2. Course Rationale:
The course will cover
• An introduction structural geology and addressing tectonic stresses
impacting the lithosphere as a fundamental for deformation mechanisms of
the upper crust and formation of various types of sedimentary basins and
• Analyses of extensional fault systems, Strike-slip fault/shear systems and
their Orogenic belts and typical structures in contractional fault systems/
compressional deformational regime and their analysis,
• Analysis of dynamics of fold-thrust belts, fold mechanisms, and architecture
of reverse faults,
• Rift history analysis of the East African Rift valley
• The tectonic and metamorphic history of the East African Orogenic
At the end of the course students will:
will be able to understand the concepts and principles in structural geology
have the knowledge on the mechanism of deformation processes,
be able to recognize and analyze rock structures
3. Chapter One: Introduction to tectonic stresses
impacting the lithosphere
1.1. Introduction and application of structural geology
1.2 Stress and strain analysis
1.3 Brief review on mechanism of deformation
Chapter Two: Analyses of extensional fault systems,
2.1 Fault dynamics/growth, fault architecture, and
2.2 Methods for fault assessment,
Chapter Three: Strike-slip fault/shear systems and
3.1 Geometry of strike slip fault/shear system,
3.2 Analysis of Strike slip fault growth and fault architecture,
4. Chapter Four: Orogenic belts
4.1 Introduction to Structures formed in orogenic belts
4.2 Compressional deformational regime and their analysis in
4.3 Geometry and dynamics of fold-thrust belts
4.4 Fold mechanisms and architecture of reverse faults
4.5 The tectonic and metamorphic history of the East African
Chapter Five: Rift valley development stages
5.1 Rift initiation and driving forces
5.2 Rifting and volcanism
5.3 Rifting and sedimentary basin development
5.4 Rift history analysis of the East African Rift valley.
Course outline cont’d
5. Course Delivery: Teaching is carried out as lecture, literature
survey and seminars with compulsory attendance.
Course Assessment: continuous assessment including
assignments, seminars and presentations (50%) and final
Davis, G.H. and Reynolds, S.J. (1996) Structural Geology of Rocks and
Regions, 2nd Edition, John Wiley and Sons, Inc., New York, 776p.
Hatcher, R.D. (1995) Structural Geology: Principles, Concepts and
Problems, 2nd Edition, Prentice Hall, 525p.
Park, R.G. (1989) Foundation of structural Geology. Blackie and Son Ltd.,
Poblet, J. & Leslie R. J. (2011) Kinematic evolution and structural styles of
fold-and-thrust belts. Special Publication, Geological Society of London,
Kent C. Condie (1997). Plate Tectonics and Crustal Evolution. Elsevier Science; 294p
Ben A. van der Pluijm and Stephen Marshak (2004) Earth Structure: An Introduction to
Structural Geology and Tectonics. (2nd Edition); W. W. Norton & Company, Inc; 673p.
Stephen M. Rowland (2007); Structural Analysis and Synthesis: A Laboratory Course in
Structural Geology, 3rd Edition; Blackwell.
Storti, F. Holdsworth, R.E and Salvini F. (2003); Intraplate Strike Slip Deformation
Belts. Geological Society of London Special Publication No. 210; 243p.
• STRUCTURAL GEOLOGY is the study of the
architecture of rocks and regions that have developed
• Structural Geology can be defined as a branch of
geology concerned with the shapes, arrangements, and
inter-relationships of bedrock units and the forces that
• What we study in structural geology is strain and its
related translations and rotations.
• This is the end product of deformation.
• We never observe stress or the forces responsible for
• A famous structural geologist “John Ramsay” once said
that “as a geologist, I don’t believe in stress.
• This view is perhaps(approximatelly) too extreme—stress
certainly does exist, but we can’t measure it directly.
Stress is an instantaneous(happning immediately) entity; it exists only
in the moment that it is applied.
• In Structural Geology, we study geological materials that
were deformed in the past, whether it be a landslide that
formed two hours ago or a fold that formed 500 Ma ago.
8. 1.2 Definitions of Terminologies
The first stage of any structural analysis is a
description of the structures observed.
