Crustal Imbrication in an Alpine Intraplate Mountain Range: A Wide‐Angle Cross‐Section Across the Spanish‐Portuguese Central System

Abstract

Intraplate ranges are topographic features that can occur far from plate boundaries, the expected position of orogens as described in the plate tectonics theory. To understand the lithospheric structure of intraplate ranges, we focused on the Spanish‐Portuguese Central System (SPCS), the most outstanding topographic feature in the central Iberian Peninsula. The SPCS is an Alpine range that exhumes Precambrian‐Paleozoic rocks and is located at >200 km from the northern border of the Iberian microplate. Here, we provide a P‐wave velocity model based on wide‐angle seismic reflection/refraction data of the central SPCS (Gredos sector). Our results show: (a) a layered lithosphere characterized by three major interfaces: Conrad, Mohorovicic, and Hales discontinuities, (b) an asymmetry of the crust‐mantle boundary under the SPCS, (c) the extent of the Variscan batholith forming the main outcrops of Gredos, and (d) the thinning of the lower crust toward the south. This model suggests that the exhumation of the SPCS basement was driven by a south‐vergent thick‐skinned thrust system, developed in the southern part of the SPCS and that promoted crustal imbrication and a Mohorovicic discontinuity's offset under the SPCS. Thus, the deformation mechanisms of the crust seem to be controlled by the presence of the late‐ to post‐Variscan granitoids that assimilated the Variscan mid‐crustal detachment creating a new rheological boundary. This tectonic structure allowed the formation of Alpine crustal‐scale thrust systems that eased coupled deformation of the upper and lower crust, leading to limited underthrusting of both crustal layers.

Mega‐Folding of a Basement During Incipient Intra‐Plate Continental Subduction (Alpine Central Iberia)

“…Recent seismic studies indicate that the SCS passes through the entire crust and cuts off the Moho (Andrés et al., 2019, 2020; DeFelipe et al., 2022). The studied seismic section is located to the west of the Hiendelaencina Dome, but the SCS crops out up to the Madrid meridian.…”

“…The resulting structure in the upper plate would be an asymmetric antiform verging toward the lower plate, that is, to the SE (Figure 6b). This is essentially the large‐scale Alpine structure of the study area, and, in a broad sense, accounts for the topographic upwarping of the hanging wall to the SCS along the SPCS (DeFelipe et al., 2022).…”

Identification of natural and anthropogenic signals in controlled source seismic experiments

“…Figure 1 shows a record section of this shot, clearly displaying P and S waves all along the profile. A first ray-tracing model of this shot is included in 13 . The reader is referred to this paper to get the details of its tectonic interpretation.…”

“…The analysis of seismic waves generated by this source can provide relevant information, as the acquisition of seismic profiles with fan geometry has proved to be useful to detect lateral variations in the crustal structure 31,32 . Modeling of this fan profile can provide additional constraints to the crustal structure deduced from forward 2D ray-tracing modeling along the CIMDEF line 13 .…”