Structure and Alpine evolution of Bulgaria

The territory of Bulgaria covers parts of two major tectonic units - the northern part of the Alpine thrust belt on the Balkans and its foreland - the Moesian platform.
   These two major tectonic units are generally recognized by all Bulgarian geologists but there has been and still is going on a considerable debate about their further subdivision into higher-ranking units, their structure and geodynamic interpretation.
   Earlier tectonic schemes were based on the geosynclinal theory. According to the classical and most popular concept of Бончев (1971, 1986), the northern branch of the Alpine orogen in Bulgaria developed within the geosynclinal "mobile space" between two cratons – the MIoesian platform and the Thracian "median massif'. From this viewpoint, the territory of Bulgaria was divided into three major tectonic units: Thracian massif (Serbo- Macedonian and Rhodope massifs), Alpine orogen and Moesian Platform. The orogen was further subdivided into "morpho structural zones": Balkanides (with Fore-Balkan and Stara Plan ina zones), Srednogorie, Kraishtides and South Carpathians. The tectonic map of Йовчев et aI. (1967, 1971) is based on a similar, slightly modified approach and portrays four major tectonic units: Rhodope massif, Moesian platform, AIpine fold belt (with seven zones) and Superimposed Tertiary depressions.
   Since the advent of the plate tectonic theory three decades ago, numerous controversial and contradicting tectonic models for the structure and geological evolution of Bulgaria have been proposed (Boyanov et aI., 1989; Dabovski et aI., 1989, Dokov et aI., 1989; Антова et aI., 1996 and many others). They are based on the concept that the Alpine evolution and structure of the Balkan Peninsula were controlled by continuous subduction and multiple collisions along the south facing continental margin of Eurasia. These models differ in the approach to define tectonic units, but share one common point of view - the Alpine thrust belt is a mosaic of proximal and exotic continental fragments that accreted to Eurasia during the closure of Tethys. So far, however, a published modern tectonic map of Bulgaria is not available.
   In order to arrive at the most objective tectonic model of any territory, it is necessary to compile and analyze as complete a range of geological parameters as possible, including lithology, palaeontology, stratigraphy, structure, volcanism, plutonism, metamorphism, radiometric data and geophysics. This approach has been adopted by the authors in an attempt to develop a new model for the Alpine structure and evolution of Bulgaria. The present paper is a summary of the main results.