Deformation and .mountain building
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Transcript of Deformation and .mountain building
X. Deformation and . Mountain Building
A. Plate Tectonics and Stress
B. Rock Deformation
C. Geologic Structures
D. Origin of Mountains
E. Continental Crust
Tectonic Stresses Large Scale Strain of the Crust i.e., Geologic Structures
Inner core: Solid iron Outer core: Liquid iron,
convecting (magnetic field)
Mantle (Asthenosphere) : Solid iron-magnesium silicate, plastic, convecting
Crust (Lithosphere): Rigid, thin5-30km
Crust: Rigid, Thin
Mantle: Plastic, Convecting
Tectonics and Structural Geology
Tectonic Stresses resulting fromInternal Energy (heat driving convection) Strains (deforms) the Mantle and Crust
Bends Rocks, i.e., ductile strain (Folds)Breaks Rock, i.e., brittle strain (Joints) and Moves large blocks along Faults andReleases energy Earthquakes
Fig. 10-CO, p. 216
Folds and Faults (Palmdale, Ca)
See Fig. 10-2a, p. 219
Eastern PennsylvaniaEastern Pennsylvania
NorthwesternAfrica
Stresses at Plate
Boundaries Divergent (Tensional)
| Convergent (Compressional) | Transform (Shear)
e.g., Pacific NW
Geologic Structures Different stresses result in
various forms of strain (geologic structures) Folds (compressive
stresses may cause ductile strain)
Faults (Any type of stress may cause brittle strain. The type of fault depends on the type of stress)
Stikes and Dips are used to identify geologic structures
Strike and Dip
Define and map the orientation of planar features Bedding planes (sedimentary rocks) Foliation Joints Faults Dikes Sills Ore Veins
Fig. 10-4, p. 221
Strike and Dip
Strike: The line of intersection between the plane and a horizontal surface
Dip: Angle that the plane makes with that horizontal plane
Fig. 10-4, p. 221
Strike and Dip Map Symbol
Sipping Bedding Planes
Youngest (top) P: Permian P: Pennsylvanian M: Mississippian D: Devonian S: Silurian O: Ordovician C: Cambrian
Oldest (bottom)
D
S
O
Sedimentary Rocks Dip in the direction of younger rocks
Deciphering the Geology of OhioUsing Dipping Bedding Planes
Beds Dip 2o, West Younger rocks, West Mirror image east of
Sandusky?
Beds Dip 2o, West Younger rocks, West Mirror image east of
Sandusky?
Sandstone Shale Limestone
M O D2o2o2o
Anticline (fold)
Anticline (fold)
Syncline (fold)
Plunging Anticline
Fold Terminology
Axis Axial Plane Plunging Age of rocks
and outcrops
Axis Axis
Plunging Anticline, Colorado
Eastern PennsylvaniaEastern Pennsylvania Folds and faults resulting from
compressive stresses Anticlines (many plunging) Synclines (many plunging) Reverse faults Thrust faults
Domes and Basins
Bedrock Geology of the Michigan Basin During and after
the deposition of Michigan’s sedimentary rocks
The crust warped downward
Exposing younger rocks in the center and
Older rocks on the rim (e.g. Toledo)
When shallow crust is strained rocks tend to exhibit brittle strain
Brittle Strain Joints
Sheet Joints
Defining Fault Orientation
Strike of fault plane parallels the fault trace and fault scarp
Direction of Dip of the fault plane indicates the Hanging wall block
Fig. 10-11a, p. 227
Fault: Movement occurring along a discontinuity Brittle strain and subsequent movement as a
result of stress Fault
terminology
Faults
Fault: When movement occurs along a discontinuity
Fault type depends on the type of stress
Normal Faults
Normal Faults, Horsts and Grabens
Structures at Divergent Boundaries
Tensional Stresses cause brittle strain and formation of sets of normal faults
i.e., Horsts and Grabens
Horsts and Grabens Older Rocks are exposed along the ridges
formed by the horsts
Younger rocks lie beneath the grabens Sediment fills in the linear valleys
Horst GrabenHorst
Graben
Nevada
“Washboard topography” is the result of Horsts and Grabens
A.k.a, Basin and Range E.g., Humbolt Range E.g., Death Valley
(Graben)
Horst and Graben, Nevada
Humboldt Range, Northern Nevada Fig. 10-15b, p. 233
Graben
Horst
Horst and Graben, Nevada
Humboldt Range, Northern Nevada
Graben
Horst
Reverse and Thrust Faults
Compressive stress causes the hanging wall to move upward relative to the foot wall Reverse Fault
At convergent plate boundaries ancient rocks can be thrust over younger rocks Thrust Fault
Structures at a Passive Continental Margin
Resulting from continental breakup E.g., The Americas and Africa
Salt Domes: e.g., Texas
Rising of less dense salt
Stretches overlying crust
Forming normal faults and
Oil traps
Structural Oil Traps
Thrust Fault: Glacier NP, Montana
Old
Younger
Structures at a Convergent Boundary
Structures within Mountain Belts
Compressional and TensionalStructures
E.g., The Apls
Intense folding and thrusting of sedimentary rocks
Strike Slip Faults
Physiographic Features
San Andreas Fault
What type of fault is this? What other features are
associated with the fault?