Alpine tectonic wedging and crustal delamination in the Cantabrian Mountains (NW Spain)

Abstract

Abstract. The Cantabrian Mountains have been interpreted as a Paleozoic basement block uplifted during an Alpine deformation event that led to the partial closure of the Bay of Biscay and the building of the Pyrenean range in the Cenozoic. A detailed interpretation of deep seismic reflection profile ESCIN-2 and the two-dimensional seismic modelling of the data allowed us to construct a N–S geological cross section along the southern border of the Cantabrian Mountains and the transition to the Duero Cenozoic foreland basin, highlighting the Alpine structure. The proposed geological cross section has been constrained by all geophysical data available, including a 2-D gravity model constructed for this study as well as refraction and magnetotelluric models from previous studies. A set of south-vergent thrusts dipping 30 to 36° to the north, cut the upper crust with a ramp geometry and sole in the boundary with the middle crust. These thrusts are responsible for the uplift and the main Alpine deformation in the Cantabrian Mountains. A conspicuous reflective Moho shows that the crust thickens northwards from the Duero basin, where subhorizontal Moho is 32 km deep, to 47 km in the northernmost end of ESCIN-2, where Moho dips to the north beneath the Cantabrian Mountains. Further north, out of the profile, Moho reaches a maximum depth of 55 km, according to wide-angle/refraction data. ESCIN-2 indicates the presence of a tectonic wedge of the crust of the Cantabrian margin beneath the Cantabrian Mountains, which is indented from north to south into the delaminated Iberian crust, forcing its northward subduction.

Ambient noise tomography of the southern sector of the Cantabrian Mountains, NW Spain

“…In the ESCIN-2 profile, this fault zone is marked by the presence of two parallel north-dipping bands of reflectors (Fig. 10c) that have been interpreted as crustal scale thrusts (Gallastegui 2000;Gallastegui et al 2016). From our results, it may be estimated that the reflectivity of both bands can be associated with the limits of the shear zone of the thrust, or alternatively correspond to two different structures.…”

“…10(b), depicts the duplication of the crust under the Cantabrian Mountains, the northern half of the study area. The elevated high-velocity block in both cross-sections can be associated with the uplifted Cantabrian margin middle crust, which is expected to be present at 4-5 km depth (Gallastegui et al 2016). The limit between this block and the southern one is marked in the western cross-section (Fig.…”

“…The deep seismic reflection profile ESCIN-2, Fig. 10(c) (Pérez-Estaún et al 1994;Pulgar et al 1995Pulgar et al , 1996Fernández-Viejo et al 2000;Gallastegui 2000;Fernández-Viejo & Gallastegui 2005;Gallastegui et al 2016), located 50 km to the east from the position of the crosssection of Fig. 10(a) and in the same location as Fig.…”

“…(b) The north-south vertical profile located in the same position as the ESCIN-2 profile. (c) Coherency filtered stack section of ESCIN-2 deep seismic reflection profile (adapted from Gallastegui et al 2016). The arrows signal the reflectivity associated with the frontal thrust of the Cantabrian Mountains in the north and to the base of the Duero basin in the south.…”

Potential influence of Mesozoic and Tertiary tectonics on the evolution of European Hepialidae (Lepidoptera)

“…The Cantabrian Mountains extend along the Atlantic coast, and although topographically separated from the Pyrenees by the Basque-Cantabrian basin, they are part of the same Cenozoic alpine deformation. Uplift progressed westwards from the Pyrenees to the Cantabrian Mountains where a north-south plate convergence took place and partially closing the Bay of Biscay to the north (Gallastegui et al 2016).…”