Multi-scale Analysis of the Mylonitized Giant Quartz Veins of the Cap de Creus and Canigó Massifs (Pyrenees)

Quartz veins with widths ranging from meters to hundreds of meters and lengths from tens of meters to kilometers, known as Giant Quartz Veins (GQVs), are ubiquitous in orogenic belts worldwide. These veins are very useful to gain understanding of fluid flow, quartz precipitation, and deformation mechanisms and also to unravel the geochemical history of their host rocks. The present work is dealing with multi-scale analysis (from orogen-to microscopic-scales) of the mylonitized GQVs encountered in the Cap de Creus and Canigó Massifs, Eastern Pyrenees, SW Europe. Despite being hosted in variable rocks and emplaced along different structures, the studied GQVs share various similar features: (1) the development of silicification halos, (2) evidence of different mechanisms of quartz growth through host rock replacement, host rock dissolution related to the opening of cm-wide vein networks, and aggregation of multiple crack-seal veins, and (3) a strong structural control on their emplacement. The GQVs postdate the development of regional cleavages but are affected by a mylonitic/phyllonitic foliation, showing evidence of deformation by dislocation creep and a wide range of microscopic shear sense indicators. The pre-existing structures along which the Roses GQV was formed vary even within hundreds of meters, from a brittle thrust fault to a mylonitic band. In the Esquerdes de Rojà GQV, an incipient to well-developed low temperature mylonitic fabric is present along more than 15 km, and grain-size reduction is mainly achieved along cataclastic bands. These features can be representative of the more than 700 GQVs that have been mapped in the Pyrenees.