Thermal and mechanical structure of the central Iberian Peninsula lithosphere

Abstract

The central Iberian Peninsula (Spain) is made up of three main tectonic units: a mountain range, the Spanish Central System and two Tertiary basins (those of the rivers Duero and Tajo). These units are the result of widespread foreland deformation of the Iberian plate interior in response to Alpine convergence of European and African plates. The present study was designed to investigate thermal structure and rheological stratification in this region of central Spain. Surface heat flow has been described to range from f 80 to f 60 mW m À2 . Highest surface heat flow values correspond to the Central System and northern part of the Tajo Basin. The relationship between elevation and thermal state was used to construct a one-dimensional thermal model. Mantle heat flow drops from 34 mW m À2 (Duero Basin) to 27 mW m À2 (Tajo Basin), and increases with diminishing surface heat flow. Strength predictions made by extrapolating experimental data indicate varying rheological stratification throughout the area. In general, in compression, ductile fields predominate in the middle and lower crusts and lithospheric mantle. Brittle behaviour is restricted to the first f 8 km of the upper crust and to a thin layer at the top of the middle crust. In tension, brittle layers are slightly more extended, while the lower crust and lithospheric mantle remain ductile in the case of a wet peridotite composition. Discontinuities in brittle and ductile layer thickness determine lateral rheological anisotropy. Tectonic units roughly correspond to rheological domains. Brittle layers reach their maximum thickness beneath the Duero Basin and are of least thickness under the Tajo Basin, especially its northern area. Estimated total lithospheric strength shows a range from 2.5Â10 12 to 8Â10 12 N m À1 in compression, and from 1.3Â10 12 to 1.6Â10 12 N m À1 in tension. Highest values were estimated for the Duero Basin. Depth versus frequency of earthquakes correlates well with strength predictions. Earthquake foci concentrate mainly in the upper crust, showing a peak close to maximum strength depth. Most earthquakes occur in the southern margin of the Central System and southeast Tajo Basin. Seismicity is related to major faults, some bounding rheological domains. The Duero Basin is a relative quiescence zone characterised by higher total lithospheric strength than the remaining units. D

Recent tectonic model for the Upper Tagus Basin (central Spain)

“…This zone is related with instrumental seismicity of magnitude maximum as M4.2 (Escopete earthquake, 7 th June of 2007), shallow normal earthquakes (depth < 10 km) and located between the area bounded by the Tagus River and the Jarama River. This basement flexure is in agreement with the regional stress/strain tensor defined in this area by others authors De Vicente et al, 1996;Herraiz et al, 2000;Tejero and Ruiz, 2002;De Vicente et al, 2007Fernández-Lozano et al, 2011). Reverse earthquakes are deeper than normal earthquakes (16 km > depth > 10 km) in agreement with the geometry of the flexure and the strain field defined upper and down of the non deformation surface (strain deformation distribution in flexural folding with extrados/stretching and intrados/shortening).…”

“…Reverse earthquakes are deeper than normal earthquakes (16 km > depth > 10 km) in agreement with the geometry of the flexure and the strain field defined upper and down of the non deformation surface (strain deformation distribution in flexural folding with extrados/stretching and intrados/shortening). The interval of depth is according to the lower limit for the upper crust defined by Tejero and Ruiz (2002). However, new thermal models are required for describe the compressive and extensional distribution of the lithosphere within the Tagus Basin.…”

“…Thermal and rheological models for the SCS and adjacent areas were developed by Suriñach and Vegas (1988) and Tejero and Ruiz (2002), with a surface heat flow ranging between 80 and 60 mWm -2 , and with the Moho located at 31-34 km in depth. Jiménez-Díaz et al (2012) suggested a value ranging between 81-83 mWm -2 of the surface heat flow for the Tagus Basin, involving mantle processed to the continuous uplift of the SCS.…”

“…Pérez-López et al (2005) described the stress-field at the South Border of the SCS as strike-slip to uniaxial extension from Eocene to present. Martín-Velázquez et al (2009) modeled this stress-field by using finite elements and a punctual rheological model obeying the thermal model of Tejero and Ruiz (2002). The relevance of this model is the simulation of the stress state at the surface of the SCS, where the present topography plays as tectonic loading for faults.…”

Petrogenesis of Permian alkaline lamprophyres and diabases from the Spanish Central System and their geodynamic context within western Europe

“…The present lithospheric thickness in central Spain is arOlll1 d 110 km (Fernandez et a1. 1998;Tejero and Ruiz 2002) and the region seems to have been tectonic ally stable since Permian times. Moreover, alkaline melt generation occur red at great depth (the stability field of garnet in peridotites ranges down to around 80 km; Nickel 1986) close to the proposed lithosphere-asthenosphere boundary.…”