Lateral variations of pressure-temperature evolution in non-cylindrical orogens and 3-D subduction dynamics: the Betic-Rif Cordillera example

This paper is a contribution of the Orogen project funded by Total, BRGM and CNRS-INSU and it benefited from numerous discussions with the Orogen community. The 40Ar/39Ar facility at ISTO was funded and is supported by the ERC Advanced grant RHEOLITH, the LABEX project VOLTAIRE (ANR-10-LABX-100-01), the Région Centre project ARGON, and the project EQUIPEX PLANEX (ANR-11-EQPX-0036). We would to thank the guest-editor David Pedreira and the two reviewers, Juan Soto and André Michard for a really extensive analysis of our manuscript, which is obviously in better shape now. Special thanks are due to Federico Rossetti who commented on an early version of the manuscript.The long-term Pressure-Temperature-time-deformation (P-T-t-d) evolution of the internal zones of orogens results from complex interactions between the subducting lithosphere, the overriding plate and the intervening asthenosphere. 2-D numerical models successfully reproduce natural P-T-t-d paths, but most orogens are non-cylindrical and the situation is far more complex due to 3-D pre-orogenic inheritance and 3-D subduction dynamics. The Mediterranean orogens are intrinsically non-cylindrical. Their 3-D geometry results from the complex shape of the Eurasian and African margins before convergence and from the dynamics of slab retreat and tearing leading to strongly arcuate belts. More than many other segments, the Betic-Rif belt is archetypal of this behavior. A synthesis of the tectonometamorphic evolution of the Internal Zones, also based on recent findings by our group in the framework of the Orogen Project (Alboran domain, including the Alpujarride-Sebtide and Nevado-Filabride complexes) shows the relations in space and time between tectonic and P-T evolutions. The reinterpretation of the contact between peridotite massifs and Mesozoic sediments as an extensional detachment leads to a discussion of the geodynamic setting and timing of mantle exhumation. Based on new Ar-40/Ar-39 ages in the Alpujarride-Sebtide complex and a discussion of published ages in the Nevado-Filabride complex, we conclude that the age of the HP-LT metamorphism is Eocene in all complexes. A first-order observation is the contrast between the well-preserved Eocene HP-LT blueschists-facies rocks of the eastern Alpujarride-Sebtide Complex and the younger HT-LP conditions reaching partial melting recorded in the Western Alpujarride. We propose a model where the large longitudinal variations in the P-T evolution are mainly due to (i) differences in the timing of subduction and exhumation, (ii) the nature of the subducting lithosphere and (iii) a major change in subduction dynamics at similar to 20 Ma associated with a slab-tearing event. The clustering of radiometric ages obtained with different methods around 20 Ma results from a regional exhumation episode coeval with slab tearing, westward migration of the trench, back-arc extension and thrusting of the whole orogen onto the African and Iberian margins.TotalBRGMCentre National de la Recherche Scientifique (CNRS)ERC Advanced grant RHEOLITHLABEX project VOLTAIRE ANR-10-LABX-100-01Region Centre project ARGONproject EQUIPEX PLANEX ANR-11-EQPX-003

Overconsolidated flysch-type clays. Engineering considerations for the Strait of Gibraltar tunnel project

The stress-strain behaviour of 85 overconsolidated clay samples from Campo de Gibraltar Flysch Through Domain (Algeciras Unit, South Spain) is presented and discussed. The samples were identified and classified following ASTM standards while their chemical and mineralogical composition were determined by chemical and X-ray techniques. Several samples were tested under triaxial as well as oedometric conditions. Given the results, a detailed comparison was made between different theoretical constitutive models and real testing data, using the finite-elements method. The comparison indicated a good fit between experimental data and those found with finite-elements modelling when the Hardening Soil constitutive model was used. This model showed a better fit than did the Modified Cam -Clay model (historically used for modelling clayey soils), although the latter fit proved better for lower strain values (<5%) than higher ones. These results clarify this intermediate material (hard soils - weak rocks) behaviour and will help in Strait of Gibraltar tunnel project design, as these materials are widely involved in this tunnel design.Sergeyco Andalucía S.L.SECEGS

