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

Modelos analógicos de un cinturón no cilíndrico de pliegues y cabalgamientos alrededor de diapiros: resultados preliminares

Los modelos analógicos representan una herramienta muy útil para investigar el desarrollo progresivo de cinturones de pliegues y cabalgamientos. En este artículo, se presentan resultados preliminares de una serie de modelos realizados para estudiar el patrón estructural, alrededor de diapiros, de estructuras compresivas desarrolladas sobre un sustrato dúctil. Sobre los diapiros, simulados por cilindros de silicona, se generan pliegues y cabalgamientos. Esta debilidad mecánica produce también falta de cilindrism

Influencia de la geometría del indenter sobre el desarrollo de una cuña de pliegues y cabalgamientos arqueados: Resultados preliminares de modelos analógicos

Analogue models, with sand and silicone, have simulated the progressive development of an arcuate foldand- thrust belt around indenters of different geometry, which moved along a straight translation path. In the most external part of the model, the resulting geometry of the deformed wedge is roughly independent of the indenter form. Deformation affected only the frontal part of the indenter and the lateral deformation zone around the latter was very narro

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Analog Models of Fold-and-Thrust Wedges in Progressive Arcs: A Comparison With the Gibraltar Arc External Wedge

The timing and kinematics of the different types of structures and the associated vertical-axis rotations that permit an arcuate external wedge to acquire progressively its curved shape throughout its deformation history—known as progressive arcs—are key questions in natural cases of arcuate fold-and-thrust belts that we want to address through analog modeling. We present laboratory models of fold-and-thrust belts formed with a backstop that deforms in map view to simulate progressive arcs in a thin-skinned tectonic regime. Our setup makes use of a deformable backstop rigid enough to push from behind the initial parallelepiped but deformable in map view. This innovative design permits us to increase the amplitude of the arc indenting in the model as its radius of curvature decreases, that is, it simulates a progressive arc. Taking the Gibraltar Arc external wedge situated in the western Mediterranean to scale our models in terms of rheology, velocities, and sizes, four types of experiments were made. We varied the type of substratum (sand or silicone), the silicone thickness, and the width and length of the initial analog pack in order to test the influence of each of these parameters on the resulting fold-and-thrust belts. All experiments led to the formation of arcuate wedges where strain was partitioned into: (a) arc-perpendicular shortening, accommodated by thrusts which main structural trend is broadly subparallel to the indenter shape and with divergent transport directions, and (b) arc-parallel stretching, accommodated by normal and conjugate strike-slip faults. The normal and strike-slip faults contributed to the fold-and-thrust belt segmentation and the formation of independent blocks that rotated clockwise and counterclockwise depending on their position within the progressive arc. Our experiments allow to simulate and understand the finite deformation mode of the external wedge of the Gibraltar Arc. Accordingly, they shed light on how an arcuate fold-and-thrust belt can develop progressively in terms of structural trend and transport directions, types and distribution of the structures accommodating strain partition, and timing of vertical-axis rotations.This study was supported by projects RNM-0451, EST1/00231, CGL2017-89051-P, PGC2018-100914-B-I00, and UPO 1259543

Geoloday for a large audience: key points for its organization

Geoloday is an outreach initiative at national level, coordinated by the Geological Society of Spain. It consists in a fieldtrip guided by teams of geologists, with as much excursions as Spanish provinces. We analyze the participation in the last six editions. This bring us to determine the optimum format of this event when there is a lot of people, that is, the organizers fixed in the stops while the public moves by walking from one stop to the other. Finally, we give a series of key points in terms of organization to deserve a qualified attention to a lot of participants. At the same time, these advices are useful in order that not only these latter but also the organizers enjoy GeolodayGeolodía es una iniciativa de divulgación de la Geología de ámbito nacional, coordinada por la Sociedad Geológica de España. Consiste en excursiones de campo guiadas por equipos de profesionales de la geología, con tantas excursiones como provincias españolas. Analizamos la asistencia de las seis últimas ediciones que tuvieron lugar desde 2010 y determinamos el formato óptimo de esa jornada cuando el número de asistentes es muy alto: organizadores fijos en las paradas con el público andando entre ellas. Terminamos dando una serie de claves en cuanto a organización para que la atención sea de calidad y que tanto los asistentes como los organizadores disfruten de Geolodí