Earth History GEOL 2110

Theory of Plate TectonicsPart 2:

Elements of Plate Tectonics

Major Concepts• Plate Tectonic theory posits that the earth outer layer

(lithosphere) is composed of rigid plates that are moving relative to each other; Plates are composed of either thin oceanic crust or thick continental crust overlying upper mantle

• Plate boundaries that are diverging are where new oceanic crust is being created as the mantle upwells, decompresses and partially melts.

• Plate boundaries that are converging involve one oceanic crust plate subducting beneath another or a continental edge. This triggers earthquakes and explosive volcanism resulting from partial melting of a hydrated mantle wedge

• Orogenesis occurs when continental crust encounters continental crust

Plate Tectonic Theory The Earth’s outer shell (lithosphere) is composed of rigid plates that

are moving relative to one another.

Internal Structure of the EarthCompositional Layers

Physical Layers

Plate Tectonics Drives Two Stages Crust-making A. Mantle partially melts to make ocean crust

B. Ocean crust partially melts to make continental crust

What Moves the Plates?Mantle Push Ridge Slide

Slab Pull

Types of Plate Boundaries

Divergent Plate BoundariesMid-ocean Ridges

Where Stage 1 Crust is Made

BasaltRock Type of the Ocean Crust

Pillow Lavas

Remember:Melting the mantle makesmafic magma!! Always

Hydrothermal Alteration of Ocean CrustPreparing it for Stage 2 Melting

“Black Smokers”- metal-rich hydrothermal waters venting into the ocean floor

Continental Rifting :The creationof new ocean basins

Continental Rifting and

The Break-up of Pangea

Age of the Atlantic Ocean CrustRecording the Break-up

Beginning the Break-up225 Ma

Youthful Oceanic Crust

Convergent Boundaries

Making 2nd Stage Crust

Ancient Continental Crust

Convergent BoundariesWhere the Action Is!!

Ocean-Continent

Continent - Continent

Ocean - Ocean

Earthquakes

Volcanoes

Mt. St. HelensMay 18, 1980

Consequences of ConvergenceExplosive Volcanism

Consequences of Convergence

Mountain Building and Rock Deformation

Consequences of Convergence Earthquakes

Banda Ache, Dec. 26, 2004

OROGENESISThe Culmination of Convergence

Ancient OrogensLooking into the Roots of Mountain Belts

Penokean Orogen

St. CloudJay Cooke

Transform Fault Plate Boundaries

San Francisco EarthquakeApril 18, 1906 Mag 7.8The San

Andreas Fault

Mantle Plumes/Hotspots

Mantle Hotspots in the OceansSites of over-

thickened crust and the

formation of ocean islands and plateaus

Famous Hotspots

Hawaii

Yellowstone

Iceland

Sedimentary Basins and Plate Tectonics

Evolution of Sedimentation during Arc-Continent Collision

The Grand Unifying Theory of the Earth

FRIDAY

Midterm Exam 1

Chapters 1 to 7