Fold–thrust structures – where have all the buckles gone?

Robert W H Butler,Mark A Cooper,Clare E Bond,Hannah Watkins

doi:10.1144/sp487.7

Robert W H Butler, Mark A Cooper + Show 2 more

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https://doi.org/10.1144/sp487.7

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Abstract

Abstract The margins to evolving orogenic belts experience near layer-parallel contraction that can evolve into fold–thrust belts. Developing cross-section-scale understanding of these systems necessitates structural interpretation. However, over the past several decades a false distinction has arisen between some forms of so-called fault-related folding and buckle folding. We investigate the origins of this confusion and seek to develop unified approaches for interpreting fold–thrust belts that incorporate deformation arising both from the amplification of buckling instabilities and from localized shear failures (thrust faults). Discussions are illustrated using short case studies from the Bolivian Subandean chain (Incahuasi anticline), the Canadian Cordillera (Livingstone anticlinorium) and Subalpine chains of France and Switzerland. Only fault–bend folding is purely fault-related and other forms, such as fault-propagation and detachment folds, all involve components of buckling. Better integration of understanding of buckling processes, the geometries and structural evolutions that they generate may help to understand how deformation is distributed within fold–thrust belts. It may also reduce the current biases engendered by adopting a narrow range of idealized geometries when constructing cross-sections and evaluating structural evolution in these systems.

Highlights

A key goal for many studies of continental tectonics is to relate folds, faults and distributed strain to create reliable geometric interpretations of threedimensional structure
Elsewhere we argue that this emphasis has created significant bias in the ways larger-scale structural interpretations are built and their uncertainties assessed (Butler et al 2018)
We examine the approaches through which current understanding of buckle folds has developed in parallel to these fold–thrust models

Summary

Introduction

A key goal for many studies of continental tectonics is to relate folds, faults and distributed strain to create reliable geometric interpretations of threedimensional structure. We challenge this notion, developing concepts of lateral fold growth inherent in buckling models, to argue that, even if illustrated by crosssections, structural understanding is better served through considering how deformation evolves in three dimensions.

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