Since all 3D structures may be considered to be
arrangements of planes and lines in space this
involves the specification of the attitudes and
positions of planes and lines.
• Attitude: - the general term for the orientation of
a plane or line in space, usually related to
geographical coordinates and the horizontal.
Both trend and inclination are components of
• Trend: - the direction of a horizontal line
specified by its bearing or azimuth.
• Bearing: - a horizontal angle measured
east or west of true north or south.
– Eg. N 450W, N450E, S300W, S300E
• Azimuth: - a horizontal angle measured
clockwise from a true north.
– Eg. 0150,, 0450, 1500, 2200
• Strike: - the trend of a horizontal line on an
• Dip: - the inclination of a line of greatest slope
on an inclined plane. It is measured
perpendicular to the strike.
• Inclination: - the general term for the vertical
angle measured downward from the horizontal
to a plane or a line.
• Apparent dip: - the inclination of a line on an
inclined plane measured in a direction oblique to
the strike direction. It is always less than the
• Plunge: - a vertical angle from horizontal to a
line i.e. an inclination of a line.
• Pitch: - an angle between a horizontal line and
any line along an inclined plane.
• Stratigraphic way-up ( top or younging): - the
direction in which stratigraphically younger beds
or units are found.
• It is based upon a knowledge of stratigraphy and
of small scale sedimentary structures which
indicate the sequence of deposition e.g. graded
bedding, current ripple marks and others
14. • Structural way-up:- usually refers to the
bedding/cleavage relationships that indicates the
position with in a major folded structure.
• It is useful to recognize the presence and location of
major folded structures. The sketch below is a
representative sample that could show us the foliation/
bedding plane relationship under normally folded and
overturned bedding planes.
15. • In position 1 and 3, the cleavage plane is
steeper than the bedding plane.
• Structurally such relationship is called right way-
up, the hinge of a major antiformal fold is located
towards the right and the left, respectively.
• In position 2 the bedding plane is steeper than
the cleavage indicating an inverted sequence.
• The hinge of the major fold is towards the left.
18. • Example: Restoring Dipping Beds
– Rock sequence with angular unconformity
– determine the attitude of Group A prior to
deposition of Group B
• Group A (145°/26°), Group B (020°/30°)
19. Objectives of Structural Geology
• Structural geology is concerned with
deciphering three important problems:
– What is structure or deformation
– How does deformation (or deformation
movements) take place? How do rocks behave
– What is the cause of deformation? Under what
physical conditions did the structure form?
21. What is deformation or structure?
• RECOGNIZING and DESCRIBING the geometrical aspects of the
structure (primary, secondary, and contact)
• Recognition or description of structures may be based on;
– Aerial photo and remote sensing data interpretation
– Direct observation in the field
– Micro-fabric study in thin-section
– Drilling into the subsurface
– Geophysical monitoring and probing of the subsurface
– Laboratory study of experimentally deformed rocks etc.
• MEASURING and RECORDING the orientation of structural elements
• (physical and geometric elements), e.g. angles between lines and between
• This may include careful recording of data in notebook, making sketches,
taking pictures etc.
• This is the descriptive or geometric aspect of the structural
22. How does deformation take place?
How do rocks behave during deformation?
• EXAMINING and UNDERSTANDING the deformation
behaviour of rock (e.g. brittle, ductile, elastic, viscous
behaviour etc.) and the type of deformational
movements and changes (including distortion, dilation,
translation, rotation of the deforming body)
• EVALUATING and DETERMINING the structural
change in terms of extension, stretch, angular shear,
shear strain etc. (= STRAIN ANALYSIS).
• This is kinematic analysis of structures
23. What is the cause of deformation?
Under what physical conditions did the
• EXPLAINING and ANALYSING the type of stress field
responsible for deformation
• (e.g. the values of principal stress axes, normal and
shear stresses etc.)
• INTERPRETING and RECONSTRUCTING the physical
conditions prevailed during deformation
(e.g. P-T conditions, pore-fluid conditions, relation to
PLATE TECTONICS etc.).
