Part I: Rheology & Dynamics ToDo 3: 0D shear 1. Stress, strain, - - PowerPoint PPT Presentation

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Sep 20, 2022 16 likes •238 views

Part I: Deformation mechanisms 1.What is high temperature? (3-11) 2. Diffusion Creep (3-23) ToDo 1: flow laws 3. Dislocation Creep (3-25) ToDo 2: Mechanism 4. Rocks: multi-scale materials (3-30) Maps Part I: Rheology & Dynamics

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Part I: Deformation mechanisms 1.What is “high temperature”? (3-11)

2. Diffusion Creep (3-23)
3. Dislocation Creep (3-25)
4. Rocks: multi-scale materials (3-30)

Part I: Rheology & Dynamics

1. Stress, strain, forms of suffering (4-1)
2. Viscoelasticity, Thermodynamics (4-6)
3. Shear Zones (4-8)
4. Thermal structure & strength profiles (4-13)
5. Strength profiles 2. (4-15)

Part I: Applications 1.Toroidal (San Andreas, revisited) (4-20)

2. Collisions (Alps / Himalaya)? (4-22)
3. Rifts (Basin & Range vs EAR) (4-27)
4. Project talks (4-29)

ToDo 1: flow laws ToDo 2: Mechanism Maps ToDo 4: 1-D Thermal profiles ToDo 3: 0D shear zones/ wires ToDo 5: Strength Profiles lecture do Emphasis on concepts, processes and quantitative tools to think about how plates deform... with applications at the end...

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ToDo 1: flow laws ToDo 2: Mechanism Maps* ToDo 4: 1-D Thermal profiles* ToDo 3: 0D shear zones/wires ToDo 5: Strength Profiles* Independent Projects: 3 groups of 2? 1 on wire deformation experiments 2 on regional studies (each person on a different aspect? e.g. thermal structure/ seismic velocities/ viscosity and surface deformation patterns) T Graded EXAM*: conceptual questions, not calculations

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empirical,

bservation/

experiment, inductive ab initio, mechanistic, deductive phenomenological

The term phenomenology in science is used to describe a body of knowledge which relates empirical observations of phenomena to each

ther, in a way which is consistent with fundamental theory, but is not directly derived from theory.... The boundaries between theory and

phenomenology, and between phenomenology and experiment, are fuzzy. Some philosophers of science, and in particular Nancy Cartwright argue that any fundamental laws of Nature are merely phenomenological generalizations[2] (Wikipedia: Phenomenology_(science) ) The word "empirical" denotes information gained by means of observation, experience, or experiment... The standard positivist view of empirically acquired information has been that observation, experience, and experiment serve as neutral arbiters between competing theories. However, since the 1960s, Thomas Kuhn [2] has promoted the concept that these methods are influenced by prior beliefs and experiences. Consequently it cannot be expected that two scientists when observing, experiencing, or experimenting on the same event will make the same theory-neutral observations. The role of observation as a theory-neutral arbiter may not be possible. Theory-dependence of observation means that, even if there were agreed methods of inference and interpretation, scientists may still disagree on the nature of empirical data. (Wikipedia: Empirical ) A calculation is said to be ab initio (or "from first principles") if it relies on basic and established laws of nature without additional assumptions or special models. (Wikipedia: Ab_initio)

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from the siesmogenic layer down and the asthenosphere up..

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Part I: Deformation mechanisms 1.What is “high temperature”? (3-11)

2. Diffusion Creep (3-23)
3. Dislocation Creep (3-25)
4. Rocks: multi-scale materials (3-30)

Questions: By what processes do rocks deform at high temperature ?

