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The Iberian Central System represents an outstanding topographic feature in the central Iberian Peninsula. It is an intraplate mountain range formed by igneous and metasedimentary rocks of the Variscan Iberian Massif that has been exhumed since the Eocene in the context of the Alpine orogeny. The Iberian Central System has been conventionally interpreted as a thick-skinned pop-up mountain range thrust over the Duero and Tajo foreland basins. However, its lithospheric structure and the P-wave velocity distribution are not yet fully resolved. In order to place geophysical constraints on this relevant topographic feature, to identify lithospheric discontinuities, and to unravel the crustal deformation mechanisms, a wide-angle seismic reflection and refraction experiment, CIMDEF (Central Iberian Mechanism of DEFormation), was acquired in 2017 and 2019. It is a NNW-SSE oriented 360-km long profile that runs through the Duero basin, the Iberian Central System and the Tajo basin. First results based on forward modeling by raytracing show an irregularly layered lithosphere and allow to infer the depth extent of the northern Iberian Central System batholith. The crust is ~ 31 km thick under the Duero and Tajo basins and thickens to ~ 39 km under the Iberian Central System. A conspicuous thinning of the lower crust towards the south of the Iberian Central System is also modeled. Along this transect, a continuous and high amplitude upper mantle feature is observed and modeled as the reflection of an interface dipping from 58 to 62 km depth featuring a P-wave velocity contrast of 8.2 to 8.3 km/s. Our preliminary results complement previous models based on global-phase seismic and noise interferometry and gravity data, provide new constraints to validate the accuracy of passive seismic methods at lithospheric scale, and contribute with a resolute P-wave velocity model of the study area to unravel the effect of the Alpine reactivation on the central Iberian Massif.This project has been funded by the EIT-RawMaterials 17024 (SIT4ME) and the MINECO projects: CGL2016-81964-REDE, CGL2014-56548-P.

The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: the Duero Basin to the north, located at 750-800m, and the Tajo Basin to the south, lying at 450-500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data are able to constrain the geometry of this crustal root, which appears to be defined by a northward lower-crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. In addition, the lower crust might have thinned, allowing coupled deformation at both crustal levels. This implies that the reactivated upper-crustal fractures can reach lower-crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constraints on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. The results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF (Central Iberian Massif DEFormation Mechanisms) profile. Although the resolution of the dataset features limited resolution (0.5-4 Hz, stations placed at similar to 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny., This research has been supported by the Ministerio de Ciencia e Innovacion (grant nos. CGL2014-56548-P and CGL2016-81964-REDE), the Consejeria de Educacion, Junta de Castilla y Leon (grant no. SA065P17), and the Generalitat de Catalunya (grant no. 2017-SGR-1022).

EGU2020: Sharing Geoscience Online, 4-8 may 2020, Sub-Moho reflectors have been identified in seismic refraction and wide-angle reflection recordings in western Iberia since the late `80s. These control source seismic wide-angle shot records have energy large enough to illuminate the uppermost mantle showing strong sub-Moho arrivals at distant offsets (>180 km) with amplitudes significantly higher than the Pn and a relatively long coda. The kinematics and wavelet characteristics of these features are probably produced by an increase in P-wave velocity, and forward modeling indicates that these arrivals reflect off an interface in the 60-80 km depth range beneath the Iberian Massif. The waveform and time length of this arrival suggests that it can result from the interaction of the seismic energy with a ~10 km thick heterogeneous layer. To test this hypothesis, we used a 2D second-order finite-difference acoustic and elastic full wave-field scheme with a layer consisting of randomly distributed bodies smaller than ¿ of the wavelength of the seismic waves in thickness and ¿Vp=±0.2 km/s at the considered depth range. Resulting synthetic shot gathers reproduce well the observed amplitudes and codas as a result of the constructive interference caused by the tuning effect produced by this gradient heterogeneous zone. The contrast in physical properties and depth level of this feature are consistent with the top of the phase transition from spinel to garnet lherzolite, the so-called Hales discontinuity. Some of the available gathers show a second and deeper reflection. Detailed analysis of the reflected wave-forms suggests that the reflected wavelet has reversed polarity, a feature suggesting. a velocity decrease with depth. Finite difference acoustic and elastic full wave-field modeling places this discontinuity around 90 km depth beneath the Ossa-Morena Zone (south Iberian Massif). A lateral change is observed beneath the Centro-Iberian Zone (central Iberian Massif) where it is imaged at 103-110 km depth on the southeast and shallows up to 80 km depth on the northeast. The indicated depth would be consistent with the depth location of the LAB, which is relatively well constrained for the target area by other geophysical observations., Funding resources: EU EIT-RawMaterials Ref: 17024_20170331_92304; MINECO: CGL2016-81964-REDE CGL2014-56548-P: JCYL: SA065P17).

