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Lecture

EARTHSC 1G03 Lecture Notes - Compressive Stress, Syncline, Lithification


Department
Earth Sciences
Course Code
EARTHSC 1G03
Professor
Maureen Padden

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CHAPTER 11 - GEOLOGIC STRUCTURES
CAUSES OF ROCK BREAKAGE AND BENDING
Stress and Strain in Lithosphere:
Tectonic forces cause rock deformation causing change in orientation, location, and shape.
Stress is measurable force per unit area at a point
Strain is change in size (volume) and/or shape
Forces:
Compressive
Pushed in f/ opp. Sides
- Causes shortening
Tensional
Pulled f/ opp. Sides
- Causes stretching or breaking
Shear
Convergent zones
Divergent zones
Tranform zones
Rocks Response:
Elastic: deformed material recovers original shape after stress is reduced/removed
o Elastic limit: the limit to which rock can bend before damage is permanent
Ductile (plastic): bends under stress and remains as such
o Permanent damage due to folding or bending of rock layers
o Folds: permanent wavelike deformations in layered rocks
High temperatures and pressures
Brittle: rock breaks under stresses
o Result in faults or joints; fault: fracture in bedrock along which rocks on one side
move/displace relative to the other side
Joint (or joint sets): fracture/crack in bed rock w/o displacement
o Compressive forces cause: reverse faulting
o Tensional forces cause: faulting
o Shear forces cause: strike-slip faulting
Rocks response influenced by: stress type, rock type, temperature, pressure, fluids, length and
magnitude of stress applied.
MEASURING AND RECORDING GEOLOGIC STRUCTURES
GEOLOGIC MAPS
Uses standardized symbols and patterns to represent rock types and geologic structures
Geologic maps show the type and distribution of rock types, structural features, ore
deposits, etc.
Data obtained either from ground or from remotely sensed data f/ a satellite or airplane
STRIKE AND DIP
Sedimentary beds can be deposited as horizontal beds or strata
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