Role of rift-inheritance and segmentation for orogenic evolution: example from the Pyrenean-Cantabrian system

Abstract

The Basque-Cantabrian junction corresponds to an inverted rift accommodation zone at the limit between the former hyperextended Pyrenean and Cantabrian rift segments. The recognition of an inherited rift segment boundary allows to investigate the reactivation associated with large-scale rift segmentation in an orogenic system. We use criteria from published field observations and seismic data to propose a new map of rift domains for the Basque-Cantabrian junction. We also provide balanced cross-sections that allow to define the along-strike architecture associated with segmentation during rifting and subsequent Alpine reactivation. Based on these results, this study aims to characterize and identify reactivated and newly formed structures during inversion of two rift segments and its intermitted segment boundary. It also aims to describe the timing of thin-skinned and thick-skinned deformation associated with the inversion of segmented rift systems. During convergence, two phases have been recognized within the rift segment (eastern Mauléon basin). The Late Cretaceous to Paleocene underthrusting/subduction phase was mostly governed by thin-skinned deformation that reactivated the former hyperextended domains and the supra-salt sedimentary cover. The Eocene to Miocene collisional phase, controlled by thick-skinned deformation that took place once necking domains collided and formed an orogenic wedge. At the rift segment boundary, the underthrusting/subduction phase was already controlled by thick-skinned deformation due to the formation of shortcutting thrust faults at the termination of overlapping V-shaped rift segments. This led to the formation of a proto-wedge composed of the Basque massifs. We suggest that this proto-wedge is responsible for the preservation of pre-Alpine structures in the Basque massifs and for the emplacement of subcontinental mantle rocks at a crustal level beneath the western Mauléon basin. These results argue for a first order cylindrical orogenic architecture from the Central Pyrenean segment to the Cantabrian segment (up to the Santander transfer zone) despite rift segmentation. They also highlight the control of 3D rift-inheritance for the initial phase of orogenic evolution and for the local architecture of mountain belts.

Basement‐Cover Decoupling During the Inversion of a Hyperextended Basin: Insights From the Eastern Pyrenees

“…This tectonic process is in agreement with recent studies promoting large displacements of rifted basins along inherited decoupling layer (Gómez-Romeu et al, 2019;Labaume & Teixell, 2020). Rift-related inheritances (crustal structures and rheology) may fundamentally control the development and the finite structure of orogens by controlling the depth of the decoupling layer and its propagation (e.g., Gómez-Romeu et al, 2019;Lacombe & Bellahsen, 2016;Lescoutre & Manatschal, 2020;Tavani et al, 2020;Tugend et al, 2014). Inversion of the hyperextended domains depends of the depth of the efficient decoupling layer.…”

“…The tectonic history of the eastern Pyrenees as discussed in this paper thus shows the succession of two periods of the contractional deformation that led to the full inversion of the rifted margins. Other sections, further west, except for the Basque-Cantabrian basin with the Nappe des Marbres (Ducoux et al 2019;Lescoutre & Manatschal, 2020), show a narrower IMZ where most units are pinched and vertical, thus obliterating the details of the shortening history. The Agly section and the Nappe des Marbres sections are thus key to unravel the early stages of the Pyrenean shortening with two stages, a first thin-skinned episode with décollement of the basin above the Triassic evaporites and a second thick-skinned episode leading to the present-day structure.…”

“…Then, two hypotheses can be proposed: (1) the Bas-Agly syncline may be the eastern equivalent of the St-Paul-de-Fenouillet Basin with a higher metamorphic grade and the two basins were carried along the basal décollement in Upper Triassic evaporites until they got into close contact; (2) alternatively, the Bas-Agly syncline may be the western termination of a rift segment developing eastward, if we consider the eastern termination of Pyrenees as a relay or accommodation zone where the rift axes are shifted. The Boucheville and Bas-Agly synclines may corresponded to V-shaped terminations of two rifted basins, as the western Pyrenees for instance (e.g., Lescoutre & Manatschal, 2020) and corresponds instead to a displaced outlier of a more internal and hotter unit where high temperature is due to mantle exhumation as elsewhere in the NPZ.…”

Nature, Origin, and Evolution of the Pyrenean‐Cantabrian Junction

“…The Jurassic succession that continues parallel to the Leiza fault all along its trace to the south is folded into a syncline (Figure 8), which eastern termination is visible east of the village of Ziga, where the mantle rocks crop out (Figure 9a). East of this termination the Aldudes massif represents a large, west-plunging, E-W striking anticlinal in the hanging wall of the Roncesvalles thrust to the south (Lescoutre & Manatschal, 2020) and the Aldudes fault to the north-west, as evidenced by the continuous outcrop of lower Triassic sandstones along its southern, northern and western boundaries (Figure 9). On a map view, the limit between the Mesozoic cover of the Nappe des Marbres and the underlying Lower Triassic sandstones of the Aldudes massif is curved, following the limits of the large Aldudes massif anticlinal and suggesting that both the basement and the sedimentary cover have been folded during convergence and subsequently eroded (Figure 8).…”

Crustal Accretion and Chain Building of an Inherited Passive Margin: Insights From the Western Southern Alps

“…An increasing interest has been recently focused in literature on the role of lithospheric extension and inheritance in affecting later orogeny (e.g., Roda et al, 2019;Festa et al, 2020;Lescoutre and Manatschal, 2020;Tavani et al, 2021); nonetheless, most of the structural interpretations of the orogenic chains worldwide are still based on the old concepts arising from the hydrocarbons prospection studies and traditionally divided into thick vs thin skinned models. In more recent years, considering the whole scale orogen, continental lithospheric contractional styles have been rather conceptualized as ranging between two end-members scenarios that describe the distribution of strain with depth, down to the lithosphere boundary, and resulting in different amounts and geometries of crustal accretion in orogenic wedges: detachment-dominated, and ramp-dominated scenarios (Butler and Mazzoli, 2006).…”