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SEAFLOOR SPREADING – YES!!
1. HOW DOES THIS RELATE TO THE FORMATION OF
THE OCEAN FLOOR?
2. IS THE EARTH GETTING BIGGER?
3. HOW DOES THE FORMATION OF NEW OCEAN FLOOR
RELATE TO THE DEFORMATION OF THE EARTH’S
SURFACE?
Intrusive Mafic Igneous Rock -- Gabbro
Sequence of Crystallization
Bowen’s Reaction Series
Less Dense
More Dense
ISOSTACY – REACHING
A BALANCE IN DENSITY
DISTRIBUTION OF EARTHQUAKES ON EARTH
AREAS OF SPREADING – AREAS OF CONVERGENCE
EARTH IS CONSTRUCTED OF SOLID TECTONIC PLATES
OCEAN-CONTINENT COVERGENCE
Driving Mechanisms
Slab pull-Ridge push
• Ridge push – The higher elevation of the MOR pushes the adjacent
lithosphere away.
• Slab-pull – Once an oceanic plate begins to subduct, it pulls the rest
of the plate with it
• Plates may be slowed or hastened by convection in asthenosphere
Plate Velocities
Plate velocities
• Plate velocities may be determined by…
– Assuming fixed hot spot locations
– Measuring volcano age / distance along a hot spot track.
Tectonic plates
Tectonic plates: Earth’s lithosphere is divided into ~20
plates
• All plates move continuously relative to one other.
- Motion ranges from 1 to 15 cm/yr
• Plates interact along boundaries
- Divergent
- Convergent
- Transform
Three types of Convergent Margins
WHAT HAPPENS TO A PLATE WHEN IT SUBDUCTS?
Formation of Intermediate Composition Magmas
Partial Melting and Crustal Rock Assimilation
Andesitic/Rhyolitic
Volcanism
Convergent Margins
Cascades
Sierra Nevada Mts.
Central America
OCEAN-OCEAN COVERGENCE
Mt. Fuji Volcanic Activity at Ocean-Ocean Boundary
Accretion of Continents
Through Accretion on
the Margins
CONTINENT-CONTINENT COVERGENCE
MAJOR MOUNTAIN RANGES COMMONLY COINCIDE
WITH THE MARGINS BETWEEN CONVERGENT PLATES
The Wilson Cycle
Fig. 13.20
W. W. Norton
Fig. 13.22
W. W. Norton
Palisades Sill: Rifting during Breakup of Pangea