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Nappes and overthrusts are the mosl representative geological structures in mountain chains. The issue of their emplacement mechanisms and of the driving force of these displacements is a major problem in tectonics which interests, for near to a century now and not without harsh controversies, a significant proportion of structural geologists and geoscientists who work in the field of rock mechanics. This book attempts to give a clear and didactic synthesis of the current knowledge of the concept of thrusting, principally by tackling two approaches, mechanics and kinematics, which have proposed some solutions to this problem. At first (Chapter I), the notions of thrusting are defined, with the most recent terminology and the most important geometric aspects. This introduction to the geometry of thrusts is logically followed by the presentation of their problem; the issue of the emplacement mechanisms (Chapter 2). Let us note in passing that the formulation of the concept and the presentation of its problem are associated historically, which justifies presenting them in the historical framework of this discovery before tackling the different solutions and mechanical hypotheses. These are detailed in Chapter 3 by following a chronological progression, and emphasising the divergences and oppositions between different models so as to cover them fully. The chapter on the kinematics (Chapter 4) then returns to the type of data which can be collected in the field, by clarifying the relationships between displacement and internal strain.
List of contents
Preface. 1: The Concept of Thrusting. 1.1. Nappes, Thrusts and Fold-Nappes. 1.2. Thick and Thin-Skinned Thrusting. 1.3. Ramp and Flat Geometry. 1.4. The Concept of Displacement. 1.5. The Measurement of Displacement. 2: Background. 2.1. Historical Overview of the Discovery of Nappes. 2.2. The Problem of Nappe Emplacement. 3: Mechanics. 3.1. The Mechanical Paradox. 3.2. Resolution of the Mechanical Paradox. 3.3. Composite Models. 3.4. The Role of Erosion. 3.5. Classification of Emplacement Mechanisms. 4: Kinematics. 4.1. The Kinematics Approach. 4.2. Theoretical and Experimental Strain Patterns. 4.3. Displacement Trajectory. 4.4. Folding. 4.5. Emergent Ramp. 4.6. Lateral Ramps. 5: A Few Examples from the Alpine Chain. 5.1. The Internal Zone: Crustal Thrusts and Deep Nappes. 5.2. The Helvetic Nappes: Extrusion, Spreading and Ductile Gliding. 5.3. The Pre-Alps: Rigid Gliding. 5.4. Molasses: Testimony of Crustal Thickening. 5.5. The Jura: A Fold and Thrust Belt. 5.6. The Southern Alps: Rear Compression. Bibliography. Index.
About the author
Olivier Merle is a specialist in the relationship between deformation and displacement in nappes and thrusts. He has worked at the University of Arizona (USA) on thrusts in the Colorado Plateau and has carried out experimental research at the University of Texas at Austin. Olivier Merle was awarded the French CNRS Bronze Medal in 1992.
Summary
The chapter on the kinematics (Chapter 4) then returns to the type of data which can be collected in the field, by clarifying the relationships between displacement and internal strain.
