Lecture 01 Introduction S05
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Transcript of Lecture 01 Introduction S05
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Structural Geology
GLY 4400 Lecture 1
Introduction
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What is Structural Geology?
Structural Geology is the branch of geologythat deals with the form, arrangement, and
internal structure of the rocks, andespecially with the description,representation, and analysis of structures,chiefly on a moderate to small scale
Similar to tectonics, but the latter term isused for broader regional or historicalstructures
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Geologic Structure
A geometric feature in rock whose shape,
form, and distribution can be described
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Geometrical Classification
A. Planar to subplanar
B. Curviplanar
C. Linear
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Geological Significance
Classification A. Primary - Formed by the formation of the rock itself
B. Local gravity-driven - formed due to slip down aninclined surface - Includes: Slumping, at any scale, driven
by gravitational potential which exceeds friction
C. Local density-inversion driven - formed because of locallateral rock-density variations, causing local buoyancyforces
D. Fluid-driven pressure: Injection of unconsolidatedmaterial due to sudden release of pressure
E. Tectonic - Formed due to interactions betweenlithospheric plates, or regional interactions between theasthenosphere and the lithosphere. The forces aregravitational, trying to achieve isostatic equilibrium, atcrustal to lithospheric scales
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Time of Formation Classification
A. Syn-formational - Structure forms at the same
time as the material that forms the rock
B. Penecontemporaneous - Formed afterdeposition, but before full lithification
C. Post-formational - Structure forms after the
rock has fully formed, as a consequence of forces
not related to the formation of the rock
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Debris Flow
Flowing mixture is dominantly sediment
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Formation Process Classification
A. Fracturing - related to development orcoalescence of fractures in rock
B. Frictional sliding - The slippage of one rock
past another, or of grains past each other, resistedby frictional forces
C. Plasticity - Deformation by the internal flow ofcrystals w/o loss of cohesion, or non-frictional
sliding of crystals past each other D. Diffusion - material transport either in the
solid-state or by dissolution in a fluid
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Mesoscopic Cohesion Classification
A. Brittle - loss of cohesion across a
mesoscopically discrete surface
B. Ductile - w/o loss of cohesion across a
mesoscopically discrete surface
C. Brittle/ductile - some combination of the
two behaviors
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Significance of Strain Classification
A. Contractional - Shortening of a region
B. Extensional - Lengthening (extension) of
a region
C. Strike-slip - movement w/o dimensional
change
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Distribution of Deformation
Classification A. Continuous - deformation throughout the rock
body, on all scales
B. Penetrative - At the scale of observation, occurs
throughout the rock body - at finer scales, theremay be gaps between structures
C. Localized - Continuous or penetrativethroughout a definable subregion of the overall
structure D. Discrete - a structure which occurs as an
isolated feature
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Plate Tectonic Features
Figure 1.4 in text