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Picture to left:
The scheme of
interrelation of foreland and hinterland parts of fold-thrust belt. The
example of island Taiwan
structure. The
picture after [Biq Chingchang. “Taiwan
island” // Mesozoic-Cenozoic orogenic belts. The Geological Society London
1974. Version after translation in Russian, 1977]
After colored: yellow part –
foreland (signs 1 – Mz basement of foreland, 2 –
Miocene, 3 – Pliocene), 4 - Pleistocene molasses, green part – hinterland
folding in sing 6 – upper Mz – lower Miocene
slates; red part
– sign 5 - Pz metamorphic complex.
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Foreland
Sediments.
Type: molasses, terrigenous deposits,
carbonaceous (limestone) layers.
Thickness of layers: from n0 meters up to n00 meters
Thickness of total cover: 1-5 km, 10 as maximal
Especial properties: The cleavage and metamorphism
are rare. Packages of hinterland types of sediments may exist after sliding
from upraised hinterland.
Folds.
Sizes: Usual width of folds (from hinge
to hinge) are 0,n - n km - near
thickness of total sedimentary cover. There are not fractal properties of
folds.
Type: “Parallel” style of large
folds. There are combinations of folds and thrusts.
Mechanisms: Mechanisms of separate fold
formation (buckling, flattening, flexural flow etc.) are enough for
description.
Shortening: Fold related shortening value
is not high (1,2 - 1,5).
Basement (Transcaucasian massif and
Scythian plate as example).
Type: There is rigid (in-deformable)
basement. It is part of a platform. It is main reason for existing of
sub-horizontal flat detachment between sedimentary cover units and the
basement. Magnitude of displacement of nappies is large (n-n0-n00 km)
as usual (not more than n-30 km for Alpine part of Greater Caucasus). The
folding of basements rocks took place much earlier only.
Typical tectonic forms
There are thrusts, large folds,
nappes etc. The detachment as boundary between sedimentary cover structure
and the basement is obligatory.
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Hinterland
Sediments.
Type: Slates, flysch, flysch-like
sediments, terrigenous, carbonaceous layers, alternation competent and
incompetent rocks.
Thickness of layers: from 0,01 meters up to 10-50
meters
Thickness of total cover: from 5 – 15, 20 km as
maximal
Especial properties: The cleavage and light
metamorphism (green shiest) are usual.
Folds.
Sizes: There are numerous small folds.
Usual width of folds of complex of folds (from hinge to hinge) are from 0,1 m up to 0,n - n km. It is
essentially lesser than total thickness of sedimentary cover. There are
fractal properties due to fractal properties of layering.
Type: “Similar” style of small
folds. Different size folded structures have hierarchic properties.
Mechanisms: Different size folded structures
have hierarchic properties and there are sets of mechanisms for each
type of different size structures.
Shortening: Fold related total shortening value
is high (1,5-3,0-5,0).
Basement (Grater Caucasus as example).
Type: The metamorphic basement has
viscous more than sedimentary cover rocks but 1-2 order more only. A large
folds (n km) and sub-vertical faults exist for partition surface basement-sedimentary
cover boundary. The rare local detachments exist only. Magnitude of
its displacement is local (0,n-n km) only. The
folding of basements rocks took place much earlier mainly, but a
remobilization of rocks exists also.
Typical tectonic forms
There are numerous folds and
complex of different size folded structure. There are thrusts and normal
faults. The detachment as boundary between sedimentary cover structure and
the basement is absent. Typical forms should be described yet.
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