Crustal structure of the Iberian Central System (Iberian Peninsula: The wide-angle seismic reflection CIMDEF experiment

Abstract:

One of the most complete sections of the Variscan orogen outcrops in the western part of the Iberian Peninsula. Since the early 90s it has been the target of a number of geophysical studies to characterize its lithospheric structure. The internal architecture of the Iberian microplate presents critical constraints on the way the Iberian crustal lithosphere responds to the imposed stress regime. This is a compressive tectonic environment result of the collision between European and African continents. This stress regime is most probably responsible for the deformation patterns that are reflected by the Topographic relief of the Iberian Peninsula with a few intraplate orogens. The central Iberian system constitutes a major intraplate orogenic belt conventionally interpreted as a pop up structure. In order to place geophysical constraints on this relevant topographic feature, crustal structure and deformation style a wide-angle seismic reflection and refraction experiment, CIMDEF (Central Iberian Mechanism of DEFormation), was acquired in 2017 and 2019. It consisted of three NNW-SSE and E-W oriented profiles ranging between 130 and 330 km in length. These profiles run through the Duero basin, the Spanish Central System and the Tajo basin, allowing us to construct a P-wave velocity model in this sector of the Central Iberian Zone. First results based on forward modeling by raytracing show a crust of ~ 32 km thick under the Duero and Tajo basins that thickens to ~ 40 km under the Spanish Central System. A reduction of the lower crust thickness towards the south of the Spanish Central System is also modeled. At far offsets (> 190 km), an upper mantle reflection is observed, modeled as an interface at 60 to 68 km depth with a P-wave velocity contrast of 8.3 to 8.4 km/s. Our preliminary results complement previous models in this area based on Global-Phase Seismic Interferometry and gravity data; provide new constraints to validate the accuracy of passive seismic methods at lithospheric scale in the Variscan orogeny; and contribute with a resolute model of the P-wave velocity in the study area.

This project has been funded by the EIT-RawMaterials 17024_20170331_92304; and MINECO: CGL2016-81964-REDE, CGL2014-56548-P.