folds
What is fold?
What is fold?
- Undulations
or waves in rocks formed by stratified formation such as sedimentary and
volcanic rocks or either metamorphosed equivalents.
1- Axial
plane: the plane that divides the fold symmetrically as possible and includes
hinge line
2- ¨Hinge
line: line formed by the intersection of axial plane and curved part of fold
May be classified according to:
Shape (straight , curved , irregular)
Position (verticle ,
inclined , horizontal)
3- Limbs:
the two sides of a fold that are divided by axial plane
4- Hinge
point: the point of maximum curvature of a fold
5- Fold
axis: the geometric lines on both sides of fold that are parallel to hinge line
6- Axial
trace : the line produced by intersection of axial plane and any other plane
Based on shape:
¨Anticline fold: convexing upward and has older rocks
in the core
¨Syncline fold: concaving
upward and has younger rocks in the core
¨Synform anticlinars e: it appesyncline but it has
older rocks in core like anticline fold
•
Dome form: layers dip in all directions away from the central point
•
Basin form: layers dip inward toward central point
•
Monocline: local steepening with homocline
•
chevorn
Based
on tightness (Fleuty classification):
•
Gentle fold : 170 : 180
•
Open fold : 90 : 170
•
Tight fold :
10 : 90
•
Isoclined fold : 0 : 10
Based on scale:
folds can present in all scales:-
1-Microscopic (require magnification)
2-Mesoscopic
(specimen and outcrop size)
3-Macroscopic(larger scale)
•
Fold orders:
First order : largest fold in given area
Second order : smaller folds found on the limbs
of first order fold
Mechanism of fold
•
Folds : are the signatures of deformation forces that
result from plate tectonic. The term fold implies that an originally planer
structure, such as sedimentary bed, has been bent
•
In plate tectonic(convergence) continental with
continental will not occur subduction but occur colloid to each other forming
mountain range of folded rocks.
•
Another example of convergence of plat
•
tectonic: oceanic with oceanic , in it will occur
subduction among the two layers.
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