Download Deformation of the Continental Crust

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 the
Continental Crust
Deformation of continental crust
• Since continents are not
destroyed by subduction, we look
here for the ancient history of
Earth.
• orogeny: 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
Blue areas mark continental crust
beneath the ocean
Fig.21.2
Major
Tectonic
Features
of North
America
Fig.21.3
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
60 million years ago
Fig.21.6a
Indian subcontinent collides with
Tibet
40–60 million years ago
Fig.21.6b
Accretionary wedge and forearc
deposits thrust northward onto Tibet
Approximately 40–20 million years ago
Fig.21.6c
Main boundary fault develops
10–20 million years ago
Fig.21.6d
Appalachian
Mountains
Fig.21.7
Physiographic
Provinces of
the Western
United States
Line of cross section
A’
A
Fig.21.8
Cross section of the Cordillera
from San Francisco to Denver
A
A’
Fig.21.9
Volcanic Origin,
e.g. Cascades
Fig.21.10a
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
Typical Basin and Range Topography
Fig.21.11
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
Black Hills
of South
Dakota:
a Dome
Structure
Fig.21.15
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
Raised Beaches
Due to Isostatic Uplift
Fig.21.17
Effects of subsidence on Venice
Raised sidewalk
Fig.21.18
Present Rates of
Uplift and Subsidence
Fig.21.19