20 Structural Geology and Tectonics in a Quantitative World

Monday, 16 April 2018
1:30 PM - 5:30 PM
Room 275

CRITICAL WEDGES AND PENETRATIVE STRAIN: HOW DOES PENETRATIVE STRAIN ALTER THE CONCEPT OF A CRITICAL WEDGE?

Paper number: 20-4
Program: Theme Sessions
Time: 2:30 PM – 2:50 PM

Authors

Abstract

By definition, a critical wedge shows limited internal deformation, and, also by definition, penetrative strain is deformation occurring on a microscale within a deforming rock sequence. Critical wedge theory is typically used to understand the development of fold thrust belts, where variables such as the internal and basal friction, surface taper and dip of the decollement are taken into account. Numerical modeling shows that the minimum stable surface taper is dependent on the basal friction and the overburden, but that there are a range of possible tapers for a stable wedge, but critical wedges should not undergo penetrative strain.

This study presents a series of analog models tracking penetrative strain accommodation, where the overburden thickness is systematically varied over a constant basal decollement layer. Models are shortened to 5%, 10% and 15% respectively, creating a total of 9 experiments. Models were photographed from top and side view at each increment (1%) of shortening and side view photographs were used to measure surface taper.

We expected that the surface taper would increase with a thinner overburden, and this did occur in early model stages. However, in the latter stages of shortening and in the final configuration, models tended to the same surface taper, within the stable field, accommodated by varying amounts of penetrative strain. A model with a thinner overburden showed an increase in average penetrative strain within the overburden, relative to the comparison model with a thicker overburden from a previous experimental series. These results suggest that whilst critical wedge theory is a valuable construct for understanding the final configuration of a fold-thrust belt, the detailed behavior and development of the wedge cannot be understood without the inclusion of the penetrative strain concept.

Geological Society of America Abstracts with Programs. Vol. 50, No. 4

doi: 10.1130/abs/2018NC-312402

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.