STRUCTURAL GEOLOGY

BY

A. S. Abu Sharib

Notes in

What is the structural geology and

Tectonics?

It is that branch of geology that deals with deformation of the rocks on the micro -, meso -, and macroscopic scales.

Structural geology and tectonics has undergone rapid development since 1960 s. Structural geology has changed from an almost purely descriptive to a quantitative one.

New insights into the process of deformation and formation of structures at a wide variety of scale have become possible through the application of the theoretical principles of continuum mechanics that is the study of how bodies of different materials are deformed when subjected to forces .

Simulating rock deformation in labs, under conditions very close to geologic reality, based on thorough observations of the structures enhances our understanding of how structures develop.

Structural geology and Tectonics depend on other branches of geology such as geophysics, petrology, metamorphic geology, sedimentology, paleontology, geochemistry

Why do we study structural geology ?!

It is very important in oil, water and ores exploration.

To know how and under what conditions, the different types of

structures form.

Together with tectonics, it throws light on mountains building processes

and the evolution of the planet Earth.

Deciphering the driving forces that were active during the mountain

Building

To avoid natural hazards as possible !

To build safe constructions and in big city planning and siting (October,

East Beni -Suef, El Qattamiya cities i.e. the most safe place for

construction

Should I dig here or there !!

? ?

Where is the Oil

???

Well done

Time =

Oil, Gas, Water

Exploration

Mountain building processes

Evolution of the Earth

Rocky mountains

Himalaya

Alps mountains

Structural Geology vs. Tectonics

Structural geology and tectonics are concerned with the reconstruction of the inexorable motions that have shaped the

Both are closely related in both their subject matter and their approach to the study of the evolution of the Earth.

Both are concerned with the study of the history of active or past

They differ in that Structural Geology deals with the study of deformation at a scale ranging from submicroscopic to the regional whereas the Tectonics predominantly deals with a regional to global scale.

Both branches are interdependent and at the regional scale, Structural Geology and Tectonics overlap.

It is really important to know that !!

A) Descriptive Recognize and describe carefully the structures in the rock

etc ) by

measuring their location, orientation and geometries.

Complete analyses of the structures should go through the

following steps

B) Kinematics Studying the deformational movements / motions that produced these structures i.e. Translation, Rotation, Distortion, Dilation

C) Kinetics / mechanical Studying the driving forces responsible for these structures or the interaction between forces and motions that lead to the geometry of the observed structure.

Fundamental concepts

Before going through structural geology, there

are some fundamental concepts a structural

geologist should be aware of :

(1) Law of Uniformitarianism

James Huton

(2) Law of multiple working hypotheses

According to this law, The contact between the igneous body and the overlying sedimentary rocks can be :

(1) An intrusive contact

(2) A fault contact

(3) An unconformity contact

(3) Law of original Horizontality

Horizontal strata Inclined strata

(4) Law of Superposition Within a layered sequence, commonly sedimentary rocks, the oldest

rocks will occur at the base of the sequence and successively younger

rocks will occur towards the top, unless the sequence has been inverted

(5) Law of Cross -cutting relationship that is, a fold or fault must be

6 1 2 5 4 Faulting Unconf. 3

1

2

3

1

2

3

4

2

1

1

2

3

(6) Law of Faunal Succession

the A

dva

ncin

g

More Advanced

Less Advanced

(7 orientations of larger structures of the same generation

within

These are structures of primary origin not related to any tectonism or deformation

They are very important in determining the facing ( younging direction) in a sequence of rocks to ascertain if the sequence is upright or overturned

In some cases, interpolating thoroughly helps in extrapolating regi onal structures

They comprise :

Primary sedimentary structures: that were developed during sedimentation

Igneous primary structures: that were developed before the solidification or the crystallization of the igneous body.

Non -tectonic (primary structures)

Structures that are deformation -related are commonly seen cross cutting original primary structures and are called secondary (tectonic) structures. They post -date the sedimentation of sedimentary rocks and crystallization or solidification of igneous rocks

Non -tectonic (primary sedimentary structures)

(1) Bedding