Lecture 1 Introduction Nature of Structural Geology Study of Deformation What was the rock like before deformation What forces were required to deform the rock How long and in what order did deformation events proceed ID: 931685
Download Presentation The PPT/PDF document "GY403 Structural Geology" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
GY403 Structural Geology
Lecture 1: Introduction
Slide2Nature of Structural Geology
Study of
Deformation
What was the rock like before deformation?
What forces were required to deform the rock?
How long and in what order did deformation events proceed?
How does the deformation relate to global tectonics?
Deformation: change in
position, shape
and/or volume in a rock mass.
Strain
is synonymous with deformation.
Slide3Plate Tectonics & Structural Geology
Orogenic Belts: produced along a convergent plate boundary.
Orogenic belts are the focus of structural geology because they record long periods of multiple deformation events.
The strain in orogenic belts is primarily an effect of
distortion
(i.e. change in shape) as opposed to
dilation
(i.e. change in volume
).
Slide4Fundamental Structures
Contacts
: boundaries that separate one rock body from another.
Primary Structures
: structures that are produced during formation of rock body.
Depositional
contact.
Unconformable contact.Cross bedding.Vesicles in basalt.
Slide5Fundamental Structures cont.
Secondary structures
: structures produced after the rock body that they affect.
Fault
contacts.
Folds.
Joints
and shear fractures.
Tectonite fabric
(cleavage, foliation and/or lineation
).
Slide6Faults
Fault
: a fracture displaying significant apparent offset of
structures.
Cataclasite
: fragmented rock produced by the grinding action of a fault at low pressure (minimal depth)
activity.
Mylonite: recrystallized rock generated by deep (high pressure) fault motion.Ductile Shear Zones: fault zone rocks that contain
mylonites
that deform in a ductile
manner.
Slide7Faults cont.
Measurable offsets are present along faulted
contacts.
Slide8Folds
Folds
: formed when beds or fabric are deformed into curved or bent geometries on virtually any scale.
Fold Mechanisms:
Compression due to tectonic
forces.
Drag folding in fault
zones.Syn-depositional slumping.Intrusion of magma or other viscous materials.
Mass
wasting.
Slide9Folds cont.
Folds are documented by measurement of hinge and axial trace attitude, wavelength
distance.
Hinge line
(trend & plunge)
Axial trace
(strike)
Interlimb
angle
Fold limbs
(strike & dip)
wavelength
Slide10Joints & Shear Fractures
Joint: a fracture where there has been no apparent slippage (i.e. no offset is apparent
).
Shear fracture: a fracture that displays a small amount (< cm) of apparent
offset.
Note: before designating a shear fracture make sure to investigate all 3D possibilities for
slip.
Slide11Joint Fractures cont.
Produced by expansion during erosional unloading
Slide12Tectonite Fabric
Tectonite
Fabric: a
cleavage
,
foliation
and/or
lineation that is pervasive in a rock mass.Tectonite fabrics are produced by the directed stress set up by plate tectonics, and are usually found in regional metamorphic rocks.
Slide13Cleavage
Slaty
cleavage axial planar to
fold.
Cleavage forms
synchronously.
with folding if its parallel to axial
plane.
Axial Plane
Slaty
Cleavage
Slide14Foliation
Foliation: preferred alignment of mineral grains, or layer bands that are produced by metamorphic
recrystallization.
Foliation
Slide15Stretch-Pebble Metaconglomerate
Alignment of stretched pebbles in
metaconglomerate.
Long axis of stretched pebble was perpendicular to maximum compressive
stress.
Slide16Concept of Detailed Structural Analysis
Descriptive Analysis
: recognizing and describing structures and measuring their locations, geometries, and orientations.
Kinematic Analysis
: interpretation of the deformational movements in a rock mass necessary to produce deformational structures.
Translation
(described by a linear vector
).Rotation (described by axis, amount and sense of rotation).
Dilation
(Volume change; +
V= volume gain
).
Distortion
(change in shape
).
Dynamic (Force) Analysis: role of forces driving
deformation.
Tectonic Analysis: developing tectonic models for the evolution of the Earth over
time.
Slide17Kinematic Analysis Components
Rigid
Body:
Translation (Vector
).
Rotation (Axis, Amount & Sense of Rotation
).
Non-Rigid Body:Dilation (Volume).
Distortion (
Shape
).
Slide18Scale
Structural classification systems are dependent on scale of observation- a structure that appears ductile may be brittle at a larger scale.
Slide19GSA Geological Time Scale (2009)
Slide20Geologic Time Scale Summary
Eons: Hadean (4.56-3.95Ga), Archean (3.95-2.5Ga), Proterozoic (2.5Ga-542Ma), Phanerozoic (542Ma-present
).
Eras: Paleozoic (542-251Ma), Mesozoic (251-65.5Ma), Cenozoic (65.5Ma-present
).
Periods: Cambrian(542Ma), Ordovician (488Ma), Silurian(439Ma), Devonian(416Ma), Mississippian(359Ma), Pennsylvanian(318Ma), Permian(299Ma), Triassic(251Ma), Jurassic(201.6Ma), Cretaceous(145.5Ma), Tertiary(65.5Ma), Quaternary(2.6Ma
).
Slide21Summary of Items to Know for Exams
Geologic Time Scale (Eons, Eras, Periods and boundary dates
).
Components of Structural
Analysis:
Descriptive, Kinematic, Dynamic,
Tectonics.
Examples of each.Components of Kinematic Analysis:Translation, Rotation, Dilation,
Distortion.
Geological examples of
Each.
Rigid Body vs. Non-Rigid Body
deformation.
Fundamental Structures (know examples
):
Primary
structures.
Secondary
structures.