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, thin 5-30km Crust: Rigid, Thin Mantle: Plastic, Convecting

Tectonics and Structural Geology Tectonic Stresses resulting from Internal 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 and Releases energy  Earthquakes

Fig. 10-CO, p. 216

Folds and Faults (Palmdale, Ca) See Fig. 10-2a, p. 219

Eastern Pennsylvania Northwestern Africa

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 Ohio Using Dipping Bedding Planes Beds Dip 2 o, West Younger rocks, West Mirror image east of Sandusky? Beds Dip 2 o, West Younger rocks, West Mirror image east of Sandusky? Sandstone Shale Limestone M O D 2o2o 2o2o 2o2o

Anticline (fold)

Syncline (fold)

Plunging Anticline

Fold Terminology Axis Axial Plane Plunging Age of rocks and outcrops Axis

Plunging Anticline, Colorado

Eastern 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 a, 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 Graben Horst 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 b, 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 Tensional Structures

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?