Earth Structure: An Introduction to Structural Geology and Tectonics

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The Hashemite University Faculty of Natural
Resources and Environment Dept. of Earth and
Environmental Sciences STRUCTURAL GEOLOGY
(111201350) 3 CH (23) Lecturer Dr. Masdouq
Al-Taj E-mail maltaj_at_hu.edu.jo
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EARTH STRUCTUREAn Introduction to Structural
Geology and Tectonics2nd edition

• Authors Ben A. Van der Pluijm Stephen Marshak
• Publisher Norton, 2004

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Other References

• Park, R., (1997) Foundations of structural
  Geology. Chapman and Hall, London.
• Hobbs, B., Means, W. and Williams, P., (1989)
  An outline of structural geology, 3rd ed., John
  Wiley, New York.
• Ramsay, J. and Huber, M., (1987) The techniques
  of modern structural geology. Academic Press,
  London.

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INTERNET REFERENCES http//www.uwrf.edu/iw00/Str
uctural_Geology.html http//www.geo.cornell.edu/ge
ology/classes/RWA/GS_326/GEOL326.html http//earth
.usc.edu/geol321/ http//www.geo.cornell.edu/geolo
gy/faculty/RWA/maintext.html http//www.geologysho
p.co.uk/struct1.htm
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EXAMS First exam 15 Second exam 15 Final
exam 40 Lab. quizzes attendance 30
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In this course we will cover three parts of the
text book

• PART A Fundamentals
• Chapter 1 Introduction
• Chapter 2 Primary and Nontectonic Structures
• Chapter 3 Force and Stress
• Chapter 4 Deformation and Strain
• Chapter 5 Rheology

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• PART B Brittle Structures
• Chapter 6 Brittle Deformation Processes
• Chapter 7 Joints and Veins
• Chapter 8 Faults and Faulting
• PART C Ductile Structures
• Chapter 9 Ductile Deformation Processes and
  Microstructures
• Chapter 10 Folds and Folding

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• OBJECTIVES
• The aims of this course are
• Introduces the basic mechanical principles in
  structural geology, like stress, strain, elastic
  and plastic deformation in materials and rocks.
• Enables the student to recognize and describe
  the different geological structures (joints,
  faults, folds, foliationetc.).
• Study the mechanism of the formation of
  different structures.
• Helps the student to determine time-structural
  event relationships.
• Review the skills of using the geological
  compass and the stereographic methods in
  structural geology.
• Study geological structures in the lab and in
  the field through field trips to the surrounding
  areas.

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Week Subject Chapter
1 Introduction and basic terms in structural geology 1
2 Primary and nontectonic structures 2
3 Force and stress Normal and shear stress 3
4 Mohr diagram for stress 3
5 Strain measurement 4
First exam
6 Rheology 5
7 Brittle deformation processes 6
8 Initiation of brittle deformation 6
9 Joints 7
10 Faults and faulting, Fault systems 8
11 Recognizing and interpreting faults 8
Second exam
12 Ductile deformation processes and microstructures 9
13 Folds 10
14-16 Fold classification 10
14-16 The mechanics of folding 10
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CHAPTER ONE Introduction 1.1 Historical Survey

• Leonardo de Vinci (1452-1519) drew carefully
  shape of rock bodies in sketches to understand
  the natural shape of the Earth.
• Perhaps the first description of rock deformation
  came in the 17th century by Nicholas Steno
  through the principle of original horizontality.
  He examined outcrops and observed that the
  bedding of the rocks wasnt horizontal. So, he
  recognized these rocks were (dislocated)
  deformed.

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• During the late 18th century and through the 19th
  century the geological discovery have been
  quickened.

