Insights into the "tectonic topography" of the present-day landscape of the central Iberian Peninsula (Spain)

The landscape of today’s central Iberian Peninsula has been shaped by ongoing tectonic activity since the Tertiary. This landscape comprises a mountain ridge trending E–W to NW–SE, the Central System, separating two regions of smooth topography: the basins of the rivers Duero and Tajo. In this study, we explore interrelationships between topography and tectonics in the central Iberian Peninsula. Regional landscape features were analysed using a digital elevation model (DEM). Slope gradients and slope orientations derived from the DEM were combined to describe topographic surface roughness. Topography trendsurfaces inferred from harmonic analysis were used to define regional topographic features. Low roughness emphasizes the smooth nature of the basins’ topography, where surfaces of homogeneous slope gradient and orientation dominate. High roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests, valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins. One of the applications of roughness mapping was its capacity to isolate incised valley segments. The area distribution of incised rivers shows their prevalence in the east. On a regional scale, the topographic surface can be described as a train of NE–SW undulations or waves of 20 km wavelength. These undulations undergo changes in direction and interruptions limited by N–S-trending breaks. E–W and NE–SW troughs and ridges clearly mark structural uplifts and depressions within the Central System. These structures are transverse to the compressive NW–SE stress field that controlled the deformation of the central Iberian Peninsula from the Neogene to the present. They represent the upper crustal folding that accommodates Alpine shortening. N–S breaks coincide with Late Miocene faults that control the basins’ sedimentation. Further, associated palaeoseismic structures suggest the recent tectonic activity of N–S faults in the eastern part of the Tajo Basin. Apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 Ma which induced the river incisions appearing in the roughness map. N–S and NE–SW faults could be seismogenic sources for the current moderate to low seismic activity of the east Tajo Basin and southeast Central System. Although N–S fault activity has already been established, we propose its significant contribution to shaping the landscape

Estimating the effective elastic thickness of the lithosphere of the Iberian peninsula based on multitaper spectral analysis

Effective elastic thickness of the lithosphere of the Iberian peninsula was estimated from a coherence analysis of topography and gravity spectra, for which a multitaper technique was used. Coherence estimates provide an average Te value of 17 ± 4 km. To verify the Te derived from the spectral analysis, we compare it to independent Te estimates from strength envelopes constructed for some tectonic units located at the interior of the Iberian peninsula.We obtain Te values ranging from 10 to 25 km. These values are consistent with coherence results. Tectonic evolution of the area involved an Early Mesozoic rifting (Late Permian—Early Cretaceous) and a subsequent period of compression. Present morphotectonic units result from Alpine deformation events (mainly Neogene). No widespread volcanism activity or/and high heat flow values have been reported to have occurred during intraplate domain deformation. The Iberian lithosphere response to loading primarily reflects its pre-existing inherited mechanical structure, which has remained thermally relatively unperturbed