Announcements

Midterm Monday!

Bring calculator, protractor, ruler, stereonet and tracing paper

Talk This Thurs. 4 pm, Rm. Haury Bldg. Rm 216, "The role of orogen-parallel extension during the India-Asia collision", write

1 paragraph summary (+1% extra credit)

Brittle fault rocks and kinematic indicators(D&R: 280-286; 297-300)

1. Descriptive terminology

2. Determining direction of slip

3. Determine sense-of-shear

Breccias: fault rocks composed of angular fragments of wall rock set in a finer-grained matrix of crushed wall rock; classified based on clast size

megabreccia! (well, almost)

breccia

gouge: very fine-grained; clayey

cataclasite: very fine-grained strongly indurated fault rock (white in photo)

concept of fault zone

cataclasite: commonly forms "ledges"

pseudotachylite: dark, very fine-grained and generally glassy fault rock; thought to represent rapidly chilled rock melt, with melting of rock due to shear heating during an earthquake event- WOW!

the glassy surface is the "generation" surface and the black veins are "injection veins"

Determining kinematics from fault fabrics

1st step: figure out direction of slip2nd step: figure out sense-of-shear- this requires

looking at fabrics that are oriented perpendicular to slip direction

slickensides: polished shiny fault surfaces due to abrasive actionslickenlines/striations: scratches

Grooves

Larger Grooves

chatter marks: step-like features oriented perpendicular to striations

onto sense-of-shear...

Crystal fiber lineations: produced by preferred directional growth of minerals during faulting in direction of movement

What is it?

top-to-the right

Drag folds

conjugate Riedel shears

R: synthetic Riedel shearR': antithetic Riedel shearP: synthetic shear, subordinate to R and R' or absent

R

What is it?

main fault

Where are R and R' shears?What is the sense-of-shear?Explain why R' shears are associated with veins

R

R'

R'

left lateral

photo courtesy of Brent Morris

A summary What is it?

gash fractures: form perpendicular to 3

cataclasite

breccia

normal fault

Riedel shears

Important terminology/concepts

Breccias

megabreccia

breccia

gouge

cataclasite

fault zone

pseudotachylite

slickensides

slickenlines/striations

grooves

chatter marks

crystal fiber lineations

drag folds

Riedel shears

gash fractures