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In 1785, James Hutton introduces the doctorine of
uniformitarianisim (the present is the key to the
past). A group of scientists started to
recognize themselves as geologists. Their main
aims were To make geological maps.
Reported the formation of rocks. The
origins of specific structures and
mountain ranges. Later, ideas about the origin
of mountains have evolved gradually.
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• Firstly, they believed that movement of magma
  upward generated mountains and the associated
  folds were generated by down-slope movement along
  the flanks of these mountains. (G. P. Scrope
  (1825)).

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• Subsequently, horizontal forces were emphasized,
  and the scientists were believed that mountain
  ranges evolved due to contraction of the earth
  that resulted from the progressive cooling.
• Later, James Hall recognized that the Paleozoic
  strata in the Appalachian in North America were
  much thicker than correlative strata in the
  interior of the continent. This led to the
  development of geosyncline theory where deep
  subsidening sedimentary basin evolved into
  mountain range.

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• In the 20th centaury, the foundations of
  structural geology solidified, but by the 1960s
  it became a real science by the formulation of
  PLATE TECTONICS THEORY and considered as a
  revolution in earth sciences.

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• This figure after Isacks et al., 1968.

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Structural geology is the study of the
three-dimensional (3 D) distribution of rock
units with respect to their deformational
histories. The primary goal of structural
geology is to use measurements of rock to get
information about the history of deformation
(strain) in the rocks, and ultimately to
understand the Forces (stress field) that
resulted in the observed deformation.
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This understanding of the stress field can be
linked to important events in the regional
geologic past a common goal is to understand the
structural evolution of a particular area with
respect to regionally widespread patterns of rock
deformation (e.g., mountain building, rifting)
due to plate tectonics.
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WHAT IS THE JOB OF STRUCTURAL GEOLOGISTS (1)
measure rock geometries. (2) reconstruct their
deformational histories. (3) calculate the
stress field that resulted in that
deformation.
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1.2 GEOLOGIC STRUCTURESFirstly, let us define
what we mean by geologic structure It is a
geometric feature in a rock whose shape, form and
distribution can be described. Examples of
geologic structures are folds, faults , joints,
veins, cleavage, foliation and lineations.
Consequently, there are many schemes for
classification of these structures.
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1.2.1 Classification of Geological Structures

• I. Classification based on geometry (shape and
  form of a particular structure)
• a. planer surface
• b. linear surface
• c. curviplaner surface
• This classification may be the most important
  because it includes folds, faults , joints,
  veins, cleavage, foliation and lineations.

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II. Classification based on geological
significance

• a. primary ripple mark, cross bedding, mud
  cracks.
• b. local gravity-driven slumping.
• c. local density inversion driven salt dome
  (form due to variation in rock density).
• d. fluid-pressure driven injection of
  unconsolidation material due to sudden release of
  pressure.
• e. tectonic due to interaction between
  lithospheric plates.
• First four usually primary and nontectonic
  structures while the fifth is the main aspect of
  structural geology.

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III. Classification based on timing of formation

• a. synformational structure forms with initial
  deposition of rock.
• b. penecontemporaneous structure forms before
  full lithification, but after initial deposition.
• c. postformational structure forms after the
  rock has fully lithifide.

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IV. Classification based on Process of formation
(the deformation mechanism)

• Fracturing related to cracks in rocks.
• Frictional sliding related to slip of one body
  of rock past another.
• Plasticity deformation by internal flow of
  crystals without loss of cohesion.
• Diffusion material transport in either
  solid-state or assisted by a fluid (dissolution).
• Combination combinations of deformation
  mechanisms contributing to the overall strain.

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V. Classification based on Mesoscopic
cohesiveness during deformation

• Brittle structure forms by loss of cohesion.
• Ductile structure forms without loss of
  cohesion.
• Brittle/ Ductile deformation with both brittle
  and ductile aspects.
•  

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VI. Classification based on Strain significance,
in which a reference frame must defined (usually
earth surface or the deformed layer)

• Contractional shortening of a region
  (convergence).
• Extensional stretching of a region (divergence).
• Strike-slip movement without either shorting or
  stretching (lateral slip).
•  

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VII. Classification based on Distribution of
deformation in a volume of rock

• Continuous occurs at the rock body at all
  scales.
• Penetrative occurs throughout the rock body at
  observation scale.
• Localized structure in continuous or penetrative
  only within a definable region.
• Discrete structure occurs as an isolated feature.

