Estudo do comportamento físico das diferentes fácies do granito Bannach, Suíte Jamon, Domínio Rio Maria

Abstract

The Paleoproterozoic Bannach Granite belongs to the Jamon Suite, Rio Maria Domain, the south-ern portion of the Carajás Province. Geologic studies indicate that texture and composition of the different facies of this granite are responsible for the geomorphological control of this batholith, and there is no work on the qualification of physical parameters that justify this hypothesis. Thus, this research aims to determine the physical characteristics involving porosity, density, compres-sional velocity and shearing velocity S1 and S2, besides geomechanical tests to evaluate the re-sistance of these rocks. The values of density (2.52 to 2.62 g/cm³), porosity (<1.85%) and com-pressional velocity (usually between 5500 and 6000 m /s) demonstrate that they are compatible with those expected for granites. The point load tests showed that the resistance index of the sam-ples with coarse texture (ABMzG e LMzG) have low resistance (2,96 a 4,70 MPa), in contrast to the fine-grained rocks (LMzM e LMzF) which are more resistant (5,31 até 9,85 MPa), justifying the geomorphological behavior of the textural facies of Bannach Granite. Since the coarse facies due to the low resistance and high susceptibility to physical weathering and erosion, tend to occupy topographically flattened and plane area, different from the fine-grained facies (LMzM e LMzF), which have low resistance and less susceptible to erosion, resulting in ridge and hills of the Bannach Granite. The ration of shear wave’s velocities S1 and S2 oscillate in values close to one, confirming the isotropic nature of Granite Bannach, previously suggested in the fieldwork. The fusion between the SRTM data and the aerogamma-ray spectrometry (thorium channel) revealed that in areas of plane relief; dominate coarse-grained rocks with low radiometric values and resistance, in contrast to areas that are ridge and hills, which are constituted by fine-grained rocks, more resistant and high radiometric intensity