Método de la frecuencia de resonancia para la caracterización mecánica de rocas carbonáticas usadas como piedras de construcción

This work was supported by the Spanish Ministry of Universities via a doctoral grant to Fernando avi-la [FPU18/03607] . Special thanks to the Department of Mineralogy and Petrology of the University of Granada for the supply of the source materials and to Javier Roman Ramos, M.Sc. student, for his excellent work during the conduction of the tests.Nondestructive testing techniques have attracted growing interest in the last few years due to their ability to assess material properties without damaging the specimens. The free-free resonance method is a nondestructive testing technique based on the analysis of the natural frequencies of a sample. This study presents and discusses the applicability of this technique, traditionally used on soils, for the mechanical characterization of rocks. With this aim, the free-free resonance method is used to obtain the dynamic elastic modulus and shear modulus of four carbonate rocks that have been widely used as construction materials in southern Spain. The results from the nondestructive evaluation of dry and saturated rocks, in combination with petrographic characterization and uniaxial compression tests, make it possible to assess the existing relationships between the mechanical properties of carbonate rocks and to evaluate the impact of porosity and moisture content on their mechanical behavior.Las técnicas de ensayo no destructivo están atrayendo un creciente interés durante los últimos años debido a su capacidad para evaluar las propiedades sin dañar el espécimen. El Método de la Frecuencia de Resonancia es una técnica de ensayo no destructiva basada en el análisis de las frecuencias naturales de una muestra de material. Este estudio presenta y discute la aplicabilidad de esta técnica, tradicionalmente utilizada en suelos, para la caracterización mecánica de rocas. Con este objetivo, el Método de la Frecuencia de Resonancia es utilizado para obtener el módulo elástico dinámico y el módulo cortante dinámico de cuatro rocas carbonáticas ampliamente utilizadas como material de construcción en el sur de España. Los resultados de la evaluación no destructiva en rocas secas y saturadas, combinados con una caracterización petrográfica y ensayos de compresión uniaxial, permiten determinar las relaciones existentes entre las propiedades mecánicas de dichas rocas carbonáticas, así como evaluar el impacto de la porosidad y el contenido de humedad en su comportamiento mecánico.Spanish Government FPU18/0360

Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post-Subduction Delamination in the Western Mediterranean

Cenozoic extension in the Western Mediterranean has been related to the dynamics of back-arc domains. Although, in most of its orogenic belts extension propagated into the fore-arc nappe domains. Here we revisit the structure, metamorphism and radiometric ages of the Tunisian Tell, where HP/LT rocks (350°C at 0.8 GPa), were exhumed by the sequential activity of extensional detachments after heating and decompression (410°C–440°C at 0.6–0.3 GPa) in a plate convergent setting. Normal faults thinning the Tunisian Tell detached at two different crustal levels. The shallower one cuts down into the Atlas Mesozoic sequence, involving Tellian Triassic evaporites in the hanging-wall forming halokinetic structures in the Mejerda basin late Miocene. The deeper-detachment bounds metamorphic domes formed by marbles and metapsammites from the Atlas domain. Illite crystallinity on Triassic rocks shows epizonal to anchizonal values, at deep and intermediate structural depths of the Tell-Atlas nappe belt, respectively. New U-Pb 49.78 ± 1.28 Ma rutile ages from Tellian metabasites, together with existing phlogopite 23–17 Ma K-Ar ages in Atlas marbles from the footwall of the deepest detachment, indicate a polymetamorphic evolution. The Tell rocks underthrusted the Kabylian flysch in the early Eocene. Further, early Miocene shortening thrusted the metabasites over lower-grade sediments, producing HP/LT metamorphism and ductile stretching at the base of the Atlas belt. The exhumation of midcrustal roots of Western Mediterranean nappe belts after tectonic shortening is a common feature related to tearing at the edges of the subduction systems and inboard delamination of their subcontinental lithospheric mantle.Ministerio de Ciencia e innovación PID2019- 107138RB-I00P18-RT-3632 of the Junta de Andalucia,Erasmus Mundus External Cooperation Window and by Scientific Cooperation Agreement 0534 between the Office National des Mines (ONM)The Tunis el Manar University and the Group for Relief and Active Processes Analysis (ARPA) from the University of GranadaTunisian Company of Petroleum Activities (ETAP)Universidad de Granada / CBU

