Evolution of microstructure and texture in a small-scale hightemperature marble shear zone from the Ossa-Morena Zone (Iberian Variscan Belt): Microstructures of high-temperature marble shear zone

Abstract

This research investigates microstructures and crystallographic preferred orientation in a high-temperature Variscan small-scale shear zone within marbles from the south-western Ossa-Morena Zone (Iberian Variscan Belt). Quantitative microstructural analysis, and crystallographic preferred orientation data obtained via neutron diffraction and electron backscatter diffraction mapping allowed to infer the deformation mechanisms and active slip systems. The primary S2 foliation, formed during the Variscan D2 deformation phase, is characterized by high-temperature grain boundary migration recrystallization mechanism, coupled with intracrystalline slip on the c(0001)<-12-10> system. Ductile shear zone development, marked by a coarse-grained microstructure with pronounced shape preferred orientation parallel to the shear plane, involved both high-temperature grain boundary migration recrystallization and intracrystalline dislocation creep, accommodated by f{-1012} <10-11> and r{10-14} <-2021> slip systems. These results indicate a high-temperature extensional origin for the S2 foliation and the shear zone formation during the D2 deformation event of the Ossa-Morena Zone, linked to thermal effects from the Beja Igneous Complex plutonism and regional partial melting driven by asthenosphere upwelling (~353–335Ma)