• This is the dynamic analysis of structure. The basis for
dynamic analysis is theoretical and experimental
24. • In any case the following aspects are
emphasized in structural geology:
– Recognition of structures and their
– What to measure and record
– How to analyze and explain the data collected
– How to interpret and extrapolate the data and
incorporate in to regional synthesis of the
25. • For successful results of the above studies,
emphasis is placed upon:
– Systematic field observation (recognition
– Accurate measurements of the orientation of
– Careful recording of the data in the field
note book, and make sketches and taking
photos of structures.
– Continuous analysis and interpretation in
the field (also using stereonet).
27. 1.3 Recognition of Primary Structures and
The Two Categories of Fundamental Structures
– Contacts: - are boundaries that separate one rock
body from another.
• Normal Depositional Contact
– sedimentary layers and/or volcanic layers are
deposited on each other conformably, forming a
sequence of parallel to sub-parallel beds.
– Takes place during continuous deposition or during
separate events so close in time that the age
difference between the young and the older layers
cannot be detected with our existing time pieces.
– Normal depositional contacts are usually planar to
slightly irregular in form.
• Tectonic Contact
Unconformities have important tectonic implications.
It is a contact formed by brittle and semi brittle deformation
It could be fault (normal, thrust) or shear zone contact.
• Unconformity Contact
An unconformity is a depositional contact between two rocks of
measurably different ages.
There are about four types of Unconformities. These are:
29. Recognition of unconformities
A major problem is to distinguish unconformities from
tectonic (faulted) contacts. The following are some useful
• (i) Basal conglomerates (but beware of fault breccias).
The beginning of a new phase of deposition following
prolonged periods of erosion is commonly marked by
conglomerates -coarse-grained sedimentary rocks
consisting of generally rounded fragments. Commonly
these fragments are derived from the rocks that underlie
the unconformity, although this may not always be the
case. It is rare for conglomerates to occur everywhere at
the basal contact - they fill depressions in the surface on
which the new sequence is deposited.
30. • (ii) Radiometric or paleontological
dating, Under favourable circumstances
this will indicate clearly that the overlying
rocks are substantially younger than those
• Intrusive Contacts
Intrusions may be igneous or sedimentary rocks.
– The term “diapir” is used to describe any body that has been
able to flow as a fluid or solid state and can intrude the
surrounding country rock.
– Sedimentary intrusions are of two types:
Soft-sediment intrusions and salt diapirs.
– Soft-sediment intrusions involve the squeezing and/ or
buoyant rise of buried but yet-unconsolidated water-rich muds
and sands in to adjacent or overlying country rock.
– Salt diapirs are domes, pillars, and walls of salt that buoyantly
rise as rheids from thick beds of evaporates in to overlying
sedimentary country rocks.
They originate during the formation of the rock,
either through depositional processes or
Primary structures in sedimentary rocks form before
In volcanic and intrusive igneous rocks, primary
structures form during the flow and late stage
congealing of magma.
Metamorphic rocks do not possess primary
structures, for metamorphic rocks are made
secondarily at the expense of pre-existing
sedimentary, igneous or metamorphic rocks.
33. Primary sedimentary structures
• Sedimentary structures are those produced by the processes
of sedimentation and lithification.
• They provide the most widely used indicators of the way-up or
"facing“ directions of sedimentary successions.
• Stratification (Bedding ) ranges from massive layering to
delicate lamination, is a fundamental primary structure in
• Stratification is distinctive because of color, texture,
composition and resistance to physical properties.
• Stratification is caused by one or more of:
– seasonal changes
– catastrophic effects (storms, mud-slides etc.),
– current changes (directional, speed or both),
– source area disturbances,
– compensation level changes etc.
34. • Cross- stratification/Bedding
– found with in clastic
sedimentary rocks, in
siltstone and sandstone.
– It is characterized by
bedding or lamination
oriented at an angle to the
bedding surfaces that mark
the top and bottom of the
– The cross-beds or cross-
laminations are tangential
to the lower bedding
surface and they are
sharply truncated along the
35. • Ripple Marks
– Ripple marks are repeated wave forms of sand, silt,
and mud that are created in shallow water because of
the action of currents,
– Oscillation ripple marks have a symmetrical
concave form that reveals facing with in a
– Current ripple marks are asymmetrical, imparting a
polarity to the primary structure by which current
direction can be determined.
