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.
Highlights
The Cantabrian Mountains constitute an E–W-oriented range that extends more than 250 km and is the western extension of the Pyrenean range (Fig. 1)
The Alpine history is directly related to the post-Variscan evolution of the North Iberian Margin, which started by a Permo-Triassic rifting stage that was followed by an approximately N–S extensional episode, triggered by the opening of the Atlantic Ocean and the Bay of Biscay during Late Jurassic and Early Cretaceous times
This paper focuses on the N–S deep crustal structure of the southern part of the Cantabrian Mountains and the transition to the adjacent Cenozoic Duero basin imaged in deep seismic reflection profile ESCIN-2
Summary
The Cantabrian Mountains constitute an E–W-oriented range that extends more than 250 km and is the western extension of the Pyrenean range (Fig. 1). The ESCIN and MARCONI programs and other related projects were planned to study the deep crustal structure and evolution of the Cantabrian Mountains and continental margin from deep seismic reflection and refraction/wideangle data (Pérez-Estaún et al, 1994; Pulgar et al, 1995, 1996; Álvarez-Marrón et al, 1996, 1997; Gallastegui et al, 1997; Ayarza et al, 1998; Fernández-Viejo et al, 1998, 2000; Gallastegui, 2000; Gallastegui et al, 2002; Fernández-Viejo and Gallastegui, 2005; Fernández-Viejo et al, 2011, 2012) These studies showed that the deformation of the area due to the Alpine compression affected the shallow crustal levels and the deeper ones. A geological cross section of the area has been constructed, integrating published data (ESCIN-2, a refraction profile and a conductivity model) with a depth model of ESCIN-2 obtained by 2-D seismic modelling, a gravity model coincident with ESCIN-2, and all geological/geophysical data available (wide-angle/refraction and magnetotelluric (MT) data)
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