Analog Models of Fold-and-Thrust Wedges in Progressive Arcs: A Comparison With the Gibraltar Arc External Wedge
Metadatos
Afficher la notice complèteAuteur
Jiménez Bonilla, Alejandro; Crespo Blanc, Ana; Balanyá, Juan C.; Expósito, Inmaculada; Díaz-Azpiroz, ManuelEditorial
Frontiers in Media
Materia
Analog model Progressive arc Thin-skinned tectonics Strain partitioning Block rotation
Date
2020-03-31Referencia bibliográfica
Jiménez-Bonilla A, Crespo-Blanc A, Balanyá JC, Expósito I and Díaz-Azpiroz M (2020) Analog Models of Fold-and-Thrust Wedges in Progressive Arcs: A Comparison With the Gibraltar Arc External Wedge. Front. Earth Sci. 8:72.
Patrocinador
This study was supported by projects RNM-0451, EST1/00231, CGL2017-89051-P, PGC2018-100914-B-I00, and UPO 1259543.Résumé
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.