37. • Graded Bedding
– Some sandstones and conglomerates are
marked by zones of graded bedding, Since
the grain size becomes finer upward, graded
bedding constitutes a useful facing/younging
38. • Load Structures
– These are also primary sedimentary
structures developed as a result of density
difference between the overlaying coarser
material and the underlaying fine sediments.
– Load structures can be further classified as:
load cast and flame structures.
39. • Groove Structures: -
– Groove Marks are relatively long linear casts
produced by the scratching and plowing of
current of current-propelled objects across the
soft surface of mud.
– Flute casts: - are foot print shaped features
that taper from wide to narrow from toe to
41. Primary Volcanic structures
• Lava flow Structures
– Flow structures present in volcanic lava
commonly provide clues to movement plane
and facing. It forms in relatively low-viscosity,
pahoe-hoe basalts. Hollow, abandoned lava
tubes are preserved in the depth of flows, and
various blocky, ropy and pillow volcanic
• Breccia, Vesicles & amygdules, Pillow lavas
43. • Columnar Jointing
– The columns of basalt flow architecture are
produced by columnar jointing, a fracture that
accommodates negative dilation during final
congealing and shrinkage of a flow.
– Columns tend to be polygonal in the same
way that mud-cracks resulting from shrinkage
of mud are polygonal.
• Intrusive Bodies
45. Usefulness of Primary Structures
• Guide to strain
Primary structures, where found deformed, can be
valuable guides to internal strain.
Reduction spots are primary structures, and we have
already seen how they can be used to monitor the strain
• Distinguishing Up from Down
Many primary structures in sedimentary and volcanic
rocks can be used as guides for determining whether
rock layers are right side up or upside down. Telling “up”
from “down” with in a rock sequence constitutes the
determination of facing.
• Clues to Transport direction
Primary structures are useful in yet another way. They
some times display geometric properties that can
provide guides to kinematic movements that took place
during the deformation of rocks.
46. 1.4 Classification and Description of
• Secondary structures are structures that form in
sedimentary or igneous rocks after lithification
and in metamorphic rocks during or after their
formation due to stress.
• Secondary structures can be classified as:
• Penetrative -- characterizes the entire body of
rock at the scale of observation
• Non-penetrative -- Does not characterize the
entire body of rock
47. • At a relatively larger scale of
observation, the faults appear
To be widely spaced
At a small scale the faults can be
Considered to be penetrative
48. Structures can also be classified as:
• Brittle and Ductile
– Brittle Structures: - when elastic deformation leads
to failure; a material (rock body) loses cohesion by
the development of a fracture or fractures across
which the continuity of the material is broken, this
type of behavior is called Brittle Behavior and governs
the development of faults and joints.
– Ductile Structures: - ductile behavior in contrast
produces permanent strain that exhibits smooth
variation across the deformed sample or rock with out
any marked discontinuity. E.g folding of rocks.
49. • In describing the overall relationship of rock masses, the
fundamental secondary structures in nature are grouped
– Joints: - are planar cracks formed in response to tectonic and
thermal stresses. E.g. longitudinal joints.
– Shear fractures: - are cracks with slight sliding or shearing
parallel to the plane of fractures.
– Faults: - are discrete fracture surfaces along which rocks have
been offset by movement parallel to the fracture surfaces.
– Folds: - are structures that form when beds and layers are
transformed in to curved bent and crumbled shapes.
– Foliations: - are very closely spaced parallel planar alignments
– Lineations : - preferred linear alignments of features that
pervade rock bodies.
– Shear zones: - a tabular to sheet like planar or curvy-planar
zone composed of rocks that are highly strained than rocks
adjacent to the zone.
50. Structural Elements
• Structure is composed of structural elements that in turn
are identified and described, to permit us to carry out a
complete descriptive analysis.
• Structural elements are the physical and geometric
components of structures.
• The physical elements are real and tangible, and they
have measurable geometry and orientation.
– E.g., the folded layers are physical and real composed of the
rocks that have been folded. The hinge of a fold is also real,
fixed in position and contained in a real rock.
