DESCRIPTIVE ANALYSIS
 
 

KINEMATIC ANALYSIS

is the reconstruction of movements that take place during the formation and deformation of rocks

DYNAMIC ANALYSIS

interprets stresses to describe the forces from which they were derived and the relationship between stress and strain
 
 

REVIEW

JOINTS
 
 

DEFINITIONS
 
 

READINGS CH.2 ESPECIALLY P. 29 PIZZA ANALYSIS. CH.3 CH.4

LECTURE
 
 

Until now we have been learning to recognize and describe structures e.g., tilted similar folds and making geological maps: this is known as descriptive analysis

 We have also examined how those structures are formed geometrically. Are they formed by a rotation? or simply a translation? or is there some amount of internal deformation? What are examples of each? This procedure is known as kinematic analysis. Kinematic analysis focuses on interpreting the deformational movements responsible for the development of structures.

We have seen a little why the deformation is taking place in terms of forces and stresses. ( Andersonian faulting, Mohr-Coulomb fracture diagram) This part requires using experimental results and theoretical calculations. This procedure is known as dynamic analysis.

Kinematic Analysis- Discussion

Q. But, what is deformation?

 A. A change in the shape, position, form or volume.

Q. Can an object undergo deformation but not change its shape and only its position? Y

 Q. Are plates being deformed? Y

 A. Plates experience local changes of shape at their edges where most of the deformation takes place. On the scale of the plate, internally the plate is rigid and does not deform. When objects have no internally deformation and only undergo a rotation or a translation we say the deformation is rigid.
 
 

An example of nonrigid deformation is exemplified by sigmoidal tension gashes:

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 we know that this shape is formed by a progressive rotation and simultaneous growth of the tension fracture. However, these definitions are also a question of scale because if you looked at the ongoing deformation on a large enough scale you may perhaps only seen translation of two rigid blocks across a fault. If we did not have markers such as the quartz filling in the fractures we would not be able to compare the changes in angles between the crystals inside the quartz fracture and the material outside the zone of deformation.

STRAIN

 Non-rigid body rotation is particularly important when we deal with the concept of strain. Strain is internal deformation. Trying to describe strain mathematically can be very difficult. It is often common to at least initially assume that the type of strain is very simple, i.e. it is the same throughout, that it is uniform throughout the body. And if we find that this assumption is not the most appropriate we can break up the body we are studying into smaller parts inside which the assumption holds true.

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Quantification of strain is important because it can predict other geological processes. For example, using a homogeneous deformation model, if whole lithospheric thinning exceeds 300% theoretically by some calculations, volcanism may occur.
 
 

How do we quantify extension in rifted margins?

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Dynamic Analysis- Discussion
 
 

In Geology you will always hear of the use of stress instead of force Why?

 In the earth what forces are responsible for bending rocks? faulting rocks? Why can a rock hammer break a rock but buildings constructed on basement rock not break the underlying rock?