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 More Dense Less Dense

ISOSTACY – REACHING A BALANCE IN DENSITY

Fig.4.05 DISTRIBUTION OF EARTHQUAKES ON EARTH AREAS OF SPREADING – AREAS OF CONVERGENCE

Fig.4.03 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 may be determined by… –Assuming fixed hot spot locations –Measuring volcano age / distance along a hot spot track. Plate Velocities Plate 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

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 Margins Cascades Sierra Nevada Mts. Central America Andesitic/Rhyolitic Volcanism

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 W. W. Norton

Fig W. W. Norton

Palisades Sill: Rifting during Breakup of Pangea