CHARACTERISTICS OF ROMANIAN LITHOSPHERE FROM DEEP SEISMIC-REFLECTION PROFILING

The tectonic units of Romania contain both Alpine orogenic regions and platforms. The investigations of crustal structure by near-vertical reflection seismic profiling are based on less than 100 lines Unequally distributed and of limited lengths (5-30 km). The seismic features studied are: the crustal seismic reflectivity and transparency; dipping events and diffractions; and the Moho and subcrustal reflectivity. The major common features are: a reflective sedimentary cover of mostly Neogene layers; a weak signal from the sedimentary-basement boundary; a quasi-transparent upper crust; a mid-crust with short and subhorizontal events; a transparent or layered lower crust; and a Moho that is either poorly visible or evidenced by a zone with reflection bands and some subcrustal reflections. The Moesian platform, together with the adjacent Carpathian foredeep, show a mid-crust with short and subhorizontal events, a crust-mantle transition zone in the west, an unclear or prominent Moho and some subcrustal reflectivity. The northern part of the Carpathian foredeep shows strong seismic layering of the lower crust. The central part of the Transylvanian depression is characterized by short and subhorizontal events at mid-crustal level, a slightly reflective lower crust with diffractions and a weak Moho signal. The southern sector of the Pannonian depression is generally marked by a reflective lower crust. The tectonic significance of these seismic signatures is interpreted as follows: a brittle upper crust; a decoupling mid-crustal zone; a lower crust with brittle to ductile behaviour; a possible extensional or isostatic rebalanced Moho and laminated zones with reduced viscosities at the lower crust and upper mantle levels. A series of crustal models based on the reflection seismic sections are presented for several areas of Romania.