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 r eflection seismic profiling are based on less than 100 lines Unequally distributed and of limited lengths (5-30 km). The seismic features st udied 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 N eogene layers; a weak signal from the sedimentary-basement boundary; a quasi-transparent upper crust; a mid-crust with short and subhorizont al events; a transparent or layered lower crust; and a Moho that is ei ther poorly visible or evidenced by a zone with reflection bands and s ome subcrustal reflections. The Moesian platform, together with the ad jacent Carpathian foredeep, show a mid-crust with short and subhorizon tal 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 cru st. The central part of the Transylvanian depression is characterized by short and subhorizontal events at mid-crustal level, a slightly ref lective lower crust with diffractions and a weak Moho signal. The sout hern sector of the Pannonian depression is generally marked by a refle ctive lower crust. The tectonic significance of these seismic signatur es is interpreted as follows: a brittle upper crust; a decoupling mid- crustal zone; a lower crust with brittle to ductile behaviour; a possi ble extensional or isostatic rebalanced Moho and laminated zones with reduced viscosities at the lower crust and upper mantle levels. A seri es of crustal models based on the reflection seismic sections are pres ented for several areas of Romania.