Quantification of finite strain in the Pyrenean Slate Belt; a first assessment using Rf/Φ method

Abstract

Strain analysis has been carried out on (micro)conglomeratic Cambro-Ordovician sediments from the Pallaresa area (Axial Zone of central Pyrenees). Twenty strain ellipsoids have been determined. After correction for refolding and faulting a bulk finite strain ellipsoid for the area was calculated. This ellipsoid has k-value 3.43 and low axial ratios (X/Y = 1.24, Y/Z:1.07). The ellipsoid has a long axis (X) plunging steeply NE, an intermediate axis (Y) parallel to the gently WNW plunging mean fold axis of the area, and a nearly horizontal south plunging short axis (Z). The shortening direction (Z) is normal to the steep N-NNE dipping cleavage. During deformation the sediment pile in the area must have undergone vertical tectonic thickening by factor 1.15. It is argued that this value is a minimal estimate and inhomogenous deformation must be taken into account.