Download lecture1 - Geological Sciences

GEOL 360, Structual Geology
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Class information & syllabus
Laboratory & class materials
Stereonet exercises
Problem sets
Exam review
Meeting: G360 meets MWF 11:00-11:50, Lind 103
Laboratory, Wednesday at 2:00 pm, Lind 103
Text: Structural Geology of Rocks and Regions, Davis and Reynolds, 1996
Supplemental Text: Geology in the Field, Compton, 1985.
Instructor: Dr. Charles Rubin, [email protected].
Office: Hebeler 109
Telephone: 963-2827
Office hours: My office door is usually open or by appointment
Teaching Assistant: Josh Dailey
Office: Bouillon, Rm 120
Telephone: 963-2707
Why is it important?
Fundamental discipline in Earth
Sciences- “the study of the
architecture of the Earth’s crust”
Geometry is key to many ES
applications (oil, mining,
earthquake hazards, slope
stability);
Our goals:
(1) to learn how to make structural
observations & present them to
others;
(2) to interpret the processes that
led to the “final
product”- the geologic observations.
Student learning objectives:
Develop an understanding of (1) the scientific method, (2) rock deformation,
rock failure, strain and stress, (3) types of faults and folds, kinematic
analysis, stereographic analysis of faults and folds, (4) construction and
interpretation of geologic cross-sections.
Problem sets: There will weekly assignments during the quarter. Late
assignments will be deducted 10% per day that they are late.
Laboratory assignments: Many of the laboratory assignments for this
course require a lot of thinking as well as some repetitive, time-consuming
work. Please do not wait unit the day before the assignments are due to
begin working on them.
Problem sets: There will weekly assignments during the quarter.
Exams will be graded by Charlie Rubin. We do not accept a late
assignment after we have returned the graded exercise to the rest of the
class.
Some tips for a successful quarter:
(1) Do not miss a class, not one. Reading your text is not a
substitute for attending lecture.
(2) Read your text assignments before class ask questions
and participate in class.
(3) Take good, complete notes. The more you write, the better.
If you do not understand a concept or example, ASK. If I
go too quickly, ask me to repeat the information.
(2) If you do not understand a concept that I discuss in class,
ask questions during class or come and see me. The only
way I can help you understand the material is if you ASK
for help!
Some tips for a successful quarter:
It is to your advantage to study and work with other students in
this course. Discuss your laboratory exercises and data, its
analysis and interpretations with others members of the class;
this is a constructive and realistic way of solving geologic
problems.
However, your final product should be your own individual and
creative work. If you have any questions about the
acceptability of collaboration, ask Charlie Rubin before you
complete the assignment, not after.
Remember, few aspects of geology are completely cut and dry,
your laboratory exercises are not exception to this. Don't
forget scientific writing style, logic, organization, data quality,
and presentation are all part of the final product.
- ME  I’m an professor of Geological Sciences and teach a
mix of undergraduate and graduate classes, which I
enjoy doing
 I teach GEOL 360. I also teach other courses such as
G101 (intro geology), G170 (EQ’s and volcanoes),
G415/515 (earthquake geology), G410 (physics of
avalanches), and G210 (field geology), and seminars on
the active tectonics of mountain belts.
GEOL 360 addresses the
architecture of the Earth the physical components
or structures that make
up the Earth’s crust, and
that form in response to
applied forces and
stresses.
What is structural geology – study of deformed rocks,
sediments, and landforms
 necessary to define geometries of land forms and rocks in 3D
Observations
direct: mapping, drill holes, laboratory, experimental
indirect: seismic, gravity, magnetics, etc.
What do we do?
 measure or infer translation, rotation and strain
(deformation history): KINEMATICS
 related to engineering mechanics and material science,
but, we almost always only have the end-product
 engineers want to know effect of stress on an object
 geologists try to infer stress from deformed object;
much more difficult: MECHANICS & DYNAMICS
GOALS FOR Geol 360
We have these goals:
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Critical thinking & the scientific method
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Analytical methods to decipher earth processes
Scientific principles that govern Solid-Earth
processes
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Observational techniques & reasoning processes
GOALS FOR Geol 360
Comfort with new language
 lots of new terminology throughout the course.
 use the book’s glossary for quickie refresher
GOALS FOR Geol 360
Present lecture material that accounts for
different learn styles:
 seeing/visual
 reading
 hearing
 personal discovery
Deformation - used in several
ways:
1) Structural changes in location,
orientation, shape, and volume of a
body of rock.
2) Physical and chemical processes
that cause the changes.