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atomic scale

~1 nm silicon metal, atomic force microscopy

http://www.omicron.de/

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“dislocation” scale

Dislocations in

livine from

Hawaiian mantle nodule. Optical view, scale ~175 microns images source: http://ic.ucsc.edu/~casey/eart150/Lectures/DefMech/14deformationmechanisms.htm

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from T. Hiraga

http://www.eri.u-tokyo.ac.jp/hiraga/Preface.html

“grain” scale grain boundary:

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! ! " ! ! # !!# !!$ ! ! $ !!$ !% !% !% !% !& !& !& !& !" !" ! " !" !" !#

!"#$%&'(#)'*+#,-'.%/()0 1/$#!"#)2%+))#,34&0 45678#94&"#:5;<=8#>

' '

6 ; = 8 ? !; !67< 6 67< ; ;7< = =7< 8 !;@ !;? !;= !;6 !A !@ !? !=

deformation mechanism map

log

diffusion creep dislocation creep

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Undulose extinction in larger quartz grains reflection dislocations in crystal. Width of view 4 mm Recrystalization microstructure. Relatively strain- free grains with straight grain

boundaries. Width
f view 2 mm.

(CASEY) Microstructure of a

mylonite. Fine-

grained quartz-rich matrix surrounding relative rigid feldspar clasts. 1 cm width of view. image source: http://ic.ucsc.edu/~casey/eart150/Lectures/DefMech/14deformationmechanisms.htm

* * *not from here, but representative fabric rock “fabric”

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SW Ontario, from website of Chris Gerbi, University of Maine, Orono

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Part II: Rheology & Dynamics

1. Stress, strain, forms of suffering (4-1)
2. Viscoelasticity (Cheese), Thermodynamics (4-6)
3. Shear Zones (4-8)
4. Thermal structure & strength profiles (4-13)
5. Strength profiles 2. (4-15)

Questions: >How do we extrapolate micro-mechanisms to the Earth? >How do we describe (mechanically) deformation in the Earth ? >What are the structures and dynamics that lie beneath the seismogenic regions? >How do we infer processes at depth from the patterns of seismicity?

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Y Z e=0.375 !=3.6982 X

1. Stress, strain, forms of suffering (4-1)

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rheology: phenomenological models

2. Viscoelasticity, Cheese and Thermodynamics of Deformation (4-6)

viscoelasticity, anelasticity and attenuation...

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Montesi, Geophysical Research Letters, 2007

3. Shear Zones (4-8)

How do mylonites (ductile shear zones) form? Why and does strain localize? emphasis on grain size reduction... Zero-D shear zone:

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Work and Strain Energy

= L L

= F A = E

SE = 1 2 d

2LA

W = Fu = 1 2AL

strain stress elasticity Consider increasing stress from 0 to Strain energy work

So in this case. W=SE, 0=-W+SE, a conservative system

The Wire Deformation Experiments:

1. Constant force
2. vary mass and material
3. measure displacement, time
4. analyze data with

thermodynamic model

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Continental geotherms, constrained by P-T estimates of xenolith equilibration (McKenzie, Jackson & Priestley, EPSL 2005)

! !"# $ % &% $% '% (% )%% )&% )$% )'% )(% &%% *+,-./0 *+1/23456 % & $ ' % &% $% '% (% )%% )&% )$% )'% )(% &%% 17+--87+3491: )%%% )&%% )$%% )'%% % &% $% '% (% )%% )&% )$% )'% )(% &%% /+61+7:/87+34; <34)4=034$%4=0 <4:/4>"!?"@"

Density, pressure and temperature (from Equations of state and thermal conductivity)

4. Thermal structure & strength profiles (4-13)

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http://www1.eere.energy.gov/geothermal/geomap.html

estimated temperatures at a depth of 6 kilometers

Temperature, °C

The Structure and Physical Properties of the Earth’s Crust, Geophysical Monograph 14, editor John G. Heacock, pp. 169 – 184, 1971.

The Thermal Structure of the Continental Crust

DAVID D. BLACKWELL

measured heat flow at surface

http://smu.edu/geothermal/heatflow/

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5. Strength profiles 2. (4-15)

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Return to this image:

5. Strength profiles 2. (4-15)

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Part III: Applications 1.Toroidal (San Andreas, revisited) (4-20)

2. Collisions (Alps / Himalaya)? (4-22)
3. Rifts (Basin & Range / EAR) (4-27)
4. Project talks (4-29)

Thermal/compositional differences that lead to rheological differences? Boundary condition differences (i.e. plate forces) ? Feedbacks between the two? How to develop hypotheses for rheological explanations for morphological/structural differences in a setting? How to test those hypotheses?