GEOL 360, Structual Geology

www.geology.cwu.edu/blue.hmtlenter g360 in left navbar search and hit enter, this

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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 103Laboratory, 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, charlier@geology.cwu.edu.

Office: Hebeler 109Telephone: 963-2827Office hours: My office door is usually open or by appointment

Teaching Assistant: Josh DaileyOffice: Bouillon, Rm 120Telephone: 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 setsProblem sets: There will weekly assignments during the quarter. Late : There will weekly assignments during the quarter. Late assignments will be deducted 10% per day that they are late. assignments will be deducted 10% per day that they are late.

Laboratory assignmentsLaboratory assignments: Many of the laboratory assignments for this : Many of the laboratory assignments for this course require a lot of thinking as well as some repetitive, time-consuming 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 work. Please do not wait unit the day before the assignments are due to begin working on them. begin working on them.

Problem setsProblem sets:: There will weekly assignments during the quarter.There will weekly assignments during the quarter.

ExamsExams will be graded by Charlie Rubin. We do not accept a late 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 assignment after we have returned the graded exercise to the rest of the class.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.

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.

- ME -

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

Observationsdirect: mapping, drill holes, laboratory, experimentalindirect: 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

Critical thinking & the scientific method

Analytical methods to decipher earth processes

Scientific principles that govern Solid-Earth processes

Observational techniques & reasoning processes

We have these goals:

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Comfort with new language

lots of new terminology throughout the course.

use the book’s glossary for quickie refresher

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Present lecture material that accounts fordifferent learn styles:

seeing/visual

reading

hearing

personal discovery

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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.

Any body of sediment/rock, regardless of strength will deform if conditions are right.Space Shuttle view of the Greater

Himalayas

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?

Deformation of the Earth’s Crust

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:

?structural geology:

apply stress observe what happens

observe deformed objectinfer what happened and original shape

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

• ContactsThe 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 LaminationsGraded Bedding

Cross-Beds (asymmetric)

Oscillation Ripples (symmetric)

up

up

up

up

Mud Cracks

Rain Drops / Footprints

Load Casts

Tool Marks

up

up

Root Casts / Worm Burrows

Stromatolites

up

up

Primary vs. secondary structures.

Primary: depositional contacts, cross-bedding, ripple marks, Ropy textures in lavas, mud-cracks;

Geologic structure at different scales:

global (Topex/Poseidon)

regional (Landsat TM)

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)

folds in gypsum

from: Keck geology slide set, Paul Karabinossite: http://www.science.ubc.ca/~eoswr/slidesets/keck/

from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/folds2.html

Microscopic:

s-c fabric

Dynamic recrystallization (formation of s-c fabric)

from Allmendinger: http://www.geo.cornell.edu/geology/classes/RWA/GS_326/GEOL326.html#aa40

from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/

Microscopic and mesoscopic:

vein

animation from Allmendinger: http://www.geo.cornell.edu/geology/classes/RWA/GS_326/GEOL326.html#aa40

image from: J. Waldron, http://www.stmarys.ca/academic/science/geology/structural/

Scale of analysis.

“Tools” for interpretation

Original horizontality (Nicholas Steno)Layers that are tilted were deposited horizontallyFundamental 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 geometry2 perpendicular lines that together define the plane

strike

dip

horizontal plane

inclined plane

strike in and out of plane of page

dip

vertical layers

strike

dip

strike measured relative to northin horizontal plane

dip measured relative to horizontalalong line of strike

= dip angle

N

= strike angle

tilted layer

Superposition of strata:

in a sequence of undeformed rocks……oldest rocks are on the bottom with

progressively younger rocks found athigher 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 2

time 3 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