today’s lecture - glg310--structural...

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GLG310 Structural Geology


Today’s lecture

• Let’s see some Geologic Structures!

– Grand Canyon and geologic time

– Primary versus secondary structures

• Introductory concepts

– Deformation

– Descriptive analysis

– Kinematic analysis

– Dynamic or mechanical analysis

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26 August 2004 GLG310 Structural Geology

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26 August 2004 GLG310 Structural Geology Dallas D. Rhodes, 2004


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26 August 2004 GLG310 Structural Geology Leslie, 2004

26 August 2004 GLG310 Structural Geology Leslie, 2004

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http://jan.ucc.nau.edu/rcb7/Grand_Canyon_Pz.jpg

26 August 2004 GLG310 Structural Geology Keller, 2002

http://jan.ucc.nau.edu/rcb7/Grand_Canyon_Pz.jpg

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26 August 2004 GLG310 Structural Geology Burger Structural Geology slide set


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Burger Structural Geology slide set

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The Fundamental

Structures • Contacts: Depositional,

unconformities, intrusive, fault, shear zones

• Primary structures: Those that develop during the formation of a rock body

– In magma/lava before it becomes intrusive/volcanic rock

• Vesicles, flow banding, etc.

– In seds before they become sed rox • Cross beds, ripple marks, etc.

– In metamorphic rocks most of these are secondary


• Secondary structures: (focus of our course)

– Form in sedimentary or igneous rocks after lithification or in metamorphic rocks during or after their formation

– Joints and shear fractures

– Faults

– Folds

– Cleavage, foliation, lineation (penetrative)

– Shear zones

The Fundamental

Structures

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Important terms

• Deformation: change in shape from some

initial (undeformed) to a subsequent

(deformed) configuration

• Qualitative terms describing deformation

– Brittle: Discrete failure accommodates

deformation; formation of faults and fractures

– Ductile: Distributed failure, usually by flow


Structural Analysis

• Descriptive Analysis

– Recognize and describe structures and measure their locations, geometries and orientations

• Scale, Structural Elements

• Kinematic Analysis

– Focus on motion of materials

• Dynamic Analysis

– Interpret motions in terms of applied forces

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Observations must match

scale of problem


Structural elements

Dal

las

D. R

hodes

, 2004

Physical and geometric,

importance of what is there and

not there, real and imaginary

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Fold structural elements (idealizations)

Structural elements

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Structural elements

The structure of this part of the Canadian Cordillera is dominated by thrust faults which are

generally southwest-dipping and concave upward in profile. The faults flatten with depth

and have the upper side displaced relatively north-eastward and upward. They gradually cut

up through the stratigraphic layering northeastward, but commonly follow the layering over

large areas… Many of the faults bifurcate upwards into numerous splays, and the total

displacement along them becomes distributed among these splays. Folds are widespread and

have developed in conjunction with the thrusting… Many of the thrust faults themselves are

folded along with the sedimentary layering… The folds generally are inclined to the

northeast or are upright. Many of the thrusts die out as folds. (Davis, et al., 2012, p. 30)


Kinematics (Slip, flow)

http://sps.unavco.org/crustal_motion/dxdt/

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Deformation types


Returning to scale

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Dynamic models


Dynamic models Descriptive

Kinematic

Model (uncertain!)

“My working model is that the manufacturer, after preparing the pizzas, chose

not to stack the boxed pizzas horizontally in freezer compartments. The

manufacturer may have concluded, perhaps on the basis of experimentation, that

tall stacking of pizza-filled boxes might have the adverse affect of flattening

cardboard to cheese and tomato sauce before freezing set in. Instead, the pizzas

may have been filed vertically. If moist, the pepperoni, under the influence of

gravitational forces, might have been vulnerable to translation along the low-

viscosity tomato sauce discontinuity. Each of the pepperoni rounds would have

cease moving when it encountered the frictional resistance of another one. What

was not clear to me then, nor is it now, is the rate at which the pepperoni

moved—was it rapid or sluggish? The magnitude of the stresses required to

initiate movement is also a puzzle. In fact, interpreting the strength of the

various materials as a function of temperature would constitute a major study in

itself. (Davis, et al., 2012, page 9)

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Dynamic models

Physical

Models

(“sandbox”,

“analog

models”)

http://www.swri.edu/4org/d20/gg/analog/default.htm


Dynamic models 1992 Landers, CA earthquake

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Dynamic models Mathematical

models

(engineering-

type tools)


Today’s lecture

• Let’s see some Geologic Structures!

– Primary versus secondary structures

• Introductory concepts

– Deformation

– Descriptive analysis

– Kinematic analysis

– Dynamic or mechanical analysis

today’s lecture - glg310--structural...

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