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The development of sheath folds in viscously stratified materials in simple shear conditions: An analogue approach.

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Title: The development of sheath folds in viscously stratified materials in simple shear conditions: An analogue approach.
Authors: Dell'Ertole, Damiano1 Damiano.DellErtole@monash.edu, Schellart, Wouter P.1
Source: Journal of Structural Geology. Nov2013, Vol. 56, p129-141. 13p.
Subjects: Sheath folds (Geology), Stratified flow, Shear (Mechanics), Geologic faults, Viscous flow, Deflection (Mechanics)
Abstract: Abstract: Sheath folds are highly non-cylindrical folds occurring in a variety of geological settings, and have been studied using different approaches. With the present work, we provide a quantitative analysis of the generation and development of sheath folds in a viscously layered system in simple shear conditions. The sheath folds develop from an initial non-cylindrical deflection located on the highly viscous layer. The analogue experiments investigated the influence of (1) variations in the viscosity ratio between the high viscosity layer and the matrix (η hvl/η m ), (2) variations in the ratio between the amplitude of the initial deflection and the thickness of the high viscosity layer (A f /T hvl), and (3) progressive simple shear (γ). The results show that increases in η hvl/η m will produce progressively less elongated sheath folds, while increases in A f /T hvl will result in more elongated sheath folds. We present regime diagrams with η hvl/η m and A f /T hvl for different shear strains illustrating under which conditions sheath folds form. In case the original deflection amplitude and layer thickness as well as γ can be retrieved for sheath folds in nature, then their geometry can be used to quantify the effective η hvl/η m . [Copyright &y& Elsevier]
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Database: Engineering Source
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Abstract:Abstract: Sheath folds are highly non-cylindrical folds occurring in a variety of geological settings, and have been studied using different approaches. With the present work, we provide a quantitative analysis of the generation and development of sheath folds in a viscously layered system in simple shear conditions. The sheath folds develop from an initial non-cylindrical deflection located on the highly viscous layer. The analogue experiments investigated the influence of (1) variations in the viscosity ratio between the high viscosity layer and the matrix (η hvl/η m ), (2) variations in the ratio between the amplitude of the initial deflection and the thickness of the high viscosity layer (A f /T hvl), and (3) progressive simple shear (γ). The results show that increases in η hvl/η m will produce progressively less elongated sheath folds, while increases in A f /T hvl will result in more elongated sheath folds. We present regime diagrams with η hvl/η m and A f /T hvl for different shear strains illustrating under which conditions sheath folds form. In case the original deflection amplitude and layer thickness as well as γ can be retrieved for sheath folds in nature, then their geometry can be used to quantify the effective η hvl/η m . [Copyright &y& Elsevier]
ISSN:01918141
DOI:10.1016/j.jsg.2013.09.002