Sense of nappe emplacement from quartz c-axis fabrics; an example from the Betic Cordilleras (Spain)

Abstract

Preferred crystallographic orientation patterns (fabrics) in zones of ductile deformation beneath nappes are a potentially useful indicator of the sense of nappe translation. Quartz c-axis fabrics from a shear zone beneath the pile of Higher Betic nappes in the Betic Cordilleras (Spain) have distinctly asymmetric topologies, revealed by constructing a fabric skeleton. These skeletons closely resemble those produced by computer simulations of quartz fabric development basedon Taylor-Bishop-Hill theory. The fabric asymmetry indicates a northerly sense of transport for the nappes, consistent with field evidence from the same area. Analyses of both c- and a-axis fabrics based on asymmetric intensity distributions within the fabric give equivocal results, and may reflect the presence of earlier preferred orientation patterns, predating nappe emplacement.