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-Trás-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 nonrigid Pangea until, at least,~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.

Basement‐Cover Relationships and Their Along‐Strike Changes in the Linking Zone (Iberian Range, Spain): A Combined Structural and Gravimetric Study

“…Taking that into account, restored cross sections in the study area allow the estimation of horizontal shortening values that are strongly variable across the eastern North Branch of the Iberian Range (~11 km in Cross Section 1, Figure a, and ~3 km along Cross Section 2). These values roughly indicate an eastward shortening decrease in the study area that is in agreement with recent paleomagnetic investigations revealing moderate clockwise rotations in the North Branch (~22° clockwise; Pastor‐Galán et al, , to the west of the study area). These magnitudes will have a negligible impact in the shortening estimates (Oliva‐Urcia & Pueyo, ; Sussman et al, ).…”

“…Nevertheless, these restorations underestimate shortening values where sections traces are oblique to the main transport direction (North Branch of the Iberian Range and Catalan Coastal Ranges) and moderate to important shortening takes place out‐of‐plane of the cross sections. Shortening underestimates caused by the obliquity of the transport direction (Cooper, ) and/or the occurrence of vertical axis rotations (as it is the case in some sectors of the North Branch of the Iberian Range; Pastor‐Galán et al, ) may be later on corrected using existent approaches (Pueyo et al, ).…”

The enigmatic curvature of Central Iberia and its puzzling kinematics

“…The most relevant new data regarding the kinematics of the Central Iberian curve is the paleomagnetic study from the Iberian Ranges Pastor-Galán et al, 2018).…”

Avalonia, get bent! Paleomagnetism from SW Iberia confirms the Greater Cantabrian Orocline

“…2a) part of the Central Iberian curve's hinge (e.g. Shaw et al, 2012), but recent studies proved a Cenozoic origin for such deflection (Calvín et al, 2014;Pastor-Galán et al, 2018;Izquierdo-Llavall et al, 2018). The available late Carboniferous kinematic data from central Iberia do not allow for a coeval formation of both curvatures (e.g.…”