Society of Earth Science Students A student-run club for all students interested in Earth Science, regardless of major. Activities: field trips, weekly speakers, outreach to kids and adults, and the Tucson Gem and Mineral Show Junior Education area Meetings: Fridays 1:00 pm Gould-Simpson Building Room 209

Society of Earth Science Students Meetings: Fridays 1:00 pm Gould-Simpson Building Room 209 Some past trips: Pinacate volcanic field, Mexico Grand Canyon Kartchner Caverns Moonlight hikes

Society of Earth Science Students Meetings: Fridays 1:00 pm Gould-Simpson Building Room 209 Tucson Gem and Mineral Show

Society of Earth Science Students Meetings: Fridays 1:00 pm Gould-Simpson Building Room 209 Come to the meetings Join the field trips Free pizza and soda at the first meeting! Friday September 6 th

(Chapter 1 in D & R) Overview of Structural Geology

OUTLINE  1) What is structural geology?  2) What are structures?  3) Goals of structural analysis  4) Intro. Geometry

What is structural geology? - Study of rock deformation, “the study of the architecture of the Earth’s crust” - “forensic science”

Why is structural geology important? - Fundamental to Earth Science - Insight about planetary evolution - Relations between tectonics and climate - Natural hazards - Resource exploration and management

What skills will be practiced? - Scientific method - 3-D Visualization and presentation - Mapping - Quantitative - Integrating multiple disciplines

What are structures? Two main types: (1)Primary structures: Develop during formation of a rock body; e.g., cross-bedding, ripple marks, mudcracks, pillows (in basalt) (2) Secondary structures: Form in rocks as a result of deformation- the structures this class are focused on!

Secondary Structures Devil’s Postpile, Sierra Nevada, CA Joints: fractures with very little or no displacement Veins: fractures filled with minerals

Secondary Structures cont. Faults: fractures that have accommodated displacement Folds: systematically curved layers

Secondary Structures cont. Cleavage: closely spaced subparallel surfaces that impart a splitting property Foliation: very closely spaced subparallel planar features

Secondary Structures cont. Lineations: elongate linear features Shear zones: “faults with widths”

Secondary Structures cont. “ Microstructures ”

Goals of Structural Analysis  Geometry: mapping, measurements  Kinematics: movements related to deformation –Translation: change in position –Rotation: change in orientation –Distortion: change in shape –Dilation: change in volume Dynamics/Mechanics: relating deformation to stresses

What is it??

What is it?? (interpretation) Marker bed faults drag folds joints

Intro. Geometry: Structural measurements Tools: compass and protractor  Planar structures  Strike: compass direction of trace of horizontal line on a plane; bearing (quadrant, E or W of north) or azimuth (degrees clockwise from N)  Dip: inclination of plane from horizontal, perpendicular to strike

Linear structures  Trend: direction of a vertical plane that contains the linear feature in the direction of plunge.  Plunge: angle between line and horizontal

Next Lecture: Geometry and kinematics of large-scale deformation- Plate Tectonics Read Chapter 10 in Davis and Reynolds

Important terminology/concepts - Structural geology- what is it and why is it important? - Primary structures vs. Secondary structures - Joints - Veins - Faults - Folds - Cleavage - Foliation - Shear zones - Lineations - Structural analysis - Planar features: strike and dip - Linear features: trend and plunge