomorphic evolution, various denudation processes, sedimentary systems and interaction of volcanism and sedimentation in a f luvio-lacustrine environment can be studied. The Balaton Highland represents a classical area where the Middle Triassic asymmetric rifting of the Neo-Tethian carbonate platform was documented. Classical and recent studies described the major elements of the Cretaceous shortening phase. The southeast-vergent thrusts can be connected to the formation of the Transdanubian syncline structure, and probably also to nappe emplacement of the whole unit Miocene and eventually Plio-Quaternar y reactivation of some of the older thrusts could represent a working hypothesis for future neotectonic studies, dealing with the neotectonic uplift of the Balaton Highland and formation of the Lake Balaton depression Some publications and recent mapping work in the Transdanubian Range revealed the deformation of the late Miocene (Pannonian to Pontian) sequences This Pliocene or Quaternary deformation shows varying kinematics, from blind reverse faulting and folding (Zala Hills) to normal faulting (Vertes Hills) through transpressional or transtensional fault zones (Lake Balaton, Vertes Hills), The timing and connection of this deformation pattern to measurements of recent stress field and recent crustal motion (GPS) represents the future challenge of neotectonic research. Western Hungary is also a region, where Neogene small-volume alkali basaltic intracontinental volcanism occurred. The systematic study of the strongly eroded volcanic edifices, often degraded to their volcanic root zones, gives a good opportunity to estimate the level of erosion over a large area. Recent researches demonstrated the presence of extensive Pannonian sedimentary cover in syn-volcanic time. The distribution of volcanic vent remnants, their asymmetric shape and their level of erosion are in good concert with other geological field data supporting a 100 m-scale erosion of Pannonian sedimentary cover and the presence of hydrogeologically active zones such as valley systems, swamps, wetlands in the Pliocene Our recent analyses reinforce earlier assumptions that wind erosion played important role in formation of the Transdanubian valley system Evidences include the occurrence of ventifacts, wind-polished rock surfaces at different topographic positions, the presence of deflated large-scale landforms (yardangs), the lateral transition of wind-blown sand and loess, and the relative scarcity of fluvial sediments. The large shallow lacustrine system and its late Pleistocene-Holocene sediments give opportunity to connect climatic and landscape evolution. Our present results suggest that only a combined tectonic, volcanologic, geochronologic, sedimentologic approach can help to unravel Plio-Quaternar y deformation and related landscape evolution.