A review of deformation pattern templates in foreland basin systems and fold-and-thrust belts: implications for the state of stress in the frontal regions of thrust wedges
Résumé
Aesthetically appealing thrust systems and related large-scale anticlines, in both active and fossil foreland fold-and-
thrust belts, and the economic potential associated with the
m, have captured the interest of structural geologists for
many decades. As a consequence, a large amount of data on sub
-seismic deformation patterns from thrust-related an-
ticlines is available in the literature. We provide a review of deformation pattern templates from
fi
eld data in foreland
fold-and-thrust-belts and show that the most frequent tre
nds of sub-seismic syn-orogenic deformation structures
hosted in km-scale thrust-related folds frequently and pa
radoxically indicate a syn-th
rusting strike-slip stress
fi
eld con-
fi
guration, with a near-vertical
σ
2
and a sub-horizontal
σ
3
, rather than a contractional one where the latter is expected
to be the vertical principal axis of the stress ellipsoid. This a
pparent inconsistency between sub-seismic syn-orogenic
deformation structures and stress
fi
eld orientation is here named
“
the
σ
2
paradox
”
. Field data support a possible expla-
nation of the paradox, provided by the major role played by i
nherited early-orogenic extensional deformation struc-
tures on thrust fault nucleation. Nucleation of major thru
sts and their propagation is facilitated and driven by the
positive inversion and linkage of the early-orogenic sub-s
eismic extensional inheritance developed in the foreland
basin. This process eventually leads to the development of l
argereversefaultzonesandcanoccurbothincontractional
and strike-slip stress
fi
eld con
fi
gurations