my background: CRUSTAL DEFORMATION (TTh, 1:10-2:25, 603 - - PowerPoint PPT Presentation

CRUSTAL DEFORMATION (TTh, 1:10-2:25, 603 Schermerhorn), second half: Ductile plate deformation (14 lectures) Ben Holtzman (benh@ldeo.columbia.edu), Lamont, Seismology Bldg, room 220. course work: 2 MATLAB-based homework/projects Research project (either individual paper or group experiment) 1 final exam ============================ lecture 1 (March 9): Overview Design and philosophy of the course: moving between empirical, phenomenological & mechanistic approaches. Overview of relevant length and time scales for processes in question. Overall driving questions: How do rocks, as earth materials, deform at all scales? A comparative approach applied to real orogens and rifts: What kinds of structural / dynamic features do we want to be able to explain ?

my background: ScB: geology (ophiolites) MSc: structural geology (in Oman) & mechanical models PhD: experimental (& theoretical) rock deformation now: the theoretical tools for extrapolating from experiments to earth conditions, and mapping between seismic velocities & viscosity-- applications to plate boundary structure and dynamics this course (what lies beneath Part 1): High T deformation mechanisms, rheology & plate deformation,

• bservation of structures and

microstructures (+ other kinds) continuum mechanics & thermodynamics

Length Scale Time Scale 10

• 14

per second 10 mantle convection (viscosity) seismic waves (elasticity)

============================ PART 1: Deformation mechanisms and rock fabrics By what processes does stress cause deformation in earth materials? lecture 2 (Mar 11): Diffusion Creep What is "High Temperature"?: Atomic motion and diffusion (brief statistical mechanics perspective); How does stress cause diffusion and shape change? Pressure solution and diffusion creep, lattice and grain boundary diffusion Rock textures associated with diffusion creep. (in class: Rock & micrograph observation) Experimental data, Flow Law and Deformation mechanism maps (for only D.C.) lecture 3 (Mar 23): Dislocation creep Single dislocations (TEM images) Dislocation organization, work hardening and annealing Theory: stress field around a dislocation, energetics of organization Recrystallization mechanisms and LPO development Flow law and mechanism map (add to diffusion creep map) Experimental and natural observations of textures: (in class: Rock & micrograph observation) Quartz: regimes in experiment (Hirth & Tullis) and field ( Hirth, Dunlap & Teyssier). Olivine: Stress estimates from experiments and nature: Xenoliths & Moine thrust (Kohlstedt and Weathers), (ice, if interest?) **MATLAB Homework/Project 1: calculate and modify deformation mechanism maps (3D projection to 2D) for different minerals (quartz, feldspar, olivine, pyroxene), extract trends with changes in stress, grain size, temperature, etc ... lecture 4 (Mar 25): Complex patterns in real rocks Interactions of deformation mechanisms in monophase rocks Rocks as polyphase materials: Rheologically contrasting phases Strain partitioning & Localization: Ductile fabrics & Multi-scale/fractal organization of shear zones Effects of fluids / melt: Deformed granites: magmatic vs solid state Stress-driven organization of melt

atomic scale

~1 nm silicon metal, atomic force microscopy

http://www.omicron.de/

“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

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

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”

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

============================ PART 2: Dynamics and Rheology How do we describe dynamic behavior of materials and evolution of strain ? lecture 5 (Mar 30): Large Strain in the Earth Pure shear, Simple shear, General Shear (MATLAB + appendix) Shear Zones, Folds, Diaprism, Convection (many scales) **MATLAB Homework/Project 2: Calculations of rheological evolution with zero- D shear zones, increasing in rheological complexity over the next two lectures. lecture 6 (Apr 1): Phenomenological Rheology Viscoelasticity, Plasticity, Viscoelastoplasticity (The Cheese Lecture) lecture 7 (Apr 6): Thermodynamics of shear zones Zero-D shear zones (ODEs), with intro to non-equilibrium thermodynamics: Stored and dissipated energy, illustrated with metals (Chrysocoos experiments). Phenomenological and empirical flow laws, i.e. elastic loading and plastic yielding. Description of real evolution processes: Grain size evolution and shear heating. lecture 8 (Apr 8): Rheological structure of plates Thermal structure of plates and strength profiles (and their limitations). Develop a 1-D thermal diffusion code for lithospheric temperature profile; Map stress using flow laws to construct "strength profiles"; Focus on the assumptions that go into the meaning of strength profiles and their limitations.. Consider other ways of looking at "strength". **Research Projects: Decide on topics, hand in one-page proposals

rheology: metals and cheeses

Luders bands

Montesi, Geophysical Research Letters, 2007

============================ PART 3: Applications to Plate Deformation on Earth With ideas from previous two sections, and Chris's part of the course, how do we interpret geological structures in terms of deformation processes and rheological evolution ? lecture 9 (Apr 13): Appalachians Historical overview of the orogens; "thin/thick skin"

• deformation. How do we compare deeply exhumed belts vs

modern ones ? lecture 10 (Apr 15): Western North America: Laramide/ Cordillera/SAF Historical overview, Evolution of SAF, ala Tanya Atwater. Present structure from EARTHSCOPE seismology and geodesy. lecture 11 (Apr 20): Alps/Himalaya Compare/contrast deformation styles along the length of the whole system. Review numerical models of himalaya ? lecture 12 (Apr 22): Extensional systems: East African Rift / Basin & Range comparison of initial lithospheric structure and tectonic boundary conditions. lecture 13 (Apr 27): Extensional systems continued... lecture 14 (Apr 29): Synthesis, large open questions... 10-minute presentations of research projects

“Plate tectonics is the surface expression of mantle convection” but HOW do the plate motions express the motions in the interior? “marginal LAB” “basal LAB” far-field plate driving force: convecting mantle drag: The rheology of the LABs are at the heart of this question!

Emile Argand, d.1940

Emile Argand, d.1940