Tha Vitoša central magmatic structure

Vitoša central magmatic structure comprises many consecutively formed magmatic bodies referred to two series: Ca-alkaline and K-alkaline. Each series is further subdivided into four complexes: volcanic, subvolcanic, intrusive and postintrusive. The volcanic complexes of the two series are divided by regional unconformity which marks a considerable time break in the volcanic activity. The other complexes show cross-cutting relationships. The Vitoša paleovolcanoe is the initial element of the structure. It is of Ca-alkaline composition, shows confocal structure with polygonal (ring) and radial faults and dykes. Apart from the Ca-alkaline volcanic and subvolcanic rocks the volcanoe is marked also by Ca-alkaline intrusive and postintrusive rocks which crop out in its vent parts or form small intrusive bodies along radial faults. They are interpreted as offshoots of Plana pluton but emplaced at higher stratigraphic level. Elements of the structure are also the K-alkaline intrusive and postintrusive complexes which intrude the central parts of the volcanoe. However, they are only structurally related to the volcanoe. In the present-day structural plan, the Vitoša central magmatic structure is a circular morphostructure (dome), complicated by numerous activated fault segments of the regional and local fault network which define a complex internal block pattern. The development of the structure began in the Early Senonian. Two tectonomagmatic stages and a neotectonic stage are distinguished. During the early (Coniacian-Santonian) tectonomagmatic stage, magma complexes of Ca-alkaline composition formed in close structural and genetic relationships to the Vitoša stratovolcanoe. During the later (Campanian) tectonomagmatic stage originated K-alkaline magmatic rocks related to another volcanoe located to the northwest. The tectonomagmatic stages took place in the conditions of impermanent rifting. The first two phase of each stage (volcanic and subvolcanic) characterize the opening of the rift, marked by numerous telescoped dykes. The third (intrusive) phase was preceded by compression witnessed by several thrust and strike-slip fault. The final shaping of the structure as a positive circular morphostructure (dome) occurred during the neotectonic stage.