Strain partitioning in the eastern-end of the Torcal Shear Zone (Betics, S Spain)

The eastern end of the Torcal Shear Zone (TSZ) is made up of two structural domains that accommodate variable proportions of the strain partitioning associated to the TSZ dextral transpressive deformation. The Sierra de las Cabras Domain is a dextral transpressive band at an angle to the TSZ giving way southeastward to the Sierra de Camorolos Domain, whose thrusts and folds accommodate mainly coaxial strain, though some dextral component must be present. Kinematic analysis carried out on these structures permit to establish a range between N120º-160ºE for the far-field displacement vector in this sector, in contrast to the WNW-ESE orientation obtained for the central TSZ. Given that the structural organization is coeval in the whole ZCT, the difference in the far-field displacement vector orientation may point to a decreasing simple shear component toward the end of the dextral transpressive bandLa terminación oriental de la Zona de Cizalla del Torcal (ZCT) está definida por dos dominios estructurales que acomodan el reparto de la deformación transpresiva dextra de la ZCT en proporciones variables. El Dominio de la Sierra de las Cabras es una banda transpresiva dextra, oblicua a la ZCT, que se releva en su sector SE con el Dominio de Sierra de Camorolos, cuyos cabalgamientos y pliegues acomodan una deformación principalmente coaxial, aunque con cierta componente dextra. El análisis cinemático de estas estructuras permite estimar un vector de desplazamiento con una orientación comprendida entre N120º-N160ºE, frente a la orientación ONO-ESE obtenida de los macizos centrales de la ZCT. Dado que la organización estructural de los dos dominios es coetánea con la que registra el resto de la ZCT, podría concluirse que la diferencia en la orientación de los vectores de desplazamiento responde a una disminución de la componente de cizalla simple de la deformación transpresiva dextra hacia la zona de terminación de la band

Orientación preferente de forma de cuerpos de dolomías de una broken formation triásica en las Béticas Externas occidentales

Detailed structural analyses of block-in-matrix formations are key to understand the tectonic processes involved in the external zones of many convergent orogens. One of these formations, with a highly controversial origin and evolution, marks the boundary between the fold-and-thrust belt and the foreland basin of the Betics. We analyzed dolostone bodies from this block-in-matrix formation in the western External Betics (Badolatosa, Sevilla), affected by the Algodonales-Badolatosa shear zone, to obtain a partial SPO (θ angle between long axes and the shear zone boundary). Our results define a main 500-1200 m-wide band strongly controlled by deformation at the WNW-NNW boundary of this shear zone. Minor, heterogeneously distributed bands with a moderate SPO are tentatively interpreted as Riedel shears related to dextral transpressionEl análisis estructural detallado de formaciones con fábricas de tipo block-in-matrix es clave para entender los procesos tectónicos que ocurren en las zonas externas de numerosos orógenos convergentes. Una de estas formaciones, con origen y evolución muy controvertidos, marca el límite entre el cinturón de pliegues y cabalgamientos y la cuenca de antepaís de las Béticas. Hemos analizado los cuerpos de dolomías de esta formación de tipo block-in-matrix de las Béticas occidentales (Badolatosa, Sevilla), afectada por la zona de cizalla de Algodonales-Badolatosa, para obtener una SPO parcial (ángulo θ entre los ejes largos y el límite de la zona de cizalla). Nuestros resultados muestran una banda de 500-1200 m de ancho fuertemente controlada por la deformación en el límite ONO-NNO de dicha zona de cizalla. Bandas con una SPO moderada, distribuidas heterogéneamente, podrían interpretarse como cizallas Riedel relacionadas con una transpresión dextr

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

Patrones complejos de reparto de la deformación evaluados mediante modelos de transpresión triclínica. Análisis cinemático preliminar del macizo del Valle de Abdalajís (zona de cizalla del Torcal, zonas externas Béticas)

Complex strain partitioning patterns are very common in the continental crust. They are often related to the kinematics of three-dimensional deformations and hence, can be analysed using transpression models. In this work, the strain partitioning pattern of the Valle de Abdalajís massif is evaluated with a model of triclinic transpression with oblique extrusion. Structures and kinematics are compared with the output of the model.We present preliminary results suggesting that the far-field vector responsible for bulk deformation at the studied area would be oriented NO75ºE-N144ºE, which is compatible with that of the neighbouring Torcal de Antequera massif. Bulk deformation affecting the Valle de Abdalajís massif was partitioned into strike-slip simple shear at the southern boundary and a triclinic transpressional component within the massif. Differences in strain partitioning pattern between these two massifs are unlikely related to flow partitioningLos patrones complejos de reparto de la deformación son muy comunes en la corteza continental. Suelen relacionarse con la cinemática de deformaciones tridimensionales y pueden analizarse mediante modelos de transpresión. En este trabajo, se evalúa el patrón de reparto del macizo del Valle de Abdalajís con el modelo de transpresión triclínica con extrusión oblicua. Estos resultados sugieren que el vector responsable de la deformación de la zona estudiada tendría una orientación NO75ºE-N144ºE, rango que es compatible con la orientación del mismo vector para el vecino macizo del Torcal de Antequera. La deformación que afectó al macizo del Valle de Abdallajís se repartió entre una componente de cizalla simple lateral en el límite sur y una componente de transpresión triclínica en la parte interna del macizo. Es improbable que las diferencias en los patrones de reparto de ambos macizos se puedan relacionar con un reparto del fluj