• The geometric elements are imaginary lines and
surfaces, invisible but identifiable in the field;
– they do have measurable geometries and orientations. E.g. the
axial surface and bedding-plane discontinuities are geometric
51. 1.5 Environment of Deformation: Structural Geology
Deformation takes place as a result of external
forces, the sources of which can be:
• movement of magma
• gravity of the earth or
• tectonic forces
52. • Tectonic forces are the most common
causes of deformation. The principal
forces and resistance that control plate
movements are: -
• Ridge Resistance(RR)
• Ridge Push (RP)
• Slap (or Trench) Suction (SS)
• Slab Pull or Negative Buoyancy (SP)
• Slab Resistance or Slab Drag (SR/SD)
• Mantle Drag (MD)
55. • Certain characteristic families of structures
are associated with particular tectonic
• Tectonic regimes are categorized into two
• Active plate margin regimes
• Intra-plate regimes
56. TECTONIC REGIMES MAJOR STRUCTURAL ELEMENTS
A. ACTIVE PLATE MARGINS REGIMES
Constructive plate margin (Mid-oceanic ridge); e.g.
Icelandic Rift system
Extensional fault system; strike-slip fault system
Conservative plate margin; e.g. San Andreas fault
system, Dead Sea transform fault
Strike-slip fault system
Destructive plate margin (Converging plate margin); e.g.
Japanese Island Arc system
Subduction complexes; Fold and thrust belt
Collision Zone; e.g. Himalayan collision zone Over-thrust sheet; fold nappies; strike-slip faults
B. INTRA-PLATE REGIMES
Passive Continental Margin; e.g. Western African
continental margin; Eastern American continental
Normal faulting; Syn-depositional structures
Continental Rift Zones; e.g. East African Rift; North Sea
Extensional (normal) faulting; Strike-slip systems
linking extensional faults
Intra-plate Strike-slip Zones; e.g. Northern Rocky
Major fault systems, associated en-echelon
Intra-plate fold and fault belts; e.g. Basin and Range,
Variable folding and thrusting; Extensional faulting
associated with regional uplift
57. APPLICATION OF STRUCTURAL GEOLOGY
Structural geology is applied:
To: understand how the rock units are interrelated in space and
time terms of
Change in status from original formation:
i.e. Change in shape, size, orientation, composition and etc.
The driving force of change recoded in rock architecture,
How and in what way did that change affect the original status
of the rock sequence,
What economic benefit or economic disadvantage has
that change for mankind comes to picture.
59. APPLICATION OF STRUCTURAL GEOLOGY……..
Structural geology is applied almost in every earth
resources evaluation and utilization/exploitation
1) In geological mapping
2) In mineral exploration
3) In mineral exploitation:
Under ground and surface mine development
4) In infrastructure development
5) In Hydro geological investigation and ground water
development and etc.
61. 1. APPLICATION OF STRUCTURAL GEOLOGY IN GEOLOGICAL
MAPPING AND MINERAL EXPLORATION
without architectural details,
the civil structure has no
Geological maps without
structural detail are like a
flesh without bone!
Hence Structural geology
is a back bone of
62. 2. APPLICATION STRUCTURAL GEOLOGY
FOR MINERAL EXPLORATION
Mineral deposits are controlled by a number of factors
The geological formations/ processes which can be a
source for the type of mineral we are looking for
If the mineralization is a result of secondary mobilization,
then it requires the medium of transport and
the place of concentration/deposition to form an anomaly
that can be of economic value
These all require the understanding of geological
63. STRUCTURAL GEOLOGY….. MINERAL
The distribution and extent of the geological formation
in stratigraphic sequence (primary structure)
The process of desolation of specific mineral from its
source area (micro structural deformation)
Transportation of dissolved mineral to site of
deposition (through secondary structural
discontinuities such as fault, shear zone;)
Place to deposit when physical conditions permit:
( potentially shear zones, geological contacts,
fault systems or zone; hinge zone of folds and
64. 3) APPLICATION OF STRUCTURAL GEOLOGY IN HYDRO
GEOLOGICAL INVESTIGATION AND EXPLOITATION
Ground water potential of an area is a function of:
porosity and permeability of the rock formation and
Trap of water flow in the rock formations.
Except sedimentary rocks (ex. Sand stone), most geological
rock formations have no or little primary porosity and
They have mostly secondary porosity and permeability such
(as Joints, faults, shear zones, foliation planes and etc).