3) Geologic structures that form to
accommodate the changes.
Space Shuttle view of the Greater
Himalayas
Any body of sediment/rock,
regardless of strength will deform if
conditions are right.
Deformation of the Earth’s Crust
 Deformation results from stresses that exceed a rocks strength.
When peak strength is reached, failure is either brittle (fracture) or ductile
(flow), depending on how the physical environment has affected rock
strength (e.g., temperature, strain rate, etc.).
Stresses are applied to rocks in countless ways: burial, cooling/heating,
intrusion, plate motion, impacts from space.
The structural geologist is faced with a finished product and has the
inverse task of learning how it came to be - effectively the opposite task
that faces an architect.
What is the structure? What were the starting materials? What’s the
geometry? How did it change shape? Source of stresses? Sequence of
deformation?
Deformed fossils (trilobites), showing strain
Deformation is the result of plate tectonics and is observable.
Plate motions are responsible for many of the stresses that cause
deformation of rock.
Distortions of the Earth’s crust are most prominent at plate margins; the
location of much of the Earth’s high mountains.
engineering:
apply stress
observe what happens
structural geology:
?
infer what happened
and original shape
observe deformed object
to describe deformation, one needs a reference frame,
typically the reference frame is the “undeformed state”
modified from Allmendinger: http://www.geo.cornell.edu/geology/classes/RWA/GS_326/GEOL326.html#aa40
Fundamental
Structures
• Contacts
The most basic structures,
they separate one rock unit
from another:
Depositional
Unconformities
Faults
Intrusive
Shear zones
Fundamental Structures
Primary Structures: These are primary sedimentary
structures. They are useful as strain markers (giving us an
initial state) and as stratigraphic facing indicators.
• Do not confuse primary sedimentary structures with
secondary structures, which are the result of deformation.
up
Bedding Laminations
Graded Bedding
Cross-Beds (asymmetric)
up
Oscillation Ripples (symmetric)
up
Mud Cracks
up
Rain Drops / Footprints
up
Load Casts
up
Tool Marks
up
Root Casts / Worm Burrows
up
Stromatolites
up
Primary vs. secondary structures.
Primary: depositional contacts, cross-bedding, ripple marks,
Ropy textures in lavas, mud-cracks;
Geologic structure at different scales:
regional (Landsat TM)
global (Topex/Poseidon)
from: http://topex.ucsd.edu/marine_grav/explore_grav.html
Macroscopic (map scale)
Keystone thrust
(dark over light)
Calico folds
both from: Robert Varga, http://www.wooster.edu/geology/GEO313/Images/
Mesoscopic
(outcrop)
all from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/
Mesoscopic
(hand sample)
sigmoidal structures
(shear zones)
from: Keck geology slide set, Paul Karabinos
site: http://www.science.ubc.ca/~eoswr/slidesets/keck/
folds in gypsum
from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/folds2.html
Microscopic:
s-c fabric
from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/
Dynamic recrystallization
(formation of s-c fabric)
from Allmendinger: http://www.geo.cornell.edu/geology/classes/RWA/GS_326/GEOL326.html#aa40
Microscopic and mesoscopic:
vein
image from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/
animation from Allmendinger: http://www.geo.cornell.edu/geology/classes/RWA/GS_326/GEOL326.html#aa40
Scale of analysis.
“Tools” for interpretation
Original horizontality (Nicholas Steno)
Layers that are tilted were deposited horizontally
Fundamental concept that gave birth to structural geology
from Stephen J. Reynolds, (http://www-glg.la.asu.edu/~sreynolds/geologic_scenery/geologic_scenery_images.html
Importance of strike and dip to describe geometry
2 perpendicular lines that together define the plane
N
tilted layer
strike
b
horizontal plane
b= strike angle
inclined plane
strike measured relative to north
in horizontal plane
dip
strike in and out of plane of page

= dip angle
strike
vertical layers
dip measured relative to horizontal
along line of strike
dip
dip
Superposition of strata:
in a sequence of undeformed rocks……
oldest rocks are on the bottom with
progressively younger rocks found at
higher stratigraphic positions
Stratigraphic “facing” is an important tool for structural
geology
are the layers right side up or upside down?
upside down implies deformation
time 1
time 3
time 2
time 4
from Stephen J. Reynolds, (http://www-glg.la.asu.edu/~sreynolds/geologic_scenery/geologic_scenery_images.html
Cross-cutting relationships
where geologic features intersect, the feature doing
the “cutting” is the youngest feature
unconformity
cuts down into
strata below
Grand Canyon Great Unconformity