Structural geology is the study of rock structures and their deformation histories. The goal is to understand the stress fields that caused the observed strain and geometries in rocks. Structural features like faults and folds are important in fields like economic geology because they can form traps that concentrate resources like petroleum and metals. Geologists study these features by measuring the orientations and relationships of rock structures at outcrops.

1. Structural Geology
MODULE3

2. Structural geology is the study of the three-dimensional distribution
of rock units with respect to their deformational histories.
The primary goal of structural geology is to use measurements of
present-day rock geometries to uncover information about the history
of deformation (strain) in the rocks, and ultimately, to understand
the stress field that resulted in the observed strain and geometries.
Prepared by-
Prof. Basweshwar S. J.

3.  The study of geologic structures has been of prime importance in
 economic geology,
 petroleum geology
 mining geology.
• Folded and faulted rock strata commonly form traps that accumulate and
concentrate fluids such as petroleum and natural gas.
• Similarly, faulted and structurally complex areas are notable as permeable
zones for hydrothermal fluids, resulting in concentrated areas of base and
precious metal ore deposits.
• Veins of minerals containing various metals commonly occupy faults and
fractures in structurally complex areas.
• These structurally fractured and faulted zones often occur in association
with intrusive igneous rocks.
• Deposits of gold, silver, copper, lead, zinc, and other metals, are
commonly located in structurally complex areas
USE AND IMPORTANCE-
Prepared by-
Prof. Basweshwar S. J.

4. Outcrop
• An outcrop or rocky outcrop is a visible exposure of bedrock or
ancient artificial deposits on the surface of the Earth.
Features-
Outcrops do not cover the majority of the Earth's land surface
because in most places the bedrocks are covered by a mantle
of soil and vegetation and cannot be seen or examined closely.
However, in places where the overlying cover is removed
through erosion or tectonic uplift, the rock may be exposed, or crop
out.
Such exposure will happen most frequently in areas where erosion is
rapid and exceeds the weathering rate such as on steep hillsides,
mountain ridges and tops, river banks, and tectonically active areas.
Prepared by-
Prof. Basweshwar S. J.

5. • Most of the time, data collection
occurs in the field.
• Geologists record information
from a series of
different outcrops.
• An outcrop is simply a rock
column exposed at the surface,
• Naturally (because of erosion or
mountain building) or
• Artificially (because for instance of
a road cut, a tunnel, or an
excavation).
Prepared by-
Prof. Basweshwar S. J.

6. Prepared by-
Prof. Basweshwar S. J.

7. Strike and Dip
• Strike and dip refer to
the orientation or attitude of
a geologic feature.
• Planes can be defined in space by their
inclination or dip and their strike, the
bearing of the line of intersection of the
plane and a horizontal surface.
• The bearing of the projection of the dip on a
horizontal surface is in a direction at right
angles to the strike. This is called the dip
direction.
• Strike and dip, also known as the attitude of
a surface, are mainly used during the
geological mapping of an area.
Prepared by-
Prof. Basweshwar S. J.

8. • When a Rock layer is tilted, it could be tilted in
any direction.
• That intersection is the strike.
• This line (the strike) would make a unique angle
with respect to the (geographic) North.
• This angle can be measured in the field with a
compass, making it possible to plot the strike
and its orientation relative to the North on a
map.
• The strike is represented by the long arm of the
T in the T-symbol, and its angle to the North is
simply visible on a map because we are drawing
it on the map at that angle (remember that all
maps have North at the top).
Prepared by-
Prof. Basweshwar S. J.

9. • The dip is simply the angle of maximum
inclination of the strike layer.
• In the figure, we can see the strike,
represented by the black line (line of
strike) marking the intersection of the
tilted layer and the horizontal surface,
here represented by a body of water for
simplicity.
• We can also see the dip, which is the
angle (i.e. 30 degrees) of tilt with respect
to the horizontal surface, and which
points to the left (direction of dip).
Prepared by-
Prof. Basweshwar S. J.

10. Prepared by-
Prof. Basweshwar S. J.

11. Unconformities
• Unconformities are gaps in the geologic record that may indicate
incidents of crustal deformation, erosion, and sea level variations.
• They are a feature of stratified rocks, and are therefore usually found
in sediments.
• They are surfaces between two rock bodies that constitute a
substantial break in the geologic record.
• Unconformities represent times when deposition stopped, an interval
of erosion removed some of the previously deposited rock, and finally
deposition was resumed.
Prepared by-
Prof. Basweshwar S. J.

