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

Jurewicz E.

Acta Geologica Polonica

2006

Vol. 56, no. 2

159-170

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%.

The Zadnie Kamienne "ravenous" shear zone (High-Tatric Nappe) - conditions of deformation

Jurewicz E., Słaby E.

Geological Quarterly

2004

Vol. 48, No 4

371--382

The Zadnie Kamienne shear zone is a high-angle Riedel type shear zone (R'), exhibiting an antithetic sense of displacement, which may have developed synchronously with the nappe-thrusting of the Giewont Unit (High-Tatric Nappe). The amount of displacement along this zone is very low and does not explain the very intense deformation, which is of the same character as that at the base of the Giewont Unit (mylonitization, stylolitization and vein forming). The explanation of this phenomenon lies in the multiple activity of this zone, the change of the direction of movement and the important role of pressure solution in hydrothermal conditions responsible for dissolution creep, mass loss and stress relaxation. This kind of shear can be referred to as a "ravenous" shear zone. Neo-forming minerals accompanying these processes were applied as a temperature gauge. Simultaneous growth of albite and adularia indicates a temperature of about 350 degrees C. Chlorites accompanying them occur in two thermal episodes, the first of which indicating a similar temperature (292-357 C).