The ESCI-N2 deep seismic reflection profile: a traverse across the Cantabrian Mountains and adjacent Duero basin

The ESCI-N2 deep seismic reflection profile images the crustal structure of the transition between the Cantabrian Mountains and the Duero foreland basin. It was traced perpendicular to the Alpine structural directions to investigate the role of the Alpine deformation in the tectonic evolution of the northern margin of the lberian Peninsula. Besides the very well imaged sedimentary cover of the Duero basin, the first outstanding feature of the profile is the change in the intensity and character of the reflectivity between shallower and deeper levels of the crust. The reflectivity is weaker in the upper 6 s (TWT), whereas it increases its intensity abruptly below this level. The most remarkable feature observed in the upper crust is represented by discontinuous but line-up, n01th-dipping reflections interpreted as Alpine thrusts. These thrusts merge into the 6 s level, that can be inteipreted as a mid-crustal detachment. The southwards thrusting of severa! crustal slices along this thrusts gave rise to the tectonic uplift of the Cantabrian Mountains. A reflective lower crust with a band of high reflectivity at its base was imaged in ESCI-N2 profile. The Moho is situated at the base of this reflective zone, that changes its attitude from horizontal beneath the' Duero basin to north-dipping beyond the mountain front, with the reflection Moho deepening from 12 to 16 s (TWT). The topography of the Moho implies a downward bending of the "lberian" lower crust that is interpreted as inducted by the indentation of a wedge of the "Cantabrian Margin" lower crust in the middle of the "lberian" crust. This results in a delamination mechanism that splits the lberian crust apart with the lower crust subducting n01thward and the upper crust detaching and uplifting to build up the Cantabrian Mountains.