EESA06 Lecture 4
Topics for Lecture 4 and for Quiz 3 on Thrusday Feb 10th
1) Introduction to mid-}v]PWD}vvv]v^&}]o_DKZ~ooKZ]}o]
2) Why are more MORs Fractured? The role of transform faults
3) Iceland: Walking over a Mid-Ocean Ridge
4) Magnetic Stripes Recorded in Ocean Floor Crust and The Age of Ocean Floors
5) Basalt Lava Flows: Fissure Eruptions
6) Volcanic Activity Under Glaciers: Jokulhlaups!
7) Geothermal Energy
Oceans only widen(rift) to a certain width then they start to
close - subduction
- cooling away from ridge and thickens at sides
- It wants to sink back down to the mantle
- History of continent is dictated by ocean history
Ophiolites t Ancient pieces of ocean crust
- Combining the information can put a picture of
history of MORs
- Contain rocks that are very mineral-rich
Mid Ocean Ridge
- Middle of Atlantic, constantly volcanic eruptions
- Are not continuous, are fractured
Fractures t horizontal lines on MORs
- enable ocean floor spreading on a curved earth
surface
Dykes t result of hot magma intruding into older rock, sheeted
Dykes - surrounding rock will be extended
- basic fuel behind plate tectonics
Plumes t supply the large amounts of magma
How Oceans Widen: Continuous intrusion of dykes
- continuous cooling of margins of magma chamber
and continuous intrusion of new magma at center
- symmetrical distribution on each side
Pillow Basalt t pillowed lava, rounded masses where basalt magma was cooled very quickly
Gabbro t chemically equivalent of basalt but has larger crystals since it cools slowly, igneous rock
Peridotite t dominant mineral is olivine (Peridot), the mantle is made out of peridotite
Distill t Gabbro and Basalt is distilled from huge
mantle plumes
Ridge Push- Hot magma pushes up and dykes intrude
Slab pull - Ocean floor sinks under its own weight
Continental crust - is the product of melting ocean
crust plus sea water
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Ma t Mega-annum (million)
Ga t Giga-annum (billion)
ka t kilo-annum (thousands of years)
750Ma to 350Ma
- closing of an ocean t aiapotis
- oceanic crust t some gets subducted, some gets
pushed up onto land (Himalayas)
- Ophiolites t ancient ocean crust that is now on
land, fossil ocean crust preserved on land
Eastern Canada:
Chert (Flint) t sediments that were being slowly deposited on
top of MORs, igneous processes, and accumulates
Sheeted Dykes t continuous intrusion of basalt
Pillow Lava t igneous rock, cooled very quickly
Oceanic crust is made of:
- Mafic and Ultra-Mafic rockt magnetism and iron,
pre-dominant in olivine
Contiential crust is made of:
- Acidic Rocks t more silica
Red t is young Green + Blue is old
Youngest Rocks are all along the MOR
Pacific ocean can see old rock but not along south American coast
- Oceanic crust has already been subducted
- Feeding Andian Volcano, has been recycled
Maximum age of oceanic crust is:
- Late Jurassic (150 mill. years ago) t Pangea broke up
Continent underlay by two plumes,
push two contintents apart,
flood basalts develop into oceans
fractures allow spreading on curved surface or when there is
weakness in the crust
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