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 CrystallizationBowen’s Reaction Series

More Dense

Less Dense

ISOSTACY – REACHINGA 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 pushSlab 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 may be determined by…– Assuming fixed hot spot locations

– Measuring volcano age / distance along a hot spot track.

Plate Velocities

Plate velocitiesPlate velocities

Tectonic plates

• All plates move continuously relative to one other.- Motion ranges from 1 to 15 cm/yr

• Plates interact along boundaries- Divergent

- Convergent

- Transform

Tectonic plates: Earth’s lithosphere is divided into ~20 plates

Tectonic plates: Earth’s lithosphere is divided into ~20 plates

Three types of Convergent Margins

WHAT HAPPENS TO A PLATE WHEN IT SUBDUCTS?

Formation of Intermediate Composition Magmas

Partial Melting and Crustal Rock Assimilation

Convergent MarginsCascadesSierra Nevada Mts.

Central America

Andesitic/RhyoliticVolcanism

OCEAN-OCEAN COVERGENCE

Mt. Fuji Volcanic Activity at Ocean-Ocean Boundary

Accretion of ContinentsThrough Accretion onthe Margins

CONTINENT-CONTINENT COVERGENCE

MAJOR MOUNTAIN RANGES COMMONLY COINCIDEWITH 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