A SW Iberia Indenter? Paleomagnetism and kinematics

Abstract

Mountain belts usually show some sense of curvature in plan view, but not all curvatures are created equal. The term Orocline has a kinematic connotation and defines orogenic curves which are formed by differential vertical axis rotations, concomitant or secondary to their formation, while primary curves depend on geophysical features. The Variscan orogeny, is formed during the late-Carboniferous amalgamation of Pangea, by the collision of Gondwana and Laurussia and it is an example of such a winding mountain belt. A double curve stands out in Iberia, where the coupled Cantabrian Orocline and Central Iberian Curves are found. The kinematics of the latter are not yet clear; however, the former satisfies the kinematic criteria of a secondary orocline. The mechanism of formation for this coupled system is still contested, and often necessitate inconciliable kinematics for southwestern Iberia, where data is lacking. In this paper we solve this data vacuum and shed light on the kinematics of southwestern Iberia. We sampled along the Laurussian South Portuguese Zone, and Gondwanan Ossa-Morena and Almadén syncline, in the central Iberia. Our results show large scale counterclockwise rotations occurring in the late-Carboniferous all throughout the external zones of the Iberian Variscides and Central Iberian Zone. Data from the Almadén syncline show homogeneity in the rotation sense of Iberia and rule out the possibility of coeval formation of the two curves. We propose that the rotations present in Iberia all occur due to a 90º change in the stress field of Pangea in the late-Carboniferous, in agreement with the formation of a Greater Cantabrian Orocline, that extends from south Iberia to Britany (France) and Ireland.