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?