Late Paleozoic Iberian orocline(s) and the missing shortening in the core of Pangea. Paleomagnetism from the Iberian Range.

Abstract

Supercontinents are usually interpreted to be single and rigid continental plates. How and when Pangea became a rigid supercontinent is disputed, and age estimations vary from ~330 to ~240 Ma. The Gondwana-Laurussia collision formed the Variscan-Alleghanian belt, the most prominent witness of Pangea’s amalgamation. In Iberia, this orogen draws an “S” shape featured by the Cantabrian Orocline and the Central Iberian curve. The curvature of Central Iberia is particularly evident in Galicia-Tras Os Montes and in a change of trend that it draws in the Aragonese Branch of the Iberian Range. Recent research showed that both curvatures are not coeval and that the Central Iberian curve had to form prior to ca. 318 Ma (i.e. not a secondary orocline). We report paleomagnetic and structural results from Paleozoic rocks in the Santa Cruz syncline (Aragonese Branch of the Iberian Range) that indicate two main vertical axis rotations events: 1) a Cenozoic (Alpine) clockwise rotation of >20˚ and 2) a Late Carboniferous counterclockwise rotation of ~70˚. Once the Cenozoic rotation is restored, the change in structural trend that allegedly evidences the outer arc of the Central Iberian curve disappears. Whereas the Cenozoic rotation is incompatible with a Central Iberian curve, the Late Carboniferous rotation is fully compatible with the Cantabrian Orocline, enlarging the area affected by its counterclockwise rotations and the existence of a non-rigid Pangea until, at least, ~295 M.a