Classroom presentations Classroom presentations to accompany to accompany

Understanding EarthUnderstanding Earth, 3rd edition, 3rd edition

prepared by

Peter Copeland and William Dupré

University of Houston

Chapter 21Chapter 21Deformation of the Continental Crust

Deformation of the Deformation of the Continental CrustContinental Crust

Deformation of continental Deformation of continental crustcrust• 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 AgoPangaea 250 Million Years Ago

Fig.21.1

Mountains and Mountain BuildingMountains 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 Structures of continentscontinents

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

andGrandfather of Plate Tectonics

Fig.21.1

Age of the Continental CrustAge of the Continental Crust

Fig.21.2

Blue areas mark continental crustbeneath the ocean

Fig.21.3

Major Major Tectonic Tectonic Features Features of North of North AmericaAmerica

Deformed and Metamorphosed Deformed and Metamorphosed Canadian ShieldCanadian Shield

Fig.21.4

Continental characteristicsContinental characteristics

• Granitic-andesitic composition

• 30–70 km thick

• 1/3 of Earth surface

• Complex structures

• Up to 4.0 Ga old

Three basic structural Three basic structural components of continentscomponents of continents

• Shields

• Stable platforms

• Folded mountain belts

Shields (Shields (e.g.e.g., Canada), 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 platformsStable 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 Mountain beltsbelts

• 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 Mountain typestypes

Folded—Alps, Himalaya, Appalachians

Fault block—Basin and Range

Upwarped—Adirondacks

Volcanic—Cascades

Stacked Sheets of Continental Crust Stacked Sheets of Continental Crust Due to Convergence of Continental Due to Convergence of Continental

PlatesPlates

Fig.21.5

Indian plate subducts beneath Indian plate subducts beneath Eurasian plateEurasian plate

Fig.21.6a

60 million years ago

Indian subcontinent collides with Indian subcontinent collides with TibetTibet

Fig.21.6b

40–60 million years ago

Accretionary wedge and forearc Accretionary wedge and forearc deposits thrust northward onto Tibetdeposits thrust northward onto Tibet

Fig.21.6c

Approximately 40–20 million years ago

Main boundary fault developsMain boundary fault develops

Fig.21.6d10–20 million years ago

Fig.21.7

Appalachian Appalachian MountainsMountains

Fig.21.8

A

A’Line of cross section

Physiographic Physiographic Provinces of Provinces of the Western the Western

United StatesUnited States

Cross section of the Cordillera Cross section of the Cordillera from San Francisco to Denverfrom San Francisco to Denver

Fig.21.9

A A’

Fig.21.10a

Volcanic Origin,Volcanic Origin,e.ge.g. Cascades. Cascades

Upwarped with Reverse Faults,Upwarped with Reverse Faults,e.ge.g. Central Rocky Mountians. Central Rocky Mountians

Fig.21.10b

Tilted Normal Fault Blocks,Tilted Normal Fault Blocks,e.ge.g. Basin and Range Province. Basin and Range Province

Fig.21.10c

Folded Rocks,Folded Rocks,e.ge.g. the Appalachian Ridge and . the Appalachian Ridge and

ValleyValley

Fig.21.10d

Overlapping Thrust Faults,Overlapping Thrust Faults,e.ge.g. the Himalayas. the Himalayas

Fig.21.1

Fig.21.11

Typical Basin and Range TopographyTypical Basin and Range Topography

Triassic Rift Valleys of ConnecticutTriassic Rift Valleys of Connecticut

Fig.21.12

Inferred Thickness of Mesozoic and Inferred Thickness of Mesozoic and Cenozoic Sedimentary RocksCenozoic Sedimentary Rocks

Fig.21.13

Idealized Cross SectionIdealized Cross Sectionof Basin and Dome Structuresof Basin and Dome Structures

Fig.21.14

Fig.21.15

Black Hills Black Hills of South of South Dakota:Dakota:a Dome a Dome

StructureStructure

Uplift Formed by Removal of Ice Uplift Formed by Removal of Ice SheetSheet

Fig.21.16a

Uplift Caused by HeatingUplift Caused by HeatingSubsidence Caused by CoolingSubsidence Caused by Cooling

Fig.21.16b

Uplift Caused by HeatingUplift Caused by HeatingSubsidence Caused by ExtensionSubsidence Caused by Extension

Fig.21.16c

Uplift Caused by Rising Mantle Uplift Caused by Rising Mantle PlumePlume

Fig.21.16d

Fig.21.17

Raised Beaches Due to Isostatic Uplift

Fig.21.18

Effects of subsidence on VeniceEffects of subsidence on Venice

Raised sidewalk

Fig.21.19

Present Rates of Present Rates of Uplift and SubsidenceUplift and Subsidence