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Geol 117 - Plate Tectonics Review sheet for Exam 1

History of Oceanography/ Ocean Exploration

First: the compass

sighting on the sun and stars

still a problem with longitude

making charts and logs

navigation for commerce

first accurate clock 1761 (solves the longitude problem partly)

the Challenger Expidition - first specifically for science

Exploration in the 1800s - the polar seas, water sampling

World Wars and the development of modern oceanography

Origin of the Oceans

Origin of the solar system

Origin of Earth 4.6 Ga

Geologic Time (Hadean, Archean, Proterozoic, Phanerozoic)

Finding your way about the Earth

Latitude and Longitude

Map Projections

How much and where is the land and water

What is ave. depth of oceans (how is ocean depth distributed)

modern Navigation (GPS)

Cycles

Seasons

Hydrologic cycle

Mid-ocean ridges - origin

Divergent plate boundaries
Spreading centers:
-Creation of new oceanic lithosphere,
-Volcanic activity, Hydrothermal Activity
Earthquakes -- Tensional forces
Variation in width caused by variation in spreading rates:
Fast spreading = wide ridges
Slow spreading = narrow ridges

Photos of hot water vents and solidified lavas

Birth of a Divergent Boundary

Rift forms in a plate
Above: Earliest stages of divergence
Below: Later, as oceanic crust begins to form
Occurring in East Africa
Continental rift systems
(e.g., East African Rift)
Developing" divergent boundaries
Eventual formation of new ocean
Break-up of continents (like Pangea!)

Fracture Zones are Transform plate boundaries

Breaks in the ocean crust connecting the segments of the mid-ocean ridges
Ridge crests offset by fracture zones
Earthquakes along offseting middle segments only
Segments that offset ridge axes are Transform Plate Boundaries with Earthquakes
Long segments of fracture zones beyond the offset portions are old, "inactive" boundaries

Marginal trenches ­ description

Western Pacific:

Volcanic island chains on the upper plate
Zone of deep, strong earthquakes

Eastern Pacific:

Volcanoes on continent (Andes, Mt. St. Helens)
Zone of deep, strong earthquakes
(Maps showing shallow earthquakes and deep earthquakes)

Ocean-ocean convergence -- Western Pacific

Subduction of which ever plate is older, cooler
Volcanism -- melting during descent of plate
Earthquakes -- friction in the "cool" plate and between plate and mantle

Ocean-continent convergence -- Eastern Pacific

Subduction of the oceanic plate- why?
Volcanism? -- same as ocean-ocean.
Earthquakes? -- same as ocean-ocean.

Continent-continent convergence, or collision zone

Continental plates not subducted -- too bouyant
Mountains, earthquakes
Example: Himalayas (India-Asia collision beginning 45 m.y. ago)

Ocean basins - How can we explain their features using plate tectonics theory?

Deep sea floor features:

Abyssal plains
Age and thickness of sediments
Volcanic features
Abyssal hills
Submarine seamounts
Guyots
Coral atolls
Chains of volcanic islands (e.g., Hawaii)

Ocean basins - origin: Oceanic lithosphere that has cooled and subsided as it spreaded away from mid-ocean ridges

Subsidence explains guyots and atolls
Sediment distribution -- fits prediction of ocean-crust age
Volcanic islands and seamount chains

The Hot Spot Concept

Stationary plume of hot mantle material
Plate migrates over plume
Active volcanoes- over plume
Extinct volcanoes- moved away from plume

Guyots

1. Volcanic island
2. Volcanic activity stops
3. Subsidence and erosion
4. Flat top formed as the island is worn down
5. Continued subsidence

Sediment accumulation- thicker away from ridges
Subsidence- ocean floor deeper away from ridges

Lithosphere is older, so it's cooler, and denser- does not stand higher any more, like it did when it was first formed (i.e., like a Mid-ocean ridge)

MAGNETIC PROPERTIES OF THE SEA FLOOR

Magnetic alignment of iron minerals in lavas established during cooling- permanent
"Reversals" of Earth's magnetic field
Magnetic "anomaly" pattern of the sea floor:

Stripes parallel to and symmetrical across mid-ocean ridges
Interpretation: Continuous creation of oceanic crust over millions of years, during which magnetic reversals occur.

The Ocean Adjacent to Continents

Active vs. Passive margins

Continental Shelves (exposed during ice ages)

Continental Slope

Continental Rise

Submarine Canyons

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