Analyzing Strain Localization, Kinematic Partitioning and Fluid Flow in the Pulo Do Lobo Metasedimentary Rocks Along the Southern Iberian Shear Zone, Andalucia, Spain

Abstract

The Southern Iberian Shear Zone is a regional scale ductile shear zone that placed Beja-Acebuches metabasites over metapelite and quartzite rocks of the Pulo do Lobo Formation in a transpressional deformation with components of thrust and left-lateral movement. This project evaluates factors that contributed to strain localization at a variety of scales within the Pulo do Lobo formation, including lithologic variations, microstructures, and fluid flow. Additionally, microstructural data are used to test whether kinematic partitioning accompanied strain localization. Grain scale asymmetric indicators of sigma-type clasts, S-C fabrics, and asymmetric folds indicate dominant thrust motion. Strain intensity and metamorphic grade increase towards the shear zone. Within about 170 m, relatively low grade slates with regional slaty cleavage transition to garnet-zone amphibolite metamorphism and closely-spaced, strong schistose foliation. Microstructures indicate a gradual increase in crystal-plasticity towards the shear zone that likely allowed for gradual strain increase. However, fluid interaction promoted additional deformation mechanisms near the shear zone including diffusive mass transfer (most prevalent