12. • Commonly three types of unconformities are distinguished by
geologists:
• ANGULAR UNCONFORMITIES
• DISCONFORMITIES
• NONCONFORMITIES
Prepared by-
Prof. Basweshwar S. J.

13. • Angular Unconformities are those where an
older package of sediments has been tilted,
reduced by erosion, and than a younger
package of sediments was deposited on this
erosion surface.
• Stages-
• First- Settling and
sediment deposition occurs;
• Second- Rocks are Uplifted and tilted
(deformation)
• Third- Erosion removes the uplifted
mountain range.
• Fourth- Subsiding occurs, the sea
covers the land surface, and new
sediments deposition.
Prepared by-
Prof. Basweshwar S. J.

14. • Disconformities are also an
erosion surface between two
packages of sediment, but the
lower package of sediments was
not tilted prior to deposition of
the upper sediment package.
• Stages-
• First- Setting and Sediment
Deposition.
• Second: uplift and erosion;
• Third: Renewed subsidence and d
eposition.
Prepared by-
Prof. Basweshwar S. J.

15. • Nonconformities are
unconformities that separate
igneous or metamorphic rocks
from overlying sedimentary
rocks.
• They usually indicate that a
long period of erosion
occurred prior to deposition
of the sediments (several km
of erosion necessary).
Prepared by-
Prof. Basweshwar S. J.

16. Inliers
• An inlier is an area of
older rocks surrounded by
younger rocks.
• Inliers are typically formed by
the erosion of overlying
younger rocks to make known
limited exposure of the older
underlying rocks.
• Faulting or folding may also
contribute to the
observed outcrop pattern.
Prepared by-
Prof. Basweshwar S. J.

17. Outliers
• An outlier is an area of younger
rock completely surrounded by
older rocks.
• An outlier is typically formed
when sufficient erosion of
surrounding rocks has taken
place to sever the younger
rock's original continuity with a
larger mass of the same
younger rocks nearby.
Prepared by-
Prof. Basweshwar S. J.

18. Overlap
• Overlap is the geologic phenomenon of successively wedge-shaped
younger rock strata extending progressively further across an erosion
surface cut in older rocks.
• It is generally associated with a marine misbehavior.
• It is a more general term than Onlap, in which the younger beds
overlap onto successively older beds. The opposite is offlap.
Prepared by-
Prof. Basweshwar S. J.

19. Faults and Folds
• A geological fold occurs when one or a
stack of originally flat and planar
surfaces, such as sedimentary strata, are
bent or curved as a result of
permanent deformation.
• Sedimentary folds are those due to
collapsing of sedimentary material
before it is solidifies.
• Folds in rocks vary in size from
microscopic waves to mountain-sized
folds.
Prepared by-
Prof. Basweshwar S. J.

20. Faults
• A fault is a crack in the Earth's crust.
• Typically, faults are associated with the boundaries
between Earth's tectonic plates.
• In an active fault, the pieces of the Earth's crust along
a fault move over time.
• The moving rocks can cause earthquakes.
Prepared by-
Prof. Basweshwar S. J.

21. CE SIGNIFICANCE
• Faults may pose problems of settlement, sliding, seepage and
seismicity and also landslides.
• Treatment depends on the type, nature and location of fault and type
of the civil engineering structures.
• Treatment include concrete plug, reinforced concrete plug, mat,
grouting etc.
Prepared by-
Prof. Basweshwar S. J.

22. • Joints can not be grouted closed or cemented over, especially if
building a embankment or a dam.
• Mainly because it is so difficult to map the full extent of the joints.
• Folds can cause variation in the depth and hardness of solid rock.
• Unconformity's, a beak in the uniformity of the soil or rock thus
affecting the safe placement of support structures and thus the future
stability of the building.
• A civil engineer would want to know the depth to basement rock, the
location of active faults within the project's footprint, and differences
in composition, or attitude of rock basement, inherent weaknesses
associated with joints, etc.
• The nature of the foundation beneath a civil structure could have an
important bearing on the way it should be designed, or even its
placement.
Prepared by-
Prof. Basweshwar S. J.