Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 21 Deformation of the Continental Crust

Deformation of continental crust Since continents are not destroyed by subduction, we look here for the ancient history of Earth. orogenyorogeny: sum of the tectonic forces (i.e., deformation, magmatism, metamorphism, erosion) that produce mountain belts

Pangaea 250 Million Years Ago Fig.21.1

Mountains and Mountain Building Mountains are one part of the continuum of plate tectonics—the most evident one. Example: Limestones at the top of Mount Everest.

Structures of continents 1) Continents are made and deformed by plate motion. 2) Continents are older than oceanic crust. 3) Lithosphere floats on a viscous layer below (isostasy).

Alfred Wegener: Father of Continental Drift and Grandfather of Plate Tectonics Fig.21.1

Age of the Continental Crust Fig.21.2 Blue areas mark continental crust beneath the ocean

Fig.21.3 Major Tectonic Features of North America

Deformed and Metamorphosed Canadian Shield Fig.21.4

Continental characteristics Granitic-andesitic composition 30–70 km thick 1/3 of Earth surface Complex structures Up to 4.0 Ga old

Three basic structural components of continents Shields Stable platforms Folded mountain belts

Shields (e.g., Canada) Low elevation and relatively flat ”Basement complex" of metamorphic and igneous rocks Composed of a series of zones that were once highly mobile and tectonically active

Stable platforms Shields covered with a series of horizontal sedimentary rocks Sandstones, limestones, and shales deposited in ancient shallow seas Many transgressions, regresssions caused by changes in spreading rate

Mountain belts Relatively narrow zones of folded, compressed rocks (and associated magmatism) Formed at convergent plate boundaries Two major active belts: Cordilleran (Rockies-Andes), Alps-Himalayan Older examples: Appalachians, Urals

Mountain types Folded—Alps, Himalaya, Appalachians Fault block—Basin and Range Upwarped—Adirondacks Volcanic—Cascades

Stacked Sheets of Continental Crust Due to Convergence of Continental Plates Fig.21.5

Indian plate subducts beneath Eurasian plate Fig.21.6a 60 million years ago

Indian subcontinent collides with Tibet Fig.21.6b 40–60 million years ago

Accretionary wedge and forearc deposits thrust northward onto Tibet Fig.21.6c Approximately 40–20 million years ago

Main boundary fault develops Fig.21.6d 10–20 million years ago

Fig.21.7 Appalachian Mountains

Fig.21.8 A A’ Line of cross section Physiographic Provinces of the Western United States

Cross section of the Cordillera from San Francisco to Denver Fig.21.9 A A’

Fig.21.10a Volcanic Origin, e.g. Cascades

Upwarped with Reverse Faults, e.g. Central Rocky Mountians Fig.21.10b

Tilted Normal Fault Blocks, e.g. Basin and Range Province Fig.21.10c

Folded Rocks, e.g. the Appalachian Ridge and Valley Fig.21.10d

Overlapping Thrust Faults, e.g. the Himalayas Fig.21.1

Fig Typical Basin and Range Topography

Triassic Rift Valleys of Connecticut Fig.21.12

Inferred Thickness of Mesozoic and Cenozoic Sedimentary Rocks Fig.21.13

Idealized Cross Section of Basin and Dome Structures Fig.21.14

Fig Black Hills of South Dakota: a Dome Structure

Uplift Formed by Removal of Ice Sheet Fig.21.16a

Uplift Caused by Heating Subsidence Caused by Cooling Fig.21.16b

Uplift Caused by Heating Subsidence Caused by Extension Fig.21.16c

Uplift Caused by Rising Mantle Plume Fig.21.16d

Fig Raised Beaches Due to Isostatic Uplift

Fig Effects of subsidence on Venice Raised sidewalk

Fig Present Rates of Uplift and Subsidence