Architecture of thrust faults with alongstrike variations in fault-plane dip: anatomy of the Lusatian Fault, Bohemian Massif
The Lusatian Fault in the northern Bohemian Massif is one of the most prominent products of the latest Cretaceous to Paleogene thrusting in the Alpine foreland in Europe. Its fault plane dips to the N to NE, typically separating crystalline units in the N from Upper Paleozoic and Cretaceous units in the south. Crystalline units in Lusatia consist of Proterozoic to Lower Paleozoic rocks epi- to mesozonally metamorphosed during the Variscan Orogeny, cut by Cadomian and Variscan granitoid plutons. Anatomy of the fault was studied in outcrops and in a series of test trenches, and the course of fault trace in complex topography was used to determine the dip of the fault. Based on a detailed analysis of brittle structures accompanying the main fault, the Lusatian Fault Belt can be further subdivided into the fault core, zone of wall-rock brecciation, and the damage zone which also includes large-scale dismembered blocks and flanking structures. Other components of the fault belt originated in spatial association with the Lusatian Fault, during its formation (e.g., the drag zone and bedding-plane slips in the footwall-block sediments) or later, during its multi-stage evolution.
A general dependence of fault belt architecture on the orientation of the fault plane to the acting stress can be demonstrated. With the NNE-SSW subhorizontal maximum principal stress calculated for the thrusting episode at the Lusatian Fault, less complex structures appear where the dip of the fault is shallower, and more complex structures including thicker damage zone and drag zone were formed where the fault was steeper. In flat fault segments, competent members of the footwall-block sedimentary package, whose bedding planes were sub-conformable to the fault plane, were sheared during the thrusting and dragged to near-surface levels as dismembered blocks. A progressive eastward increase in the fault dip angle is associated with the appearance of the zone of flanking structures in which the degree of rotation is a function of the fault dip angle. In the eastern part of the fault (fault dip angle of ~60°), the same stress acted at a high angle to the fault plane producing a “bulldozer effect”. Limbs of the flanking structures were overturned, and a parallel, more gently inclined Frýdštejn Fault was initiated as a structure more advantageous for slip movement.
IF (ISI, 2019): 1.279
5 YEAR IF (ISI, 2019): 1.45
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