Preservation of the Iberian Tethys paleomargin beneath the eastern Betic mountain range

We are grateful to the staff involved in the TransCorBe project. The Geophysical Instrument Pool at GFZ-Potsdam provided most of the seismic equipment. We are grateful to Christian Haberland for his support. We want to thank two anonymous reviewers for the careful reading of the manuscript and the interesting and constructive criticism they provided. This work was funded by the Spanish State Research Agency (SRA) under the grant PID2019-109608GB I00/SRA/10.13039/501100011033, FEDER/MINECO project CGL2015-67130-C2-2-R, FEDER/Junta de Andalucia project A-RNM-421-UGR18 and research group RNM104 of the Junta de Andalucia. The Granada University/CBUA funding for open access charge.We obtain P-wave receiver functions from teleseismic earthquake recordings at a dense seismic broadband transect, deployed along 170 km across the Betic mountain range in southeastern Spain. Migrated images show the crustal structure of the orogen in detail. In particular, they reveal the situation of the subducted Iberian paleomargin, with full preservation of the proximal domain and the 50 km wide necking domain. Crustal thinning across the necking domain affects mainly the lower continental crust. The Variscan crust of the Tethys margin is bending downward beneath the Betics, reaching 45 km depth, and terminates abruptly at a major slab tear. The distal domain of the paleomargin cannot be reconstructed, but the migrated section suggests that material has been exhumed through the subduction channel and integrated into the Betic orogen. This supports an origin of the HP-LT Nevado-Filabride units from subducted, hyperextended Variscan crust. According to our profile, the present-day eastern Betics appear to have a much more significant contribution from metamorphic Iberian crust than previously thought.Geophysical Instrument Pool at GFZ-Potsdam - Spanish State Research Agency (SRA) PID2019-109608GB I00/SRA/10.13039/501100011033Spanish Government CGL2015-67130-C2-2-RFEDER/Junta de Andalucia project A-RNM-421-UGR18 RNM104Junta de Andaluci

Evidence for a developing plate boundary in the western Mediterranean

Acknowledgements The authors acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Complementary Action ESF TopoEurope TOPOMED (CGL2008- 03474-E/BTE) and national project EVENT (CGL2006-12861-C02-02). L.G.P. was funded by the Spanish Ministry of Education, Culture and Sport through the FPU fellowship AP2012-1579 and a Short-Term Scientific Mission (COST-STSM-ECOST-STSM-ES1301- 180814-045667) inside the COST Action ES1301. This study benefited from a Marie Skłodowska-Curie Individual Fellowship to L.G.P. (H2020-MSCA-IF-2017 796013), the project “MORPHOMED” (PID2019-107138RB-I00) funded by MCIN/SRA (State Research Agency/10.13039/501100011033), FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades/Projects (B-RNM-305-UGR18, A-RNM-508-UGR20 and P18-RT-3632), and acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) and C.R.R. project PID2019-109559RB-I00 of the Spanish “Ministerio de Ciencia e Innovación”.We thank the reviewers (JoaoDuarte and anonymous) for their insightful comments. This work has been carried out within Grup de Recerca Consolidat de la Generalitat de Catalunya “Barcelona Center for Subsurface Imaging” (2017 SGR 1662).Additional information Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41467-022-31895-z.The current diffuse-strain model of the collision between Africa and Eurasia in the western Mediterranean predicts a broad region with deformation distributed among numerous faults and moderate-magnitude seismicity. However, the model is untested because most deformation occurs underwater, at poorly characterized faults of undetermined slip. Here we assess the diffuse-strain model analysing two active offshore fault systems associated with the most prominent seafloor relief in the region. We use pre-stack depth migrated seismic images to estimate, for the first time, the total Plio-Holocene slip of the right-lateral Yusuf and reverse Alboran Ridge structurally linked fault system. We show that kinematic restoration of deformational structures predicts a slip of 16 ± 4.7 km for the Alboran Ridge Fault and a minimum of 12 km for the Yusuf Fault. Thus, this fault system forms a well-defined narrow plate boundary that has absorbed most of the 24 ± 5 km Plio-Holocene Africa-Eurasia convergence and represents an underappreciated hazard.MCIN Projects A-RNM-508-UGR20, B-RNM-305-UGR18, P18-RT-3632H2020 Marie Skłodowska-Curie Actions H2020-MSCA-IF-2017 796013, PID2019-107138RB-I00Society for Research on AdolescenceGeneralitat de Catalunya 2017 SGR 1662Ministerio de Educación, Cultura y Deporte AP2012-1579, COST-STSM-ECOST-STSM-ES1301-180814-045667, ES1301 MECDMinisterio de Economía y CompetitividadMinisterio de Ciencia e InnovaciónSevero Ochoa Centre of Excellence CEX2019-000928-S, PID2019-109559RB-I0

