ES2202: Basic Structural Geology & Tectonics
Lecture1: Introduction
IISER Kolkata Spring, 2017
What caused the changes in these rocks?!
Forces?!
Relative movement of lithospheric plates:
Convergent boundary (C)
Divergent Boundary (D)
Transform boundary (L)
Layers that are not presently horizontal must have been some way deformed !
Principle of Original Horizontality
Nicholas Steno (17th Century)
Deformation?
Total Displacement field: 1. Bulk Translation
2. General Deformation Rigid Body Rotation
Strain
All of these quantities are independent of each other
Deformation
Components of Deformation
Translation
Rotation Strain
Geologic Structure: Any definable
shape/fabric in a rock body
(a) Primary structures
Form during or shortly after deposition
of sediments/formation of rocks
(b) Secondary structures
- Tectonic structures: Form in response
to forces generated by plate
interactions.
Structural Geology
& Tectonics?
What?
How?
Why?
What is Structural Geology?
The study of the architecture of rocks
from submicroscopic to regional
scales, resulting from deformation.
Tectonics
Same as Structural Geology but at
a larger scale
(e.g., regional to global scale)
Wow! How do I
describe this?
How did it
form?!
Rock Deformation
Geometric analysis:
Characterization of shape & appearance of geologic structures
Developments of methods for uniquely describing the orientation of structures
in 3D space
How did the structures form?
A. Kinematic analysis
Motions that produced the structures
Determination of movement paths of rocks during transformation from
undeformed deformed state
B. Mechanical analysis
Forces applied
Processes at grain scale that allow structures to develop
Compression (stress) [ Contraction/Shortening (strain)
Change in Length (thickening)
Folds (Macroscale)
Features that can be traced over a region encompassing several
outcrops to whole mountain ranges
Folds (Mesoscale)
Features visible in rock outcrops but cannot necessarily be traced from outcrop
to outcrop
Folds (Microscale)
Faults (Macroscale)
Faults (Mesoscale)
Faults (Microscale)
Mechanics of Structures
How Rocks Deform Depend on:
Temperature
Pressure (rock or lithostatic pressure)
Pore fluid pressure
Composition of rocks (e.g. quartzite vs. limestone)
Force applied
Rate of deformation
Forces: Push or Pull.
Vector quantity (SI Unit = Newton = kgm/s2)
Body force
Surface force
Body Force: They act on each particle of rock in a
volume, and its magnitude is proportional to the mass
within that volume.
Gravitational Forces Electromagnetic Forces
Surface Force: Forces that result from the action of one
body / part of a body on another across a shared surface. They
act on a specific surface of a body.
Traction: Intensity of Force
= F/A
But
Traction at a point,
= dF/dA
Magnitude & direction of traction can vary from point to point across a
surface.
Force Traction
(-ve)
(+ve)
Surface Stress
Opposing Forces (pairs of equal & opposite traction
acting on any surface of specific
orientation)
Course Outline
Introduction to Geometric Analysis Module 1
Strain
Stress Module 2
Rheology
Failure Criteria
Manifestation of Deformation in rocks & their tectonic associations
Faults
Geometry, Classification
Folds Module 3
Geometry
Orientation
Classification
Introduction to Mechanics of Folding & Faulting Module 4
Course Outline
Textbooks:
Earth Structure: Van der Pluijm & Marshak
Structural Geology : Twiss & Moores
Structural Geology : Fossen
Basic Methods of Structural Geology: Marshak & Mitra
Structural Geology: Billings
Grading
Class tests & Quiz
Assignments
Participation in Class
Office : Room # A18, Prefab 1
Email address: kathakali@iiserkol.ac.in