[ES] El Sistema Central Ibérico es una cordillera intraplaca ubicada en la Zona Centro Ibérica. Divide la meseta Ibérica en dos sectores: la Cuenca del Duero al N y la Cuenca del Tajo al S. La topografía de la zona es muy variable, teniendo la Cuenca del Tajo una altitud media en torno a 400 m mientras que la Cuenca del Duero presenta una elevación media más alta, de 750-800 m. El Sistema Central Ibérico se caracteriza por una configuración estructural en “pop-up” y “pop-dow” formada por una tectónica tipo “thick skinned” como consecuencia de la reactivación de estructuras Variscas durante la orogenia Alpina. La alta topografía es probablemente el reflejo de una corteza tectónicamente engrosada que también debería ser identificada por, i) la geometría de la discontinuidad corteza- manto, ii) una configuración cortical que exhiba estructuras imbricadas, y/o iii) como un resultado de las características reológicas de la litosfera. El principal objetivo de esta investigación es poder discriminar y entender cada una de estas contribuciones. En este trabajo se presenta un modelo a escala litosférica de esta parte del Macizo Ibérico. Para ello, se han utilizado los datos del proyecto CIMDEF, que consiste en la adquisición de ruido sísmico ambiental y de terremotos distantes durante 1–2 meses, a lo largo de un perfil casi lineal. Estos datos sísmicos se han registrado en 69 estaciones de corto período dispuestas a lo largo de una transecta de ≃ 320 km de longitud. La interpretación de los datos se ha realizado mediante la aplicación de diferentes técnicas de Interferometría Sísmica, lo que nos ha permitido lograr imágenes, más o menos detalladas, de la estructura bajo la cordillera. La aplicación de esta técnica supone una aproximación al proceso por el cual se genera la reflectividad bajo una estación sísmica, simulando las características por las que se registra energía sísmica procedente del interior de la Tierra cuando esta incide de forma (casi) vertical. Los resultados revelan, tal y como se esperaba, un claro engrosamiento de la corteza bajo el Sistema Central Ibérico. Este es la consecuencia de una imbricación cortical que afecta a la parte inferior de la misma y probablemente a la superior. Esto implica que la geometría de la cordillera es asimétrica, similar a la de otras cadenas alpinas (por ejemplo, los Pirineos) y que, a diferencia de los modelos propuestos anteriormente, la deformación por buckling o flexura ha jugado un papel menor en la configuración de la misma. Además, la evolución tardi-Varisca del NO de Iberia, caracterizada por un colapso gravitacional, extensión y fusión cortical, ha condicionado la estructura cortical de la Zona Centro Ibérica, afectando a la posterior evolución de la misma y, por ello, a sus características actuales. Por un lado, la corteza está altamente removilizada y es más delgada en esta área, como lo demuestra el cálculo de la profundidad a la que se encuentra el Punto de Curie, presentado como parte de esta tesis. Además, la discontinuidad que separa la corteza superior de la inferior y que se identifica a lo largo de todo el Macizo Ibérico ha sido, probablemente, asimilada por los granitoides que se encuentran bajo el Sistema Ibérico Central. Esto permite que los cabalgamientos y fallas superficiales puedan continuar en profundidad, cortando toda la corteza y conectando con la imbricación observada en la corteza viii inferior. Este hecho permitiría que la corteza superior subduzca ligeramente de manera conjunta con la corteza inferior y se hunda bajo el Sistema Central Ibérico. Este proceso es, muy probablemente, responsable del contraste de altitud que se observa entre las mesetas al N y S del Sistema Central Ibérico. Finalmente, el manto en la Zona Centro Ibérica no es magnético, ya que es más profundo que la isoterma 580◦ C. Sin embargo, muestra una reflectividad escasa que se relaciona, tentativamente, con la discontinuidad de Hales ya identificada hacia S del perfil CIMDEF.

