Figure 1. The Ronda mantle shear zones.

(a) Location of the Ronda peridotite massif (Betic cordillera, southern Spain) and its mylonitic complexes, including the study area (modified from Hidas et al.²³). (b) Studied area of a 5-m-thick mylonitic complex of spinel-bearing harzburgite (protolith) with top-to-the-SW kinematics (inset). (c) Detailed view of the strain partitioning between protomylonitic and (ultra)mylonitic spinel-bearing peridotites in the mylonitic complex. (d) Photomicrograph (plane polarized light) of a mylonite layer highlighting very fine-grained anastomosing ultramylonite bands adjacent to pyroxene porphyroclasts. The thin section has been cut in the XZ structural plane, that is, the plane normal to the shear plane and parallel to the shear direction. All ductile horizontal structures are crosscut by post-tectonic serpentine. The thin section is 50 μm thick. Opx=orthopyroxene; Spl=spinel.