Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

Abstract

International audienceThis paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record

Comment on “Reconstruction of the Exhumed Mantle Across the North Iberian Margin by Crustal‐Scale 3‐D Gravity Inversion and Geological Cross Section” by Pedrera et al.

“…One of the consequences of preserving the Mesozoic exhumed mantle domain in the present‐day crustal section across the Basque‐Cantabrian Basin proposed by Pedrera et al () is that their sequential restoration implies a total shortening of only 34 km since the Late Cretaceous. This is 2.5 to 5 times smaller than the shortening predicted by different plate kinematic models or deduced from geological reconstructions by other authors in a wide range of sections along the Pyrenean‐Cantabrian belt (e.g., Macchiavelli et al, ; Rosenbaum et al, ; Teixell et al, , and references therein; Vissers & Meijer, ). Although it is possible that those kinematic models and other reconstructions might have overestimated the orogenic shortening, it is hardly acceptable to present such a divergent result while restricting the discussion to this failed argument: “Such lower shortening rates across the eastern part of the Cantabrian Mountains were possibly caused by the coeval inversion of the Cameros Basin, caused by the thrust front of the Iberian Chain.…”

Formation of the Iberian‐European Convergent Plate Boundary Fault and Its Effect on Intraplate Deformation in Central Europe

“…The complexity in the extensional history of the Bay of Biscay and the uncertainties in the timing and distribution of shortening in response to plate convergence make it problematic to directly transfer our findings from the Pyrenean realm to the Bay of Biscay area without additional data. Independently, the underthrusting of Iberia beneath the North Iberian Margin can be traced until ~6°–7°W and appears in continuity with the underthrusting of Iberia beneath the Pyrenees (Figure ; Pedreira et al, , ; Roca et al, ; Teixell et al, ). We therefore suggest that the fault system that allowed the underthrusting of Iberia beneath the North Iberian Margin represents the westward continuation of IEPB fault.…”

“…In the following, we focus on the precollisional to early collisional evolution of the Pyrenees and summarize key information that provides insights into the tectonics around the onset of Africa‐Iberia‐Europe convergence. For further information on the Pyrenean orogeny we refer to the recent literature (Angrand et al, ; Grool et al, ; Labaume et al, ; Mouthereau et al, ; Teixell et al, ; Tugend et al, ; Vacherat et al, ).…”

Unraveling the Mesozoic and Cenozoic Tectonothermal Evolution of the Eastern Basque‐Cantabrian Zone–Western Pyrenees by Low‐Temperature Thermochronology

“…It is widely accepted that the onset of convergence in the Pyrenees s.s. occurred in the Late Cretaceous, at ~83–84 Ma (Macchiavelli et al, ; Teixell et al, , and references therein). At that time, however, oceanic crust was being created in the center of the Bay of Biscay (up to chron A33o, 80 Ma; e.g., Sibuet et al, ), implying simultaneous lithospheric extension toward the west.…”

“…Around the SE corner of the present‐day Bay of Biscay, the Basque‐Cantabrian basin developed as one of the most strongly subsiding basins of the Iberian periphery during the Aptian‐Cenomanian (García‐Mondéjar et al, ; Rat, ). Alpine convergence resulted in the inversion of these hyperextended crustal domains with intracontinental collision in the Pyrenees (Beaumont et al, ; Muñoz, ; Teixell et al, , ), whereas shortening and uplift of the Mesozoic passive margin farther west created a coastal range: the Cantabrian Mountains (Alonso et al, ; Gallastegui et al, ; Pedreira et al, ; Pulgar et al, ; Quintana et al, ). Although along‐strike differences in the orogenic style are evident, there is structural continuity between both mountain ranges (e.g., Pedreira et al, ).…”