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Abstract
Chapter from: M
65: Salt Tectonics: A Global Perspective
Edited By
M.P.A. Jackson, D.G. Roberts, and S. SnelsonAuthors:
J. Letouzey, B. Colletta, R. Vially, and J. C. Chermette Structure, Tectonics, Paleostructure
Published 1995 as
part of Memoir 65
Copyright © 1995 The American Association of Petroleum
Geologists. All Rights Reserved. |
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Letouzey,
J., B. Colletta, R. Vially, and J. C. Chermette, 1995, Evolution of salt-related
structures in compressional settings, in M. P. A. Jackson, D. G.
Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG
Memoir 65, p. 41-60. |
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Chapter
3
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Evolution
of Salt-Related Structures in Compressional Settings |
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J. Letouzey
B. Colletta
R. Vially
Institut Français
du Pétrole
Rueil-Malmaison, France |
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J. C. Chermette
Total
Paris La Défense,
France
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Abstract
Sandbox experiments
analyzed by computerized X-ray tomography provide relevant models of salt-related
contractional structures and improve understanding of the relative importance
of the many parameters influencing structural style. In front of thin-skinned
fold and thrust belts, the salt layers provide décollement surfaces,
which allow the horizontal strain to propagate far toward the edge of the
foreland. As shortening increases, older structures forming in front of
the system can be overtaken by out-of-sequence faulting and folding. The
very low friction coefficient of salt layers induces a symmetric stress
system. This promotes pop-up structures rather than asymmetric thrust faults.
Salt extrusions are related to former salt ridges or salt walls squeezed
by compression and dragged along thrust planes or to local low-pressure
zones along crestal tear faults during folding. The salt that spreads out
from the fault is rapidly dissolved. The resultant surface collapse structures
are progressively filled by a mixture of Recent sediments and reprecipitated
evaporites. Salt pinch-outs, either depositional or structural in origin,
are a major controlling factor of the deformation geometry in fold and
thrust belts. They trigger, either locally or regionally, contractional
structures, including folds and thrusts, in rapidly prograding passive
margins deforming by gravity gliding. In this structural context, salt
pinch-outs also thicken due to differential loading and gravity spreading.
The structural complexity in inverted grabens or in basement-involved orogenic
belts where salt is present is the outcome of many factors. The salt thickness,
the preexisting extensional structures, the synsalt and postsalt rifting,
and the related distribution of older salt structures and sediments all
localize folds and thrusts during later contraction. The relative orientation
of the former extensional structures to the younger shortening structures
largely controls the style of inversion (fault reactivation versus forced
folding and short-cuts). Salt is the main detachment level between the
folded cover rocks and the underlying faulted basement. However, secondary
detachments, which are common in the overburden, add further complexities--triangle
zones in the cores of anticlines and fish-tailed periclinal terminations. |
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