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Fold Model Set
Cat No - 1066604
Fold Model Set
This model set is composed of 8 pieces, which represent typically important folds and
faults that can be found on the Earth crust.
They are useful to understand the difference between plastic and elastic behaviour of a
rock. For this purpose the set includes different types of folds and faults.
Fig.2 - Fold classification
fold wall
fold plane
syncline
a)
anticline
Fig.1 - Fold Characteristics
When the rock layers are exposed to a stress, which is included in the plasticity range of
the rock, it will result in a rock creep that gives origin to different folds.
The plastic behaviour of the rocks can be ascribed to different causes. The pressure load
and the high temperature inside the shell operate on the rock layers determining plastic
behaviour.
Some rocks such as clay and gypsum present a typical low flow stress. Limestone as
well can be considered an excellent plastic rock, since it is well-bedded with clay layers. In fact the presence of many bedding planes of limestone and clay makes the folding process easier.
The fold is characterised by a core placed between two inclined walls: a fold plane can
be traced in the fold.
The wall slope is indicative of the folding process.
The classification of the folds is based upon structural elements.
In relation to the inclination of the fold plane, the folds are classified as
b)
c)
Fig.2 - Fold classification:
a) Straights folds. Inclination of the fold plane 90°
b) Inclined folds. Inclination of the fold plane <45°
c) Overturned folds. Inclination of the fold plane >45°
d) Flattened folds.
d)
Fold Model Set
Cat No - 1066604
Anticline is a system of folds convex to the top. Syncline is a system of folds convex to
the bottom. If the stress to which the rock layer is exposed is regular, the fold will be
straight.
If the stress to which the rock layer is exposed is not regular the fold will be asymmetric. A fold can develop into a fault.
If an overturned fold is exposed to a high-intensity or to a long-term stress, it can fracture on its flattened side, turning into a thrust fault. In this structure, called fault-fold, an
overthrust occurs.
Fig.3
overturned fold
The overthrust of the folds can lead to a structure in which the fold wall is preserved.
Otherwise the overthrust leads to a wall break. The development of a fold into a fault
determines a decrease in fold length (Fig.3)
overthrust fold
Key Card
1.
1.
13
4.
Rock layers not yet exposed to tectonic stress
5.
3.
4.
5.
6.
7.
8.
2.
6.
7.
syncline and
anticline with
Inclined fold with inclined fold plane
Inclined fold with stressed inclined fold plane
Inclined folds with parallel fold planes
Inclined fold developing into a flattened fold
Fault
Fold developing into a fault with overthrust
2.
Straight 8.
normal fold
fold with typical
plane