Age of the Earth. Subdivisions of geologic time –Eon, Era, Period, Epoch –Eons Precambrian: 4.5...

Age of the EarthAge of the Earth

• Subdivisions of geologic time– Eon, Era, Period, Epoch

– Eons• Precambrian: 4.5 b.y. to ~0.5 b.y.

• Phanerozoic: ~0.5 b.y. to today

Geologic time scaleGeologic time scale

• Subdivisions of geologic time– Eon, Era, Period, Epoch

– Eras• Paleozoic: ~560 m.y. to ~250 m.y.

• Mesozoic: ~250 m.y. to ~65 m.y.

• Cenozoic: ~65 m.y. to today

Geologic time scaleGeologic time scale

Image source: http://www.gly.fsu.edu/~salters/GLY1000/12Rock_record_time/Slide27.jpg

Plate Tectonics- OverviewPlate Tectonics- Overview

• Plate Tectonics–General Principles

• Plate Movements–Accumulating Evidence

• Types of Plate Boundaries

• How Far, How Fast, How Long, How Come?

• Plate Tectonics and the Rock Cycle

Plate Tectonics–General Plate Tectonics–General PrinciplesPrinciples

• Stress and Strain in Geologic Materials

• Lithosphere and Asthenosphere

• Locating Plate Boundaries

TectonicsTectonics

• Stress- application of a force– Compressive (pushing together)– Tensile (pulling apart)

• Strain- deformation response of the force– Elastic deformation: ‘rubber band’– Plastic deformation: permanent strain– Rupture: the breaking point

Folding Rock

Source: Photograph courtesy of M.R. Mudge; courtesy USGS Photo Library, Denver, CO.

Folding and Faulting, Cook Inlet, Alaska

Source: Photograph by N.J. Silberling, USGS Photo Library, Denver, CO.

Rock Failure Under Stress

Source: Photograph courtesy of W.B. Hamilton; courtesy USGS Photo Library, Denver, CO.

Effect of tectonics on rocksEffect of tectonics on rocks

• Depends of physical conditions– Temperature & pressure

– composition, time, fluids

Lithosphere- AsthenosphereLithosphere- Asthenosphere

Lithosphere-AsthenosphereLithosphere-Asthenosphere

• Lithosphere (lithos = rock)– Brittle, elastic outer layer

– ~50 km under oceans, ~100 km under continents

• Asthenosphere (asthenes= without strength)– Plastic domain

– ~300 km in mantle

– Discovered by seismic wave studies

Plate boundariesPlate boundaries

• Deformation, earthquakes, and volcanoes are not evenly distributed around the Earth

• Mostly concentrated in linear belts, chains• Can use distribution to ‘map out’ plates• ~8 major plates, several smaller ones

World Locations of Volcanoes and Earthquakes

Source: Map plotted by the Environmental Data and Information Service of NOAA; earthquakes from U.S. Coast and Geodetic Survey.

Plate Movements–Accumulating Plate Movements–Accumulating EvidenceEvidence

• The Topography of the Sea Floor

• Magnetism in Rocks–General

• Paleomagnetism and Seafloor Spreading

• Age of the Ocean Floor

• Polar-Wander Curves

• Other Evidence

Shaded Relief Map of the World

Source: Photo courtesy of NOAA National Geophysical Data Center.

Shaded Relief Map of the World

Source: Photo courtesy of NOAA National Geophysical Data Center.

The Earth is a large bar magnet…

And sometime it flips…!

(1) Minerals oriented randomly in a melt

(2) Minerals aligned in the magnetic field

Minerals: the ‘Curie Temperature’

First magnetic survey of the oceans

Age Distribution of the Sea Floor

Source: Marine Geology and Geophysics Division of the NOAA National Geophysical Data Center.

World Locations of Volcanoes and Earthquakes

Source: Map plotted by the Environmental Data and Information Service of NOAA; earthquakes from U.S. Coast and Geodetic Survey.

World Lithospheric Plates

Source: After W. Hamilton, U.S. Geological Survey.

Source: http://www.mq.edu.au/scienceresearch/lackie.htm

Polar Wander

Plate Movements — Today

Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75:4939-4956, 1970, copyright by the American Geophysical Union.

Plate Movements — 100 Million Years Ago

Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75:4939-4956, 1970, copyright by the American Geophysical Union.

Plate Movements— 200 Million Years Ago

Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75:4939-4956, 1970, copyright by the American Geophysical Union.

Glacial Deposits Across Southern Continents

Source: After Arthur Holmes, Principles of Physical Geology, 2d ed., Ronald Press, New York, NY, 1965.

Types of Plate BoundariesTypes of Plate Boundaries

• Divergent Plate Boundaries– Rifts, Mid ocean ridges, lots of volcanism

• Transform Boundaries– Sliding plates, lots of earthquakes

• Convergent Plate Boundaries– Subduction zones, mountain belts

Divergent plate boundary: East African Rift

Satellite Image of Lake Tanganyika, Africa

Source: © NASA

Transform plate boundary: San Andreas strike-slip fault

Convergent plate boundary: Subduction Zone in Alaska

Source: Image courtesy of NOAA National Geophysical Data Center.

Convergent plate boundary: Where are we?

Current Motions of Major Plates: Satellite laser data

Source: Data from NASA.