LITHOSPHERIC STRUCTURE ACROSS THE CARPATHIANS, VARISCIDES, AND OUACHITA OROGENIC BELT: SOME RECENT RESULTS AND COMPARISONS

Southern North America and Central Europe share many aspects of their Neoproterozoic and Phanerozoic tectonic evolution. The break-up of Rodinia created the continental blocks we call Laurentia and Baltica. Passive margins developed after the rifting, and these margins were deformed by series of Paleozoic orogenies.Thanks to a series of large seismic experiments in Europe and the southern U. S,, we have been conducting comparative analyses of major structures in Laurentia and Baltica. The efforts in Europe primarily targeted the structure and evolution of the complex collage of major tectonic features in the Trans-European suture zone (TESZ) region, as well as, the Carpathian Mountains and the Eastern Alps, the Pannonian basin, and the Bohemian massif. In the TESZ region, these efforts have delineated the rifted margin of Baltica, and it is quite similar to crustal models we have developed for the Ouachita margin. Our integrated seismic and gravity modeling efforts indicate that the Variscan orogeny in Central Europe and the Ouachita orogeny appear to be the result of soft collisions that have left the pre-orogenic rifted margins largely in tact. In Baltica, the amount of intraplate deformation accompanying the Variscan orogeny is modest. However, the Ancestral Rocky Mountains are enigmatic in that the amount of intraplate deformation is very large and correlates with the Ouachita orogeny in time. In the case of the Carpathians, three possible tectonic models are consistent with the observed velocity structure. These models are not mutually exclusive because of the complex Mesozoic and Cenozoic tectonic evolution of the region. The first model invokes “old” (northward) subduction zone of the Pannonian lithosphere under East European craton in the Jurassic - Lower Cretaceous. The second model invokes lithospheric scale collision to form a “crocodile” structure where Carpathian-Pannonian upper crust obducted over the crystalline crust of the EEC and Carpathian-Pannonian mantle lithosphere underthrusted cratonic crust. The third model invokes thinning of the Pannonian lithosphere due to extension, together with “young” (southward) subduction of the EEC lithosphere in the Tertiary (Miocene). It is interesting to note that none of these orogenic events involved magmatic activity that is remotely voluminous as that found in the Andes.