Transcript Rheology

Rheology
Structures of the deeper crust
An intro-3/19.02
Outline of today’s
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Weak rocks and flow
Diapirism of salt
Stress-strain experiments at higher P, T
The brittle-ductile transition
Deformation and re-crystallization
Salt diapirs - known for a long time
Intrude sedimentary sections
Important oil traps
DIAPIRS
Gulf of Mexico
salt diapirs
Some of the best of all salt diapirs_ Zagros, Iran
Salt Valley Utah
Cross-section through diapirs
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
What do we learn from salt?
• Rocks can behave in a non-brittle fashion
• Flow of rocks!! (especially over geologic time
scales)
• Need to investigate the rock mechanics at higher T
and P; could granites flow at 20 km?
• Remember that crustal earthquakes are confined
to within the upper 10-15-20 km; any mechanical
significance?
Limitation of
experiments:
size of the
system
matters,
maybe, but
most
importantly
TIME
Strain rate is
the rate over
which %
deformation is
applied
The brittle and the ductile crust
The implications
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Earthquakes no deeper than transition
Lower crust can flow!!!
Lower crust decoupled from upper crust
No strength to the deeper crust.
A more complete picture
And so how does a “ductile” rock look like? Can we see
them at the surface of the Earth? Can we simulate their
textures? Can we study their strain /stress regimes?
Such rocks are commonly exposed throughout
the continents. Not as common as the shallow
rocks, of course. Rocks that were at as deep as
150 Km are seen at the surface of the Earth sometimes they contain diamonds!!!!!!
SOOO… we can attempt to study deformation in
the deeper Earth.
P
T
Relationships between deformation and metamorphism
•Connection between structural processes and metamorphism;
Tectonites are subject to grain-size reduction but because this process
take place at high pressures-temperatures, tectonites are also subject to
grain growth via recrystallization.
time
Static recrystallization
Dynamic recrystallization
Rotation of grains
Summary
• Continuous deformation in the deeper crust
is mostly ductile;
• Effectively rocks can “flow” over geologic
time scales
• Forget faults, large-scale folds; instead
penetrative deformation at smaller scale
• Deformation is intimately associated with
metamorphism