45 research outputs found
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
Características físicoquímicas de sedimentos de lagunas situadas en las Zonas Externas de las Béticas Occidentales
In the western External Betics several temporal saline water bodies (playa-lakes) constitute singular environments that are pro-tected due to their ecological and hydrological values. Changes in their hydrological status due to both natural and human-induced changes alter the characteristics of their sediments. A detailed de-termination of the pH and electrical conductivity in the sediments of six playa-lakes within a range of degradation statuses was made in this study. The detailed examination of such geochemical variables has allowed us to establish three categories of degradation in the studied systems. Our results highlight the extreme vulnerability of this playa-lakes caused mainly by human activities, particularly tho-se related to land-use change for agriculture, as well as the necessity of its protection based on scientific criteriaEn las Zonas Externas de las Béticas occidentales varias masas de agua salinas temporales (lagunas tipo playa) constituyen ambientes singulares que se encuentran protegidos por sus valores ecológicos e hidrológicos. Las variaciones en su estado hidrológico debido a cam-bios naturales o inducidos por el hombre alteran las características de sus sedimentos. En este estudio se realizó una determinación de-tallada del pH y la conductividad eléctrica en los sedimentos de seis lagunas que presentan un rango variable de estados de degradación. El examen de tales variables geoquímicas nos ha permitido establecer tres categorías de degradación en los sistemas estudiados. Nuestros resultados destacan la extrema vulnerabilidad de estas playas causa-da principalmente por actividades humanas, particularmente aque-llas relacionadas con el cambio de uso de suelo para la agricultura, así como la necesidad de su protección con base en criterios científico
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