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Analogue modelling of the Ainsa oblique zone in the Southern Central Pyrenees, Spain.

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Bibliographic Details
Title: Analogue modelling of the Ainsa oblique zone in the Southern Central Pyrenees, Spain.
Authors: van der Werf, Iris1 (AUTHOR) iris.van.der.werf@ltu.se, Schellart, Wouter P.1 (AUTHOR), Strak, Vincent1,2 (AUTHOR), van Agtmaal, Luuk3 (AUTHOR), Blankendal, Ruiz1 (AUTHOR)
Source: Journal of Structural Geology. Dec2023, Vol. 177, pN.PAG-N.PAG. 1p.
Subjects: Thrust belts (Geology), Orogenic belts
Geographic Terms: Pyrenees, Spain
Abstract: The Pyrenees are a collisional orogen striking WNW-ESE. However, in the Ainsa oblique zone in the south-central part of the Pyrenees, faults and folds rotate to ∼N–S over a westward thinning evaporitic layer. The influence of lateral change in basal friction due to declining evaporitic layer thickness in a fold-and-thrust belt is studied by analogue modelling simulating the Ainsa oblique zone. In the experiments the transition zone is simulated by a viscous silicone mixture sheet that laterally changes in thickness adjacent to frictional-plastic quartz-sand. The models confirm that a transition between weak and strong basal friction causes oblique structures to develop. Weak detachment zones are prone to fault propagation whereas strong detachment zones are prone to imbrication. At the transition zone those structural styles are combined, resulting in a complex domain. The differences in deformation style cause dextral shear and clockwise rotation in the transition zone and larger horizontal deformation propagation in the weak basal friction zone. Structures produced in the analogue models are compared to structures in the Ainsa oblique zone and found to be representative. Therefore, this study shows that transition between weak and strong detachment layers can explain the regional structural deformation style in the Ainsa oblique zone. • The Ainsa oblique zone has oblique fold and fault structures likely due to an unevenly distributed basal viscous salt layer. • A new analogue set-up simulates lateral progressive thinning of a viscous silicone sheet representing the Ainsa oblique zone. • Experimentally obtained oblique fold and fault angles over a thinning viscous sheet match the Ainsa zone structural angles. • Transition between high and low basal friction combines two deformation styles causing dextral shear and clockwise rotation. [ABSTRACT FROM AUTHOR]
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Abstract:The Pyrenees are a collisional orogen striking WNW-ESE. However, in the Ainsa oblique zone in the south-central part of the Pyrenees, faults and folds rotate to ∼N–S over a westward thinning evaporitic layer. The influence of lateral change in basal friction due to declining evaporitic layer thickness in a fold-and-thrust belt is studied by analogue modelling simulating the Ainsa oblique zone. In the experiments the transition zone is simulated by a viscous silicone mixture sheet that laterally changes in thickness adjacent to frictional-plastic quartz-sand. The models confirm that a transition between weak and strong basal friction causes oblique structures to develop. Weak detachment zones are prone to fault propagation whereas strong detachment zones are prone to imbrication. At the transition zone those structural styles are combined, resulting in a complex domain. The differences in deformation style cause dextral shear and clockwise rotation in the transition zone and larger horizontal deformation propagation in the weak basal friction zone. Structures produced in the analogue models are compared to structures in the Ainsa oblique zone and found to be representative. Therefore, this study shows that transition between weak and strong detachment layers can explain the regional structural deformation style in the Ainsa oblique zone. • The Ainsa oblique zone has oblique fold and fault structures likely due to an unevenly distributed basal viscous salt layer. • A new analogue set-up simulates lateral progressive thinning of a viscous silicone sheet representing the Ainsa oblique zone. • Experimentally obtained oblique fold and fault angles over a thinning viscous sheet match the Ainsa zone structural angles. • Transition between high and low basal friction combines two deformation styles causing dextral shear and clockwise rotation. [ABSTRACT FROM AUTHOR]
ISSN:01918141
DOI:10.1016/j.jsg.2023.104964