PALEO-STRESS AND STRAIN AND VERTICAL-AXIS ROTATION PATTERNS ACROSS THE PAMPEAN FLAT-SLAB REGION

Minor fault, anisotropy of magnetic susceptibility (AMS), and paleomagnetic data for over 200 sites from Triassic, Cretaceous, and syntectonic redbeds located across the Aconcagua fold-thrust belt, Precordillera, and into the foreland thick-skin Sierras Pampeanas belt above the Pampean flat-slab segment in Argentina have revealed systematic regional shortening patterns and local complications. Paleo-stress and strain directions estimated for early-phase minor faults record early layer-parallel shortening (LPS) at high angles to local structural trend, ranging from SE- to NE-directed around curved fold-thrust traces, with additional variations near tear faults and oblique ramps that appear partly controlled by pre-existing basement heterogeneities and reactivation of Triassic and Cretaceous rift basins. Later-phase minor faults developed during large-scale fold growth, tightening, and thrust fault propagation. AMS ellipsoid shapes vary from near oblate with a weak Kmax lineation parallel to intersection of a subtle LPS fabric with bedding, to triaxial to prolate with a strong Kmax parallel to the local fold axis, and with Kmin acute to bedding on steep fold limbs, interpreted to record protracted development of shortening fabrics during fold tightening. Preliminary analysis of paleomagnetic data has revealed significant local vertical-axis rotations, with ongoing work designed to test for systematic regional rotations, along with ongoing work to evaluate differences in paleo-stress patterns across the transition from flat-slab to normal subduction.