GreatBreak: Grand Challenges in Geodynamics

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GreatBreak Grand Challenges in Geodynamics
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Characteristics of a Desirable Geodynamic Model

• Ties together observational constraints on
  current state of the lithosphere/upper mantle
  with physical/chemical processes as currently
  understood
• Process-oriented
• Multi-disciplinary
• Useful
• a hypothesis testing tool (is my interpretation
  consistent with the physical/chemical processes
  as we know them?)
• an exploratory tool that helps identify which of
  many are the dominant controlling processes.
• a predictive tool that can be used to guide
  future studies
• an analysis tool that helps constrain physical
  properties

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Driving Mechanism

• Potential Energy plays a role, but what else?
• Relation to Plate Boundary Processes
• Basal Shear
• Slab Windows, Mantle Drips, and Delamination
• Are Driving Mechanisms viewed differently at
  different depths, places, and scales?
• gt We need Better kinematic history at all
  scales detailed mantle images at ca. 50-100 km
  scales density structure T(x,y,z) and heat flow
  data.

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Rheology of the Lithosphere

• Is it net strength, or the jelly sandwich
  model? gt Thin Sheet vs. Fully Dynamic models.
• Is deformation style more strongly related to
  boundary conditions, or dynamically evolving
  rheological structure?
• What role does tectonic inheritance play?
• Does the P.E. concept apply to the lithosphere as
  a whole, or do we need a mobile layer (e.g.,
  weak lower crust) to facilitate collapse?
• gt We need More laboratory constitutive data
  more lab and field thermal data a direct
  comparison of the various modeling approaches.

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Coupling Deformation at Different Depths

• Decollement tectonics controls surface faulting,
  but what controls the decollement?
• The flat moho problem, lower crustal flow, and
  underplating
• Coupling mantle and crust. Is the uppermost
  mantle strong or weak?
• gt We need data of deep deformation rates
  patterns better information on age composition
  of lower crust more rheological and thermal
  data.

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List of Challenges

• Driving Mechanism for Extension
• Rheology of the Lithosphere
• Coupling Deep and Shallow Deformation
• Spatial and Temporal Changes in Patterns of
  Deformation and Magmatism
• Thermal Processes Mode of Isostatic
  Compensation
• Role of Fluids
• Understanding Faulting
• Exporting our Knowledge

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Exporting our Knowledge

• How do we incorporate all these knowledge pieces
  into a useful geodynamic model?
• Great Basin as a prototypical diffuse zone of
  continental extension
• What does it tell us about other parts of the
  Basin and Range?
• The West Antarctic Rift System?
• Why arent diffuse zones of continental extension
  more common? And why isnt the Great Basin an
  narrow rift?
• gt What we need A cross-disciplinary involvement
  in model development a community approach to
  model-building a geodynamic modeling tool that
  can be used by non-geodynamicists education on
  how to undertake outreach infrastructure
  support.

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Spatial and Temporal Changes in Deformation
Magmatism

• The relation between deformation and magmatism is
  still uncertain
• Tectonic inheritance vs. dynamic controls
• Sevier plateau local preexisting
  heterogeneities
• Dynamic temperature changes effect on strength
• Changes in melt source vs. time
• Lithosphere vs. asthenosphere
• Contributions from the crust
• gt We need easily queried data base of timing,
  location, rates, and geochemistry of faults
  magmatism

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Role of Fluids

• Rheological effects
• Generally weaken rocks in both brittle ductile
  regime
• May cement fractures
• Source
• Relation to thermal regime
• gt We need mapping of fluid flow indicators,
  correlation to structural elements, knowledge of
  volumetric flow rates knowledge of fluid types
  (hydrous fluids vs. melt).

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Thermal Processes Isostatic Compensation

• Patterns of heat flow
• Vertical and horizontal
• Role of fluid flow
• Causes and effects
• Wheres the heat coming from?
• How does T(x,y,z,t) relate to changes in
  deformation pattern?
• Turning on and off melt production
• Asthenosphere thermal state (then and now)
• Whats holding up the lithosphere?
• gt We need more physical properties heat flow
  data indicators of thermal state in the past
  more detailed images of the upper mantle.

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Faults

• Nucleation growth of Fault Systems
• Relationship between Fault Systems and regional
  local stress state (and how it varies with depth)
• Understanding low angle normal faults
• gt We need More detailed kinematic indicators of
  fault slip history fault system geometries
  More rheological data Better numerical algorithms