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3D geometry and kinematic evolution of extensional fault-related folds, NW Red Sea, Egypt

By
Samir M. Khalil
Samir M. Khalil
Department of Earth Sciences, Fault Dynamics Research Group, Royal Holloway University of London, Egham, Surrey TW20 0EX, UKDepartment of Geology, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt
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Ken R. McClay
Ken R. McClay
Department of Earth Sciences, Fault Dynamics Research Group, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
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John Walsh
John Walsh
Department of Geology, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt
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Published:
January 01, 2017

Abstract:

Fault-related folds are common structural features found at a variety of scales in extensional settings, and have been recognized in both outcrop and subsurface studies. However, the detailed geometry and origin of complex 3D folds adjacent to normal faults are poorly known, and, in some cases, are interpreted to be due to strike-slip tectonics and post-rift contraction. Here we examine the 3D geometry of seismic-scale folds in a rift margin – the Red Sea – and discuss the interrelationship between the growth of normal faults and the development of their related folds. Detailed field mapping of the NW Red Sea rift system has shown that the rift margin is dominated by two large extensional fault systems formed by a series of linked NNW-, north–south- and NNE-striking fault segments. These linked segments exhibit distinct zigzag fault patterns and combine to form a number of NNW-trending faults that dip NE with dominant hanging-wall stratal dips to the SW. Hanging-wall stratal dips define 3D extensional fault-related synclinal folds in pre- and early synrift strata. The hanging-wall synclines are kilometre-scale, gently doubly plunging, with curved axial surface traces orientated sub-parallel to the bounding faults. Field data demonstrated that these folds are formed by along-strike variations in fault displacements, and they form transverse synclines combined with hanging-wall extensional fault-propagation folds. The complex 3D geometry of the hanging-wall synclines is the result of the along-strike segment linkage. Adjacent to the bounding faults, the stratal dips are sub-parallel to the faults as a result of extensional fault-propagation folding controlled by highly anisotropic pre-rift strata. Palaeo-strain analyses of fault-slip data, together with analysis of the fold geometry, clearly indicate that the faulting and folding in the NW Red Sea are formed by pure NE–SW extension during the Late Oligocene–Miocene rifting, and that contraction or strike-slip tectonics need not be invoked.

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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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Geological Society of London
Volume
439
ISBN electronic:
9781862399716
Publication date:
January 01, 2017

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