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

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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).

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slide9

AnnouncementsMidterm Monday!Bring calculator, protractor, ruler, stereonet and tracing paperTalk 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)

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

1. Descriptive terminology2. Determining direction of slip3. Determine sense-of-shear

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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)

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

concept of fault zone

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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"

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Determining kinematics from fault fabrics1st step: figure out direction of slip2nd step: figure out sense-of-shear- this requires looking at fabrics that are oriented perpendicular to slip direction

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

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onto sense-of-shear...

chatter marks: step-like features oriented perpendicular to striations

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What is it?

top-to-the right

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

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conjugate Riedel shears

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

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What is it?

R\'

R\'

R

R

main fault

left lateral

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

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A summary What is it?

breccia

cataclasite

Riedel shears

gash fractures: form perpendicular to s3

normal fault

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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

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