A multidisciplinary study has been carried out in Hontomín (Spain) to determine the basement structural setting, its geometry and the geometry of the sedimentary succession of an area aimed to be the first Spanish pilot plant for CO2 storage. An integration of coincident 3-D seismic results, borehole data and unpublished microgravity data were used to reproduce the deep structure and topography of the basement and to quantify the thickness of the Triassic Keuper evaporites. The subsurface structure is characterized by a half-graben setting filled with Keuper evaporites (up to 2000m thick), forming an extensional forced fold. All data sets clearly identify two main fault systems, compartmentalizing the main structural domain into three differentiated blocks. These faults have been interpreted to be reactivated normal faults that have led to the formation of the Hontomín dome.

Publicado en la revista como Special Issue:Abstracts of the International Symposium on Deep Earth Exploration and Practices, 24–26 Oct 2018, Beijing, China, The Iberian Peninsula and its margins have been extensively studied by multi-seismic data acquisition experiments since the early 70’s. Relatively old seismic refraction (form the 70’s to the late 80’s) and more modern (early 90’s to present day) spatially dense wide-angle seismic reflection transects have constrained the distribution of P and S wave velocity and the depth and geometry of the main crustal and lithospheric interfaces. Deep normal incidence high resolution seismic reflection surveys imaged: the crustal architecture; the distribution of deformation and help determine the evolution of the most relevant geologic features within Iberia and its margins. Deep seismic imaging started with the Spanish-French collaboration across the Pyrenees (ECORS-Pyrenees), and it was soon after followed by the ESCI program in the mid-80’s. Similar to other Deep Continental Seismic Reflection Programs (ECORS, DEKORP, BIRPS in EU and LITHOPROBE, COCORP in Canada and USA), ESCI acquired a series of on-land and marine seismic transects that revealed the internal architecture of key orogenic belts within Iberia, namely the Betic Cordillera and the northern part of the Iberian Massif (Iberian part of the European Variscan orogen). Later, the EUROPROBE initiative fostered detailed studies of the central and southern part of the Iberian Massif. Two 300 km long transects (IBERSEIS and ALCUDIA) imaged this orogen in SW Iberia. The resulting seismic profiles sampled three major tectonic blocks which collided in the late Paleozoic: form south to north these are: the South Portuguese, the Ossa-Morena and, the Central Iberian blocks. These terranes and their sutures show characteristic seismic fabrics. These seismic signatures reveal a distribution of the deformation that gives valuable insights into the evolution of the orogen, e.g. thickening and thinning mechanisms, igenous activity and strike slip tectonics. The upper and lower crusts appear to be decoupled along an interface that runs through the entire seismic transects. Deformation seems to have been accommodated in different ways at upper and crustal levels in the three tectonic blocks. Furthermore, the northern part of the southernmost transect (the IBERSEIS transect) images a 1-2 s thick high amplitude reflective sill-like structure located at mid crustal levels. It has been interpreted as a mafic sill intrusion along a mid-crustal decollement. The Central Iberian Zone, imaged by the ALCUDIA transect, reveals thick and highly reflective lower crust, the reflection fabric consists of relatively continuous, sub-horizontal to arcuate events, suggesting that deformation is mostly associated with ductile deformation. The Moho features a laterally variable seismic signature (highly reflective beneath the Central Iberian Zone, discontinuous and diffuse below the Ossa-Morena Zone and, sharp and well defined to the south of the South Portuguese Zone). Along the entire transect, the Moho is subhorizontal and located at an average depth of 31-35., Research supports: CGL2014-56548-P, CGL2016-81964-REDE; SIT4ME EIT-KIC-RawMaterials; 2017-SGR-1022