(ex. Jointed basalt, jointed or sheared granite, foliated
gneiss and etc. are excellent ground water aquifers.)
Trap of the ground water flow for potential yield increase is also
a function of geological structures such as
intersecting faults and joints and etc.
Similar logic holds for oil exploration and exploitation.
65. 4) APPLICATION OF STRUCTURAL GEOLOGY FOR
INFRASTRUCTURE DEVELOPMENT/CIVIL WORK
Infrastructure development including:
tunnels for different purposes
need the understanding of geological structures and their
effect on the rock property (strength)
ultimately any factor that may hamper the stability and
eventual collapses of the structure.
Geological structures normally are fabrics that weaken
the strength of the rock mass and hence are potential
threats for the stability and suitability of civil structures.
66. APPLICATION OF STRUCTURAL GEOLOGY FOR CIVIL
Understanding the types of geological structures
affecting the rock mass, their orientation, intensity
analyzing their potential effect, one can alleviate
potential failure either
By predicting potential cause of failure and recommending
(including artificial treatment of the ground, change of the
site, recommending support system to ensure stability of
the civil structure).
Failure to understand the geological structure can
cause a catastrophic effect, damage of structure,
property and more so lose of investment
67. 5) STRUCTURAL GEOLOGY AND MINING
After exploration phase identifies deposit of
natural resources, mining follows.
Natural resources deposit may be located near
surface, or at the depth of surface.
We know that any deposit is controlled by
Hence, Mine development faces with the
ultimate reality of the geological structures that
control the mineralization.
68. APPLICATION OF STRUCTURAL GEOLOGY IN MINING
AND MINE DEVELOPMENT………
Depending on the nature of economic minerals deposit
and its location (depth from the surface)
Mining may be conducted as
surface mining or
Sub-surface (under ground mining)
Both mining methods are removal of rock mass from
its original position.
Both methods require the knowledge of structural
geology of the area.
69. MINING AND STRUCTURAL GEOLOGY……
Earths’ interior is constantly
under stress called in-situ
stress. The trajectory of
the stress field in the
is grid like;
Normally in undisturbed
condition, the earth is in
balance as a result of in-
situ stress and hence there
is no movement.
When we start mining we
start to disturb the balance
of in-situ stress and the
rock mass is prone for
70. STRUCTURAL GEOLOGY AND SURFACE MINING…
Surface mining requires design of mining to extract
maximum ore by excavation through minimum cost.
The design will have to include the study of rock
discontinuities (faults, fractures, joints, block size) etc so
that to determine:
Rock mass strength
1. For choice of mine opening and progression,
2. Choice of explosives, type, quantity (kg/ton), spacing
of drilling for blasting
3. For design of benches, stability of bench slope and etc.
4. determine the excavation method and equipment
71. SURFACE MINING……
Structurally less affected rocks are potentially lose, have
smaller block size, stable,
but require much more investment in terms of drilling
spacing, blast type and size to fragment the rock to
required size for processing.
Highly fractured rocks are unstable as a foundation, are
lose, and easy and less expensive to excavate
Understanding the configuration of geological
structures help in all design and choice of
parameters for economical surface and
undergraound mining and quarrying
72. APPLICATION OF STRUCTURAL GEOLOGY IN SUB-
Sub-surface mining is much more complicated than
Removal of rock mass (ore from the under ground
disturbs the stability of in-situ stress) and initiates
rock movement along discontinuities towards the
underground mine opening
73. It requires detailed understanding of geological structures,
their orientation, frequency which ultimately
determine the strength of the rock mass to be mined=>
help chose the right excavation technique
The stability of the walls and roofs of the adit=> help
the choice of the right support mechanism
The drilling and blasting design and inputs => help to
adopt the right designe and economical choice of
Excavation equipment and rate of mining and etc.
Identification of support system (type of support,
spacing of support like bolting, anchoring, etc) to
stabilize the mining process
74. Once you
know this you
Example 1: A guide to the applicability of excavation
techniques based on rock structure
75. Chose the
Eg. 2. Structural study to Chose the Drilling
and blasting design effectively