Late Paleozoic Iberian Orocline(s) and the Missing Shortening in the Core of Pangea. Paleomagnetism From the Iberian Range

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 similar to 330 to similar to 240Ma. 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. 318Ma (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 degrees and (2) a late Carboniferous counterclockwise rotation of similar to 70 degrees. 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 nonrigid Pangea until, at least, similar to 295 Ma. Plain Language Summary Supercontinents like Pangea are thought to be rigid and stable in its interiors. It is not clear, however, when the supercontinents achieve its final rigid and sturdy form. There is a debate on when Pangea became a rigid supercontinent; some people argue that it happened as soon as 330 million years ago and others as recently as 240. The Iberian peninsula witnessed all this process, and today, we still can see the relic of the mountain range formed at that time with an S shape. Recent research showed that both north and south curvatures did not form coevally and that the southern curve formed before 318 Ma. We report paleomagnetic and structural results from Paleozoic rocks in the Aragonese Branch of the Iberian Range that indicate that the change in trend that allegedly evidences the southern curve of this S shape is a much later effect of Alpine tectonics. Altogether, the results show that Pangea was not rigid until at least 290 million years ago.