The restoration of San Pedro cliff at La Alhambra: calculation aspects

La muralla-palacio de La Alhambra, que es Patrimonio de la Humanidad, se ve amenazada por el avance del Tajo de San Pedro (Figura1), un diedro de 65,5 m de altura, que corta la colina de La Alhambra y que se ha situado a sólo 23,8 m de ella. Existe en la zona un régimen tectónico de extensión que afloja el terreno y activa la caída de lajas. Otra causa importante del deterioro del Tajo es la erosión. El coeficiente de seguridad al deslizamiento del Tajo sometido al terremoto de periodo de retorno de 1.000 años es de 0,73. La solución propuesta para su preservación es una malla de alambre postesada de alto límite elástico y revegetación autóctona. La presión que puede llegar a aplicar la malla en servicio eleva el coeficiente de seguridad con sismo a un valor próximo a uno. Mediante una simulación en ordenador se ha analizado el impacto ambiental.San Pedro cliff (Figure 1) is a dihedral 65.5 m high, which has progressed to place itself at 23.8 m from the Alhambra wall-palace that is a heritage of the Humankind. Active normal faults surrounding the cliff have created an extension tectonic regime that loosens the ground and activates the slab falls. One of the faces of the dihedral is a major fault. The cliff’s factor of safety subject to the 1000 years return period earthquake is 0.73. The preservation solution proposed is a post-tensioned high elastic limit wire mesh and autochthonous vegetation. With this reinforcement, the factor of safety under that earthquake raises to a value around one. A computer simulation has permitted to analyse the environmental impact.Este trabajo se ha realizado con ayuda del proyecto de investigación BIA 2004-01302 del Ministerio de Educación y Ciencia

Improving landslide inventories by combining satellite interferometry and landscape analysis: the case of Sierra Nevada (Southern Spain)

