Inversion of the north Iberian hyperextended margin: the role of exhumed mantle indentation during continental collision

Abstract

Critical gravity and magnetic data suggest the presence of a continuous zigzag exhumed mantle body inside the attenuated crust of the north Iberia continental margin. We propose that this body greatly conditioned the structural domains of the Cantabrian–Pyrenean fold-and-thrust belt during their evolution from hyperextension in Early Cretaceous times to shortening and inversion during the Cenozoic. This may be seen as a new line for cross-section construction and balancing, because previous cross-sections do not incorporate comparable volumes of exhumed mantle. Five structural cross-sections, constrained by the results of 3D gravity inversion, feed our discussion of the complexities of the doubly vergent Pyrenean orogen in view of the inversion of a precursor hyperextended rifted margin. In all sections, crustal rocks underthrust the lithospheric mantle in the hyperextended region, supporting that the near-surface exhumed mantle lithosphere acts as a more rigid buttress, allowing weaker continental material to be expelled outwards and upwards by thrusting during the Alpine collision; thus giving rise to two uplifted crustal triangular zones at the boundaries with the exhumed mantle. Contractional slip is localized in lithospheric-scale thrusts, which in turn reactivate parts of the extensional system. The NE–SW transfer zones that offset the rift therefore behave as compartmental faults during the orogenic phase. The amount of shortening increases from 34 km in the Cantabrian Cordillera, where the Basque–Cantabrian Basin partially preserves its original extensional geometry, to 135 km in the nappe stack of the central Pyrenees.

Regional Crustal Imaging by Inversion of Multimode Rayleigh Wave Dispersion Curves Measured From Seismic Noise: Application to the Basque‐Cantabrian Zone (N Spain)

“…Our results disagree with recent interpretations that consider the presence of mantle in situ at <10 km depth approximately beneath the area of the BCMA in Zone 2 (García‐Senz et al., 2019; Pedrera et al., 2017). These authors argue that the mantle was exhumed to the base of the sedimentary pile in the Basque‐Cantabrian Basin during the Mesozoic and that the geometry of this mantle uplift was only subtly modified by the orogenic event that gave rise to the Pyrenean‐Cantabrian Mountain belt during the Cenozoic.…”

“…(2018) (“magnetic” model, left, see Table S1 in the supporting information) and from the gravity model of García‐Senz et al. (2019) (“gravity” model, right, see Table S2 in the supporting information) and their associated dispersion curves. Red lines show the outcome of the nonlinear inversion using the “gravity” and “magnetic” models as initial models.…”

“…However, there are some inconsistences between the magnetic properties and the densities employed by the authors of the exhumed mantle model (see the comment by Pedreira et al., 2018), so we derived two 1D shear velocity models to use as starting models: one from the magnetic model by (Pedrera et al., 2017, 2018) and the other from the gravity model by García‐Senz et al. (2019) (for a detailed description of the derivation of these models, please see Text S5 and Tables S1 and S2 in the supporting information). We then used these models as initial solutions in a nonlinear inversion of the phase velocities compiled at node 1575, which is located above the mantle uplift zone proposed by these authors.…”

Unravelling the architecture and evolution of the inverted multi-stage North Iberian-Bay of Biscay rift

“…Extreme crustal thinning and mantle exhumation have been well-documented from Aptian to Cenomanian in north Iberia (e.g., Jammes et al, 2009;Roca et al, 2011;Masini et al, 2014;Pedrera et al, 2017;Quintana et al, 2015;Tugend et al, 2015;Cadenas et al, 2018;DeFelipe et al, 2019;García-Senz et al, 2019;Saspiturry et al, 2019;Lescoutre & Manatschal, 2020). Northdipping extensional detachment faults led to the development of the Biscay rift system (this study), the Basque-Cantabrian Basin (e.g., Quintana et al, 2015;Pedrera et al, 2017;Tavani et al, 2018;DeFelipe et al, 2019;García-Senz et al, 2019) and the Mauleón Basin (e.g., Jammes et al, 2009;Masini et al, 2014;Saspiturry et al, 2019;Lescoutre & Manatschal, 2020). The link and the spatiotemporal evolution of these hyperextended systems is still unresolved.…”

3D reconstruction of syn-tectonic strata in a salt-related orogen: learnings from the Llert syncline (South-central Pyrenees)

“…5). In the study area, the syn-compressional succession is subdivided into the Campo Breccias and the Mascarell Turbidites members (Ardèvol et al, 2000;García-Senz, 2002;García-Senz et al, 2019b;Garrido-Mejías, 1973;Robador and Zamorano, 1999;Souquet, 1967;van Hoorn, 1970). The Campo Breccias Member consists of limestone breccias alternating with thinly-bedded sandy turbidites, which onlap the Campo unconformity ( Fig.…”