Earth inner forces

Crust continually affected by earth’s inner forces. The origins of such movements explain by two principle reasons. (i) Denser portion of earth tend to sink and squeeze the lighter portion between them. (ii)Liquefaction of the earth inner part allows melted materials to move towards to area of lower pressure.

The effect of these minor and major earth movements exhibits in rocks in the form of folding and faulting. If the original position of the bedrock has been changed but beds are still continuing, it refers as a folded. If the rocks break by displacement of plane of the fracture surface it will know as faulting. Due to the deforming stresses some rocks break easily than other rocks. Shale and similar rocks thin sediment layer often get these results of pressures. 

Fracture and flow

Rock flowage:

The rocks subjected to more stress it may responds in two ways. (i) They may crack and slip into lessened pressure positions, or (ii) it may flow into another form without any visible sign. Rock flowage occurs due to rearrangement of particles of the rocks. Rock flowage depends upon the nature of rock, pressure on it, the amount of pressure that applied and it distribution around the rock. 

Rock fracture:

When the rock cracks occurs it may fracture without any sign. Fracture result from shrinkage of sediments due to dry periods, compaction under load or diastrophic movements. Jointing or cracking without any movements is observe in thick shale. In limestone and sand stone not shows this evident. Generally cracks not exist in these rocks. They are tightly closed. Therefore it referred as ‘blind joints’. 

Folds and faults

Causes of folding

Folding occurs when rock layers compressed by different energetic forces. Rock layers deform from their original positions due to pressure gradients. 

Deeper in the earth, under very heavy lateral pressures and very heavy loads, strata are deformed by flowage. Folds due to this cause are complex and intricate detail than those produced by fracturing and slipping. 

All types of rocks subjected to this stresses. Igneous rocks and metamorphic rocks are subjected to folded and faulted than the sedimentary rocks. However sedimentary – rock relationship consider due to the study of fold and fault. 

The classifications of folds 

Monocline – This is a simple type of folded. It involves rocks bending. It causes downward dip in horizontal layers. The dip of layers high at folded axis. 

Anticline – An anticline arch upwards with youngest rock layers in upper part of the arch surface. In syncline fold that bends downwards and cause basin. In top of the dip contain youngest rock layers. 

Recumbent fold – It involves with parallel limps. This type of fold occurs due to highly directed pressure gradients compressed the folded on horizontal axial plane. 

When the rocks layers affected by forces from multiple directions they twists into variety of shaped. At this stage domes formed. If the beds downward away from central point that structure is dome. 

Examples:

Daxue Mountains – This Mountain formed on the eastern part of the Tibetan plateau during crustal folding in Jurassic periods. 

Verkhoyansk Mountains – This Mountain located in Russia and extend for 700 miles (1,100km). This range is anticline folded that is downward bends on its edges and upward bend on its center. It was formed in late Jurassic period and early cretaceous periods. 

Cape folded belt – This made up of 450 million years old sand stone and shale. During the building of super-continent pangea this mountain folded. 

Faults

 

Faults are unevenly distributed cracks in the crust and origins due to the movement between the opposing rock faces. Break in the rocks are relatively displacement parallel to the plane of the break. In surface slipping has taken places it known as fault plane. If the displacement area is wide and indefinite it called as fault zone. 

Faults are classified by the attitude of the fault plane, nature of the movement and direction of the motion. Movement can occur slowly and continuously or in large, sudden shifts that can leads to surface deform. 

Normal fault- Rocks one side of the fault slump below the other side. 

Reverse fault – The rocks on one side of the fault push upward above than other side. It accompanied by compression across the fault plane. When two side of a fault compressed they are squeezed together and hanging wall moves up the fault plane. 

Thrust fault – This action is similar to reverse fault and it origin at low angle. These faults stack on rock units and change the earth crust as thicker. 

Transform, or strike-slip, fault – Rocks two side of the fault slide and pass each other. 

Examples:

Anatolian fault – It’s a major transform fault crosses Turkey from east to west. 

Andaman fault – This is an Australian plate subduction-zone fault and in the strait that separate the Burma and Sumatra. 

Dead Sea fault zone – Connecting to the red sea spreading center in the south. This is a transform fault that allows sliding between the Arabian and African plates. 

References :

(1) Howard E Brown, Victor E monnett, J. Willis Stovall (1958); Introduction to Geology; Ginn    and Company; USA
(2) Michael Allaby, Dr. Robert R. Coenraads, Dr. Stephen Hutchinson, Karen McGhee, Dr. John O'Byrne, Dr. Ken Rubin (2008): The Encyclopedia of Earth, Sydney.
(3) D.M. preece, H.R.B. Wood (1946); Foundations of Geography; University tutorial press; London  
(4) http://202.116.83.77/hope/sites/geoscience2008/english/content/chapter5/content_05_01%28a%29.htm