Triassic stretching directions in Iberia and North Africa inferred from magnetic fabrics

Abstract

During the Triassic, Iberia and western North Africa displayed a unique situation in relation with the Central and North Atlantic opening and westward expansion of the Tethys. Unravelling the stretching direction in Triassic deposits of the studied area can help in our understanding of this scenario. The tectonic setting is characterized by localized basins with strong thickness variations greatly influenced by previous post-Variscan mechanical discontinuities. In this work, we revise and compile magnetic fabric data from eight Triassic depocentres in terms of defining the stretching direction (i.e. magnetic lineation), resulting from extensional deformation of this period. Data show the importance of the opening of the Atlantic rift as the leading process during the Triassic. Dextral transtension can explain the deflection of the extensional direction observed in most studied depocentres that is caused by the activity of previous major oblique faults.

A reconstruction of Iberia accounting for W-Tethys/N-Atlantic kinematics since the late Permian-Triassic

“…This displacement has been partitioned with extension within the Iberian basins along a NW-directed intra-continental deformation corridor. This is consistent with stretching markers in Triassic rocks in this area (Soto et al, 2019). From 160 to 100 Ma, the northward propagation of the Central Atlantic spreading ridge into the southern North Atlantic resulted in a net left-lateral slip of 245 km and increasing strain rates of up to 9 km.Myr −1 , indicating the southern Ebro boundary became the main tectonic boundary in Iberia, accommodating eastwards displacement of Iberia into the Alpine Tethys region.…”

“…The large rift-related subsidence in the Iberian basins ( Fig. 3B) is kinematically consistent with the stretching lineations documented from Triassic strata (Soto et al, 2019). Ebro is already individualized from Iberia and moved eastwards relative to Iberia and Europe through right-lateral and left-lateral strike-slip movements, respectively.…”

“…During the late Permian-Early Triassic, a first phase of significant tectonic subsidence, up to 500 m, is recorded in the Maestrat basin and on the Iberia paleomargin of the Betic basins (Salas and Casas, 1993;Van Wees et al, 1998;Salas et al, 2001;Hanne et al, 2003;Soto et al, 2019) (Fig. 3B-C).…”

A reconstruction of Iberia accounting for Western Tethys–North Atlantic kinematics since the late-Permian–Triassic

“…It suggests that the transcurrent deformation that results from the eastwards movement of Iberia occurred mainly during the Late Jurassic-Early Cretaceous in northern Iberia along a 100 km scale pull-part or en échelon rift basins formed by the NW-SE-trending Iberian massifs. Indeed, along these massifs, several extensional basins recorded major subsidence and strike-slip deformation during the late-Permian to middle-Cretaceous time interval (Alvaro et al, 1979;Salas et al, 2001;Aldega et al, 2019;Aurell et al, 2019;Soto et al, 2019). However, no geological evidence for lithosphere-scale strike-slip movements has yet been clearly defined in the intra-Iberian basins.…”

“…Moreover, the contribution of pre-Late Jurassic-Early Cretaceous extension phases might have been substantial to the overall crustal attenuation and movements of Iberia (Fig. 1a) (Fernández, 2019;Soto et al, 2019). Indeed, two major geodynamic events, the late-Permian-Early Triassic breakup of Pangea and the opening of the Neotethys and the Late Triassic-Early Jurassic central Atlantic magmatic event preceding the opening of the North Atlantic Ocean are recorded in Iberia and contributed to the finite crustal thinning.…”