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Book Chapter

The geometry and dimensions of fault-core lenses

By
Roy H. Gabrielsen
Roy H. Gabrielsen
Department of Geosciences, University of Oslo, Oslo, Norway
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Alvar Braathen
Alvar Braathen
Department of Geosciences, University of Oslo, Oslo, Norway
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Magnus Kjemperud
Magnus Kjemperud
Department of Geosciences, University of Oslo, Oslo, NorwayPresent address: Core Energy, Oslo, Norway
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Marie Lovise R. Valdresbr├ąten
Marie Lovise R. Valdresbråten
Department of Geosciences, University of Oslo, Oslo, NorwayPresent address: BP Exploration, Stavanger, Norway
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Published:
January 01, 2017

Abstract:

Field analysis shows that fault cores of brittle, extensional faults at a medium to mature stage of development are commonly dominated by lozenge-shaped horses (fault-core lenses) characterized by a variety of lithologies, including intact, mildly to strongly deformed country rock derived from the footwalls and hanging walls, various types of fault rocks of the protocatalasite and breccia series, breccia, fault gouge and clay smear. The lenses are sometimes stacked to form complex duplexes. These structures are commonly separated by high-strain zones of sheared cataclasite, and/or clay smear/clay gouge. The geometry and distribution of clay gouge in high-strain zones sometimes display evidence of intrusion, indicating high fluid pressure.

Although the sizes of the horses vary over several orders of magnitude, they frequently display a length:thickness (a:c) ratio of between 1:4 and 1:15.

The high-strain zones of fault rocks commonly constitute unbroken, 3D membranes that are likely to constrain fluid communication both across and along the fault zone.

There are significant contrasts in fault core architecture that are probably related to processes associated with contrasting fluid pressure, strain intensity and strain hardening/strain softening. Faults associated with strain softening are characterized by less abundant brittle deformation products and are less likely to be conduits for fluid flow compared to those that are affected by strain hardening.

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Contents

Geological Society, London, Special Publications

The Geometry and Growth of Normal Faults

C. Childs
C. Childs
University College Dublin, Ireland
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R. E. Holdsworth
R. E. Holdsworth
University of Durham, UK
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C. A.-L. Jackson
C. A.-L. Jackson
Imperial College, UK
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T. Manzocchi
T. Manzocchi
University College Dublin, Ireland
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J. J. Walsh
J. J. Walsh
University College Dublin, Ireland
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G. Yielding
G. Yielding
Badley Geoscience Ltd, UK
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The Geological Society of London
Volume
439
ISBN electronic:
9781862399716
Publication date:
January 01, 2017

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