Strain analysis from calcite e-twins in the Cameros basin, NW Iberian Chain, Spain

Abstract

Calcite twins and c-axes from sparry grains that fill micro-veins were used to unravel the deformational history of the Cameros Massif, an inverted Mesozoic sedimentary basin located in the northwestern part of the Iberian Chain (Spain). Calcite c-axis and microvein orientations indicate the existence of two extension directions (NW–SE and NE–SW) during the basin formation probably related to the slip along two syn-sedimentary faults. Calcite e-twins were developed only in micro-veins from the frontal ramp area, i.e. in the northeast side of the basin, where the stresses were higher during the basin inversion. Twin analysis yields three different orientations (NW–SE, E–W and NE–SW) for the minimum horizontal extension direction (i.e. Shmax under coaxial conditions), which suggests that the basin inversion was developed through several thrusting episodes, during which the frontal and lateral ramps of each one of these episodes are interchanged. Moreover, the perpendicularity between c-axes and the minimum extension directions suggests that the basin inversion was produced along the same faults that controlled the basin formation. The minimum extension directions deduced from e-twins are also consistent with the shortening directions established previously for the Tertiary evolution of the Iberian Chain, which suggest that the basin inversion involved several tectonic events during the Neogene. These results show the advantage of the combined c-axis and e-twins analysis to unravel deformational and kinematic histories.