Cinemática de fallas normales menores tardi- y post-Variscas en la sección costera de la ría del Eo (N de España)

Résumé

In this work we target the analysis of low to intermediate dipping minor faults, often extensional, formed in lower Paleozoic metamorphic rocks in northwestern Iberia. All fracturing events from the late stages of the Variscan orogeny onwards were developed in the study area in upper crustal conditions. The attribution of fault rocks and structures to the different fracturing episodes requires, in addition to mapping relations, the establishment of fault kinematics in minor structures. Given the difficulties in the exposure of major fault zones in the area, minor structures are key to unravel the tectonic evolution. Based on the orientation of slip surfaces and other secondary fractures, and map patterns, three main extension directions for the normal faults can be defined. The dominant extension direction is NW-SE, consistent with the activity along the youngest Variscan structures, a few kilometers to the W: the Vivero and the Areoura faults. A second NE-SW extension is consistent with the orientation of faults bounding Permian-Triassic basins further East. A third set of faults, trending N-S, are consistent with the major extension direction during the opening of the Atlantic, common to the W of the study area.