The unevenness of the north Iberian crustal root, a snapshot of an elusive stage in margin reactivation

Abstract

Crustal roots are identified in collision chains worldwide. Frequently mirroring the summits of mountain systems, they elegantly encapsulate the concept of isostasy. The rugged topography of northern Iberia results from convergence with the European plate during the Alpine orogeny that formed the Pyrenean-Cantabrian mountain range. From east to west, the range comprises three distinct parts: the Pyrenees, the Basque Cantabrian region, and the Cantabrian Mountains. The identification of the Pyrenean root in the 1980s and the observation of a similar geometry beneath the Cantabrian range in the 1990s gave place to the current view of crustal thickening as a continuous feature, resulting from the northward subduction of Iberian crust. Recent developments in rift architecture have delivered a complex rifting template for the area prior to convergence, and contrasting views based on two-dimensional restorations have led to a debate over its evolution. A crucial geophysical constraint is Moho topography. Using two different data sets and techniques, we present the most accurate Moho surface to date, evidencing abrupt changes throughout the orogen. The complexity of hyperextended margins underlies the current Moho topography, and this is ultimately transferred to the nonuniform orogenic pattern found in northern Iberia.

Four decades of geophysical research on Iberia and adjacent margins

“…The presence of a highly reflective lower crust can explain the complex crustal models derived from both DSS and RFs and the disparity between the obtained results. Fernández-Viejo et al (2021) have recently proposed that the crustal roots beneath the Pyrenees and the Cantabrian Mountains are disconnected by the Basque Cantabrian Basin, that would not have experienced thickening due to its pre-convergence structure. The Moho map derived from surface wave does not reveal any crustal root beneath the Cantabrian Mountains, probably due to an insufficient data coverage beneath this zone (Palomeras et al, 2017).…”