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Finally, most crustal structures are a
consequence of plate tectonics activities that
include convergence, divergence and transform
(lateral slip) movements.
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1.3 Stress, strain and deformation

• Stress is the main cause of deformation in the
  crustal rocks.
• The stress (s) is the force (F) per unit area
  (A) of the acting plane s F / A
• Stress(s) force/area
• massacceleration/area
• kg.m.s-2/m²Newton/m²
• N/ m²Pascal (Pa)
• Sign of stress
• ve in case of compression.
• -ve in case of tensions.
• Deformation refers to any change in shape,
  position, or orientation of a body resulting from
  the application of a differential stress.

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• Deformation in general has three components -
• Translation movement of rock from place to
  another ( i.e fault)
• Rotation pivoting of a body around a fixed axis
  (i.e fold)
• Strain change in size (dilation) and/or change
  in shape (distortion) of a rock.

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Strain is of two types 1.
Homogeneous strain the deformation is the same
throughout the rock. 2. Heterogeneous strain
the deformation is different throughout the rock.
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• 1.4 Structure analysis
• What do structural geologists do?
• Structural geologists do structural analysis,
  which involves many activities such as
• Descriptive analysis
• The characterization of the shape and appearance
  of geologic structures.
• Attitude, strike, dip angle, dip direction
  ,plunge, trend, rake (pitch), apparent dip,
  trace, cross section, profile plane, position,

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2. Kinematic analysis Involve the determination
of the movement paths that rocks or parts of
rocks have taken during transformation from the
undeformed to deformed state. (use of features in
rocks to define the direction of movement on a
fault).
3. Dynamic analysis Involve development of an
understanding of how stress related to
deformation (stress and its direction). 4.
Strain analysis The development of mathematical
tools to quantifying the strain in a rock.
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5. Deformation Mechanism analysis The study
of processes on the grain scale to atomic scale
that allow structures to develop , ex sliding,
fracturing, plasticity. 6. Tectonic analysis
The study of the relation between structure and
global tectonic process divergent, convergent,
transport.
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Structural Analysis and Scales of Observation

• 1. Descriptive analysis (shape and appearance,
  vocabulary, 3D orientation).
• 2. Kinematic analysis (define the direction of
  movement)
• 3. Strain analysis (quantifying the strain
  (maths)).

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• 4. Dynamic analysis (How stress is related to
  deformation, used microstructure).
• 5. Deformation mechanism analysis (structural
  development in grain to atomic scale, fracture
  and flow of the rock).
• 6. Tectonic analysis (relation between structure
  and global tectonic).

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We used four relative scales of observations

• Scale of observation
• 1. Micro scale (thin section) microscope
• 2. Meso scale (isolated outcrop) hummer
• 3. Macro scale (regional) helicopter
• 4. Mega scale (plate) Satellite, Global
  Positioning System (GPS)

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• Good observation, recognition and description of
  rocks and their structure are very important for
  field analysis.

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Some guideline for the interpretation of deformed
area

• Law of original horizontality (bed deposited
  horizontally).
• Law of superposition (strata follow one another
  in chronological).
• Stratigraphical continuity for the same
  lithological sequence.
• Sharp discontinuities in lithological pattern are
  faults, unconformities or intrusive contacts.

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• Deformed area can be subdivided into a number of
  region contain consistent structural attitude
  (structural domain).
• Principle of least astonishment (simplest
  interpretation is most correct).
• Additional subsurface data (drilling, seismic and
  other geophysical techniques) are important for
  structural geologist interpretation.
• It is important to imagine all geological
  structure in a MODEL 3D and even more than that.