Complex metamorphic zonation of the Thaya dome: result of buckling and gravitational collapse of an imbricated nappe sequence

Abstract

AbstractThe metamorphic isograd geometry and dome structure of the Thaya tectonic window, which emerges through the Moldanubian nappe pile at the eastern margin of the Bohemian Massif, is interpreted as a result of large-scale buckling of an imbricated nappe sequence. This large-scale mechanical instability was initiated by the blocking of passively transported hot viscous rocks to shallow crustal levels. The wavelength and shape of the buckle fold is controlled by the greatest thickness of the uppermost nappe and by the low ratio of strong orthogneiss to weak micaschists in individual nappes. The steep inclinations of the thrust surfaces and the oblique movement of the crustal multilayer minimizes the role of gravity on fold generation. Medium-scale gravitational folds originated at the end of the buckling of the nappes and are associated with the late sliding of the nappes away from the core of the anticline during late exhumation. Thermal, rheological and fold calculations are presented which document and explain the mechanism of folding of large-scale crystalline nappes.