On the Precambrian tectonics of Bulgaria |
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| Authors: | IS Zagor?ev |
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| Institution: | Geological Institute, Sofia Bulgaria |
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| Abstract: | The Precambrian basement of Bulgaria consists of two sharply defined units: the Upper Precambrian—Lower Paleozoic (?) Diabase-phyllitoid (Vlasina) complex, characterized by greenschist facies metamorphism, and the high-grade (amphibolite facies) basement (Thracian massif), subdivided into Rhodopian and pre-Rhodopian complexes. According to the style and dominant fold trend five Precambrian structural zones are defined within the Thracian massif: Ograzhden Anticlinorium; Sredna Gora Anticlinorium; Rhodope Anticlinorium; Pirin structural zone; Upper Thracian structural zone.The pre-Rhodopian development (4 major fold phases in amphibolite facie metamorphic conditions) resulted in formation of a grate-shape structure with centrifugal vergence, and smooth curvature of the dominant trend. The consecutively formed Rhodopian complex was folded following a simple “dome-and-basin” interference pattern, in amphibolite facies conditions, and uplift tendencies for the peripheral anticlinoria. The structure was complicated by torsion in the Pirin zone, and by setting up of the first (“ancestral”) fault zones along the junction lines between the separate Precambrian structural zones. After erosion the Diabase-phyllitoid complex covered the periphery of the Thracian massif and incorporated fragments of it as cores of positive structures. The Precambrian structural plan has been largely inherited by later (Hercynian and Alpine) tectonics. |
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