Studio del Bacino Laguna Blanca (Catamarca, Argentina), nell'Altipiano Andino Centrale: telerilevamento ed analisi strutturale

The Laguna Blanca basin is located in the south-central Andes, along the south margin of the Puna plateau. This sector of the Andean chain is characterized by an oblique subduction between the Nazca and South-America plates, allowing a transpressive stress regime. The aim of this thesis is to define the nature of the rhomboidal shaped Laguna Blanca basin, in the frame of general tectonic evolution of the area. According to this aim, a remote sensing analysis was firstly carried out, using images from multispectral sensor (ASTER and Landsat 7 ETM+) and medium resolution Digital Elevation Model (SRTM and ASTER GDEM). Particular attention was given to ASTER image processing, finalized to map different lithologies using false color composites, band ratios (BR), relative absorption band-depth (RBD) and spectral angle mapper supervised classification (SAM). During this processing phase, the high-resolution spectral signatures of samples collected in the field were of fundamental importance. These data were obtained using a Varian-Cary5000R spectrophotometer (with wavelength range from 0.35μm to 2.5μm and 1nm sampling step). The high-resolution spectral signatures were resampled at the ASTER sensor resolution and used to identify the ASTER bands for RB and BDR elaborations. They were also applied for SAM supervised classification, but in this case spectral signature retrieved from specific Region of Interest (ROI), directly derived from the ASTER image, were much more effective in lithology discrimination. Finally image sharpening of Landsat 7 ETM+ images and hill shades of medium resolution DEM allowed to identify the principal tectonic lineaments of the study area. The results of remote sensing analysis, together with the field observations, enable to realize a new geological map of the study area. During the fieldwork I also acquired meso-structural data that were used to retrieve local stress fields through stressinversions methods. The results have shown a general NW-SE horizontal shortening, compatible with the left lateral strike-slip kinematics of the N-S faults bounding the Laguna Blanca basin. On the other hand, a pure extensional regime has been recorded within the basin, although the maximum horizontal shortening holds steadily along a NW-SE trend. All these results, together with macro- and mesoscale morphological and structural evidences support the interpretation of the Laguna Blanca basin as a pull apart basin generated at a releasing stepover along inherited N-S strike-slip master faults. This kinematics, although opposite to the one expected from the general ENE-WSW convergence between the Nazca and the Sud- America plates, is consistent with a transpressive deformation developed on an “hot” orogen, overthrusting a steep subducting plate, bounded southward by a “cold” sector related to a shallow subduction.