Petrophysical control on the mode of shaering in the sedimentary rocks and granitoid core of the Tatra Mountains during Late Cretaceous nappethrusting and folding, Carpathians, Poland

Abstract

In the Tatra Mts., the variability of structures within the granitoid rocks and their sedimentary complexes depends on the physical properties of the rocks, particularly on their porosity and sensibility to dissolution. In the relatively homogeneous and low porosity granitoid rocks, the shear surfaces are planar and smooth without damage zones around the shear planes. They did not develop open spaces during shearing, which prevented fluid migration and hydrotectonic phenomena. In the sedimentary rocks, mechanical, mostly bedding anisotropy controlled the geometry and morphology of the shear zones. High porosity and recurring changing in pore fluid pressure determined the cyclic character of the thrustrelated shearing processes. Fluids appearing within the thrust-fault fissure played the key role in tectonic transport and selective mass-loss processes (hydrotectonic phenomena). The mass-loss process was an effect of mechanical disintegration, pressure solution and cavitation erosion. The multistage character of the thrusting processes resulted in a gradual increase in mass loss value and in geometrical complication of the shear zones. Within the Czerwone Wierchy Nappe, the minimum value of the mass-loss estimated from a restored cross-section is in the range of 15-50%.