Transcript Appalachian Mountains

Section 20.1
Crust-Mantle Relationships
Objectives
Describe the elevation distribution of
Earth’s surface.
Explain isostasy and how it pertains to
Earth’s mountains.
Describe how Earth’s crust responds to
the addition and removal of mass.
Section 20.1
Crust-Mantle Relationships
Earth’s Topography
Topography is the variation in elevations of
Earth’s crust.
Topographic maps show differences in elevation
on Earth’s surface.
Section 20.1
Crust-Mantle Relationships
Earth’s Topography
When Earth’s topography is
plotted on a graph, a pattern
in the distribution of
elevations emerges. Most of
Earth’s elevations cluster
around two main ranges of
elevation—0 to 1 km above
sea level and 4 to 5 km
below sea level.
Section 20.1
Crust-Mantle Relationships
Earth’s Topography
Continental crust
Continental crust is thicker and less dense
than oceanic crust, so it extends higher
above Earth’s surface and deeper into the
mantle than oceanic crust.
Section 20.1
Crust-Mantle Relationships
Isostasy
The displacement of the mantle by Earth’s
continental and oceanic crust is a condition
of equilibrium called isostasy.
Section 20.1
Crust-Mantle Relationships
Isostasy
Gravitational and seismic studies have
detected thickened areas of continental
material, called roots, that extend into the
mantle below Earth’s mountain ranges.
Section 20.1
Crust-Mantle Relationships
Isostasy
Mountain roots
A mountain range requires large roots to
counter the enormous mass of the range
above Earth’s surface.- like a tree.
Continents and mountains are said to float
on the mantle because they are less dense
than the underlying mantle. They project
into the mantle to provide the necessary
buoyant support.
Section 20.1
Crust-Mantle Relationships
Isostasy and Erosion
The Appalachian Mountains in the eastern
United States formed hundreds of millions
of years ago when the North American
continent collided with Europe and Africa.
Section 20.1
Crust-Mantle Relationships
Isostasy and Erosion
As the Appalachian Mountains rose(was
forming) above Earth’s surface, deep roots
formed until isostatic equilibrium was achieved
and the mountains were buoyantly supported.
As peaks eroded, the mass decreased. This
allowed the roots themselves to rise and
eventually erode.
Section 20.1
Crust-Mantle Relationships
Isostasy and Erosion
A balance between erosion and the
decrease in the size of the roots will
continue for hundreds of millions of years
until the mountains disappear and the
roots are exposed at the surface.
Section 20.1
Crust-Mantle Relationships
Isostasy and Erosion (like ice floating in water)
The slow process of the crust’s rising as the
result of the removal of overlying material is
called isostatic rebound.
Erosion and rebound allows metamorphic
rocks formed at great depths to rise to the top
of mountain ranges such as the Appalachians.
Section 20.1
Crust-Mantle Relationships
Isostasy and Erosion
Seamounts
Individual volcanic mountains produced by
hot spots under the ocean floor are called
seamounts. As a result of isostasy, the
oceanic crust around these peaks
displaces the underlying mantle until
equilibrium is achieved.
Section 20.2
Orogeny
Objectives
Identify orogenic processes.
Compare and contrast the different types of
mountains that form along convergent plate
boundaries.
Explain how the Appalachian Mountains formed.
Section 20.2
Orogeny
Mountain Building at
Convergent Boundaries
Orogeny refers to all processes that form
mountain ranges.
Broad, linear regions of deformation
commonly known as mountain ranges are
also known in geology as orogenic belts.
Section 20.2
Orogeny
Mountain Building at
Convergent Boundaries
Most of Earth’s
mountain ranges
formed along
plate boundaries.
Section 20.3
Other Types of Mountain Building
1.Divergent-Boundary Mountains- ocean ridges.
Underwater volcanic mountains known as
ocean ridges form a continuous chain that
snakes along Earth’s ocean floor for over
65,000 km.
Section 20.3
Other Types of Mountain Building
Divergent-Boundary Mountains
An ocean ridge is a broad, topographic high
that forms as lithosphere bulges upward due
to an increase in temperature along a
divergent boundary.
Section 20.2
Orogeny
2.Mountain Building at
Convergent Boundaries
At convergent plate boundaries, compressive
forces squeeze the crust and cause intense
deformation in the form of folding, faulting,
metamorphism, and igneous intrusions.
Interactions at each type of convergent boundary
create different types of mountain ranges.
Section 20.2
Orogeny
Mountain Building at
Convergent Boundaries
a.Oceanic-oceanic convergence
Convergence between
two oceanic plates
results in the formation
of individual volcanic
peaks that make up an
island arc complex.
Section 20.2
Orogeny
Mountain Building at
Convergent Boundaries
b.Oceanic-continental convergencevolcanic mountain ranges.
At an oceanic-continental boundary,
compression causes continental crust to fold
and thicken. Igneous
activity and
metamorphism are
also common along
such boundaries.
Section 20.2
Orogeny
Mountain Building at Convergent
Boundaries
3.Continental-continental convergence
Intense folding and faulting
along continental-continental
boundaries produce folded
mountains - highest mountain
ranges on Earth.
presence of marine
sedimentary rock near the
mountains’ summits.
Section 20.2
Orogeny
The Appalachian Mountains—A
Case Study
Geologists have divided
the Appalachians into
several distinct regions.
Each region is
characterized by rocks
that show different
degrees of deformation.
Section 20.2
Orogeny
The Appalachian Mountains—A
Case Study
The early Appalachians (P.572, Fig 20.13)
The tectonic history of the Appalachians began
about 800 to 700 mya when ancestral
1. North America separated from ancestral
Africa along two divergent boundaries to form
two oceans— the ancestral Atlantic Ocean and
a shallow, marginal sea. A continental fragment
was located between the two divergent
boundaries.
• 2. 700-600 mya Atlantic ocean began to
close , an island arc formed(Piedmont
province)
• 3. 500-400 mya continental fragment (Blue
Ridge province)attached to N.America.
• 4. 400-300 mya Island arc(Piedmont
province) attached to N.America.
5. 300-260 mya Pangea forms, further
compression results in the folded Valley and
Ridge province.
Section 20.3
Other Types of Mountain Building
Objectives
Identify the processes associated with
non-boundary mountains.
Describe the mountain ranges that form
along ocean ridges.
Compare and contrast uplifted and
fault-block mountains.
Section 20.3
Other Types of Mountain Building
Mountains on the ocean floor and some
mountains on continents form through
processes other than convergence.
Review Vocabulary
normal fault: a crack in Earth where the rock
above the fault plane has dropped down
Section 20.3
Other Types of Mountain Building
1.Uplifted Mountains
Uplifted mountains
form when large
sections of Earth’s
crust are forced
upward without much
structural
deformation.
Section 20.3
Other Types of Mountain Building
Uplifted Mountains
When a whole region is uplifted, a
relatively flat-topped area called a plateau
can form.
Erosion eventually carves these relatively
undeformed, uplifted masses to form
peaks, valleys, and canyons.
Section 20.3
Other Types of Mountain Building
2.Fault-Block Mountains
Fault-block mountains
form between large
faults when pieces of
crust are tilted, uplifted,
or dropped downward.