Announcements 1.Reminder, this Saturday field trip. Meeting place/time: GS loading dock at 7:45 am. Bring hiking gear, lunches, water. 2.Extra credit: get 1 point (test-equivalent; for each tectonics -related Geoscience colloquium attended between now and end of class). A list of colloquiums to attend will be posted on the web. Turn in a paragraph summarizing the main points of the talk.

Normal faults -rifted continental margins -form in extension -typical for continental and oceanic lithosphere -jargon (horsts, grabens, listric, detachment) -are they low-angle? -core complexes -Example: Basin and Range, -the way we think it works, mechanically - Normal fault systems (D&R: )

Can you spot the fault?

It’s low angle, but so are thrust faults: KEY: puts young (hanging wall) on old (footwall). The fault markers (slickenlines Etc) are the same.

Horsts and grabens Iin agreement with Coulombian mechanics

Some problems with the model- Most faults look listric and low angle Listric

Pure shear or simple shear??

Simple shear A complication of simple shear

How do extensional faults look like?

Sedimentation takes place during faulting; Also block rotation domino-style

Cottonwood Canyon - this Saturday’s trip

Figuring out timing of extension: 1. Magmatism 2. Sedimentation

High angle faults are present too- East African rift large scale example Moab fault

Basin and Range- world’s most studied extensional province-low-angle normal faulting prevails.

How do continents break apart?

A view of the Mountains north of us… the Catalinas

Core complexes- metamorphic core

Exhumation of metamorphic cores beneath detachment faults Extension of the upper crust commonly requires flow in the mid- to low crust and/or magmatic additions

Important things about normal faults. 1. Fundamental to structure of continents and oceans.

Important things about normal faults. 2. Two different styles: the low-angle and high-angle.

Important things about normal faults. 3. Can take up as much extension as compressional orogens shorten.

Important things about normal faults. 4. You live in the most famous (and perhaps most important extensional region-the B&R).

Important things about normal faults. 5. Extension is accompanied by big-time sedimentation-important for oil formation.

Important things about normal faults. 1. Fundamental to structure of continents and oceans. 2. Two different styles: the low-angle and high-angle. 3. Can take up as much extension as compressional orogens shorten. 4. You live in the most famous (and perhaps most important extensional region in the world-the B&R). 5. Extension is accompanied by big-time sedimentation-important for oil formation.