An updated and complete landslide inventory is the starting point for an appropriate hazard assessment. This paper presents an improvement for landslide mapping by integrating data from two well-consolidated techniques: Differential Synthetic Aperture Radar (DInSAR) and Landscape Analysis through the normalised channel steepness index (ksn). The southwestern sector of the Sierra Nevada mountain range (Southern Spain) was selected as the case study. We first propose the double normalised steepness (ksnn) index, derived from the ksn index, to remove the active tectonics signal. The obtained ksnn anomalies (or knickzones) along rivers and the unstable ground areas from the DInSAR analysis rapidly highlighted the slopes of interest. Thus, we provided a new inventory of 28 landslides that implies an increase in the area affected by landslides compared with the previous mapping: 33.5% in the present study vs. 14.5% in the Spanish Land Movements Database. The two main typologies of identified landslides are Deep-Seated Gravitational Slope Deformations (DGSDs) and rockslides, with the prevalence of large DGSDs in Sierra Nevada being first revealed in this work. We also demonstrate that the combination of DInSAR and Landscape Analysis could overcome the limitations of each method for landslide detection. They also supported us in dealing with difficulties in recognising this type of landslides due to their poorly defined boundaries, a homogeneous lithology and the imprint of glacial and periglacial processes. Finally, a preliminary hazard perspective of these landslides was outlined.Universidad de Granada/CBUAMarie Curie Actions B-RNM-305-UGR18 A-RNM-508-UGR20 P18-RT-3632ERDF through the project RISKCOAST' of the Interreg SUDOE Programme SOE3/P4/E0868Project MORPHOMED' from the Spanish Ministry of Science (MCIN)/State Research Agency (SRA) PID2019-107138RB-I00Ramon y Cajal' Programme of the Spanish Ministry of Science RYC-2017-23335NoR 6373

The restoration of San Pedro cliff at La Alhambra. Calculation aspects

RESUMEN. La muralla-palacio de La Alhambra, que es Patrimonio de la Humanidad, se ve amenazada por el avance del Tajo de San Pedro (Figura1), un diedro de 65,5 m de altura, que corta la colina de La Alhambra y que se ha situado a sólo 23,8 m de ella. Existe en la zona un régimen tectónico de extensión que afloja el terreno y activa la caída de lajas. Otra causa importante del deterioro del Tajo es la erosión. El coeficiente de seguridad al deslizamiento del Tajo sometido al terremoto de periodo de retorno de 1.000 años es de 0,73. La solución propuesta para su preservación es una malla de alambre postesada de alto límite elástico y revegetación autóctona. La presión que puede llegar a aplicar la malla en servicio eleva el coeficiente de seguridad con sismo a un valor próximo a uno. Mediante una simulación en ordenador se ha analizado el impacto ambiental.ABSTRACT. San Pedro cliff (Figure 1) is a dihedral 65.5 m high, which has progressed to place itself at 23.8 m from the Alhambra wall-palace that is a heritage of the Humankind. Active normal faults surrounding the cliff have created an extension tectonic regime that loosens the ground and activates the slab falls. One of the faces of the dihedral is a major fault. The cliff’s factor of safety subject to the 1000 years return period earthquake is 0.73. The preservation solution proposed is a posttensioned high elastic limit wire mesh and autochthonous vegetation. With this reinforcement, the factor of safety under that earthquake raises to a value around one. A computer simulation has permitted to analyse the environmental impact

Evaluation of the SBAS InSAR Service of the European Space Agency’s Geohazard Exploitation Platform (GEP)

The analysis of remote sensing data to assess geohazards is being improved by web-based platforms and collaborative projects, such as the Geohazard Exploitation Platform (GEP) of the European Space Agency (ESA). This paper presents the evaluation of a surface velocity map that is generated by this platform. The map was produced through an unsupervised Multi-temporal InSAR (MTI) analysis applying the Parallel-SBAS (P-SBAS) algorithm to 25 ENVISAT satellite images from the South of Spain that were acquired between 2003 and 2008. This analysis was carried out using a service implemented in the GEP called “SBAS InSAR”. Thanks to the map that was generated by the SBAS InSAR service, we identified processes not documented so far; provided new monitoring data in places affected by known ground instabilities; defined the area affected by these instabilities; and, studied a case where GEP could have been able to help in the forecast of a slope movement reactivation. This amply demonstrates the reliability and usefulness of the GEP, and shows how web-based platforms may enhance the capacity to identify, monitor, and assess hazards that are associated to geological processes.Spanish “Juan de la Cierva” grants support part of the work of Jorge P. Galve. The expenses related to the hired researcher contract of Jorge P. Galve and the field surveying were funded by the project CGL2015-67130-C2-1-R (FEDER and Spanish Ministry of Economy and Competitiveness)