Rotación de bloques en sistemas de fallas de desplazamiento lateral-cuencas tensiónales

Abstract

Strike-slip motion along systems of lateral faults with discontinuities (en échelon or sharp bends) results in extensión and subsidence at releasing bends or in uplift and deformation at restraining bends. The resulting structures are known as pull-apart basins and pressure ridges, respectively (or simply pull-apart structures, for short).Pull-apart struetures are eommon at transform plate boundaries and in intraplate tectonic settings such as the San Andrés - Gulf of California right-Iateral transform system, the Polochic-Motagua left-lateral transform system or along central Mexico (Trans--Mexican vo\canic belt). Despite the widely varying tectonic settings and scales, pull-apart struetures are eharacterized by a remarkably. constan t geometry, with generally rhombus-like shapes and a half-length to width ratio of about 1.6. A simple mechanism to account for the origin and cvolution of pull-apart structures is proposed and discussed; it involves block rotation as the main factor in the origin and evolution. The relationships examined al10w us to discuss briefly similar relations involved in widely different fields sueh as those of spiral growth patterns of plants and animals, those used in the design of paintings and buildings, and those arising from geometric progressions (Fibonacci series); the relationship found for the halflength to width ratio of pull-apart structurcs (the so-callcd golden section in Arts and Architecture) also arises in certain chaotic systems where randomness presents an underlying geomctric form, and simple dcterministic systems which despite containing few elements may still generate random behaviour (i.e. chaos), although they suggest causal relationships.