Geology Department

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Geology 110 Syllabus

NORMAL FAULTS

Reverse/Thrust FaultsStrike Slip/Transform/ Wrench

I. NORMAL FAULTS - extend and thin the crust

A. Generally high-angle faults (~60o) but, in the 1980's recognized low-angle normal faults

B. Emplace younger rocks upon older ones

C. Excise units

D. Result in basin (down dropped blocks = graben) and ranges (uplifted = horst)

e.g., Basin and Range Province in western U.S., Cordillera (metasediment horst -Tertiary infill with sediments = basins)

II. TODAY RECOGNIZE FORMATION OF HALF GRABENS:

A. Syn-sedimentary/deformation deposit

1. Thickens on hanging wall, causes roll over anticline

a. Causes antithetic fracture

B. Extension: local scale

1. Elastic bending (e.g., rubber eraser)

a. Above footwall ramp

2. Indentation from beneath - (plutons, diapier)

3. Collapse features - (calderas)

C. Extension: regional (continent/ocean) scale

1. Mid-ocean ridge:

2. Continental extension:

a. Classical typography = horst/ graben

b. Today half-grabens

e.g., western Cordillera

3. Tertiary sediments = Tertiary intrusions

(Coney, P., 1980, GSA Memoir 153, p. 7-31, 1st to describe metamorphic core complexes)

(Wernicke, B., Nature, v.291, p. 645-48, 1981 - metamorphic core complexes)

4. Structurally, how is continental extension accommodated?

a. Faults and or ductile shear zones extend down through the crust

b. Igneous intrusions fill in dilation spaces

c. Penetrative ductile stretching - lower part of crust stretches like taffy