Lecture 7: Plate Tectonics Flashcards by Ashley De Guzman

Father of Plate Tectonics

Alfred Wegener

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Pangaea

Supercontinent

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1915

The Origin of Continents and Oceans

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Political Problem of Plate Tectonics

Alfred Wegener is German while most of the geosciences was based in US and Britain

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Proofs of Continental Drift Theory

• Matching fossils in continents
separated by large waters
• Matching geological patterns
• Karoo Glaciation found in South America, Africa, Australia, and Antarctica which can only happen (according to Wegener) if they
were connected.

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What moved the continents according to Alfred Wegener?

1The continents are icebergs on heavier SiMa crust
2Forces available to push the continents are
• Earth rotation effect
• Lunar and solar tidal forces

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The proposal of Hess on sea floor spreading was called?

GEOPOETRY

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Geopoetry was released on what year

1962

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What are the ideas under Geopoetry?

•Ocean Ridges form new seafloor (from mantle material) while the old
seafloor is pushed and subducts to be reintroduced to mantle
• Movement is driven by mantle convection cells (remember the convection
currents where material goes up in ridges and goes down at trenches?)
• Continental crust does not descend but are lifted up as mountains – only
oceanic crust descends.

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What year was magnetometer readings done to study ocean floor topography

1961

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He noticed that the magnetic pattern is symmetric with respect to ocean ridges. The pattern showed alternating stripes of normal and reverse
magnetic polarity of rocks.

Vine

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1963

Vine and Matthews (Vine’s Ph.D. supervisor) proposed

that the patterns are related to magnetic reversals.

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The material from the mantle that rises up through the midocean ridge is______ that contains magnetite – a rock mineral that is highly magnetic and aligns with the magnetic field.

basalt

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How are the stripes and magnetic reversal related?

• The material from the mantle that rises up through the midocean ridge is basalt that contains magnetite – a rock mineral that is highly magnetic and aligns with the magnetic field.
• As the material hardens, the magnetic field recorded gets “locked in” in the rock.
• Material is created again at the ridge, pushing out the
material before it
• When the earth’s magnetic field reverses, it is also recorded in the material. Hence the symmetry of magnetic record with respect to mid-ocean ridges)

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Who is Morley?

Morley is also another geologist who came up

with the same idea independently from Vine and Matthews.

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Who is John Tulzo Wilson?

Proponent of Mantle plume or Hot Spot

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Hot Spot

• Spot where hot mantle material goes up through the
crust and up above the surface.
• It is non-moving and semipermanent

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Hot Spots are found aroun the world mostly in ocean basins, name a hot spot found in a continent

Yellowstone hotspot

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Oceanic ridges appear curved but are actually straight. The curve in the ridges are caused by offsets caused in turn by faults perpendicular to the ridge. What are these faults called?

Transform Fault

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1965

Tuzo coined the term Transform Fault

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At transform faults, plates

Move in opposite direction

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Introduced the ideas of “plates” making up the crust.

John Tulzo-Wilson

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1967

Plate maps are made

Name the Major plates (Top to bottom and Left to Right)

Eurasia, North America, Australia, Pacific, South America, Africa, India, and Antarctic

Plate Tectonic's Rate of motion

1 – 10 cm/yr

The movement of Plate Tectonics

Translational and Rotational

Name the types of Plate Boundaries

Divergent, Convergent, Transfrom

Spreading boundaries

Dirvergent

Crustal material created by Diverging plates

mafic igneous rock – Basalt or Gabbro

How are Pillow Lavas form?

Pillow lavas are formed when the lava flows out into the water

How are Sheeted Dykes form?

Formed when the ridge opens up and a | column of magma cools in the crack.

3 types of convergent boundaries

* Ocean – Ocean * Ocean – Continental * Continental - Continental

Ocean Trenches form from what type of convergent boundary

Ocean-ocean

Which plate submerges during ocean-ocean convergence?

The Denser plate (older and colder)

How are chain of volcanic islands form?

During o-o convergence, Magma forms underneath (via flux melting*) and rises up

Which plate submerges during ocean-continent convergence?

Oceanic Platee

This is formed during o-c convergence when accumulated sediment on continental slope is thrust up

Accretionary Wedge

Happens when the plate has moved so much

Continental-continental Convergence

Why are 2 continental plates both lifted up during convergence?

Because no plate is denser

Plates slides across each other without creation or destruction of crustal material.

Transform Boundary

Upwelling of mantle causes newer and warmer | material to form that will in turn be pushing older and colder material away from the ridge.

Ridgepush

Older and colder plate segments at subduction zones | become colder and denser thus goes down further and pulls the rest of the plate attached to it

Slab pull

Which moves faster? Plates with or without subducting part?

With

Does bigger area means bigger traction velocity

No. Plate area is not related to its velocity

Main mechanisms of plate movement

1 Convection 2 Ridge push 3 Slab pull

3 magma forming plate-tectonic setting

* Divergent boundary (via decompression melthing) * Convergent boundary (via flux melting) * Mantle plume (via decompression melting)

Melting or partial melting of hot rock as pressure on it is reduced (while temperature remains roughly the same)

Decompression Melting

When water is added into a rock, it lowers the melting | point of the rock.

Flux Melting

Composite volcanoes form at ________ boundaries

Convergent

shield volcanoes are formed from

Mantle plumes, continental rifting

the elongation/stretching of the crust in some areas resulting to its thinning. Since it is thin, it allows rising of mantle material. It forms shield volcanoes and cinder cones

Continental Rifting

This can be observed in mantle plumes, divergent | boundaries and ocean-ocean convergent boundaries.

Seafloor volcanism

What percent of utramafic mantle becomes mafic magma in the zone of partial melting>

~10%

rocks are buried deep (10-20km | typically), usually related to convergent boundaries, and spans thousands of km^2

Regional Metamorphism

a body of magma in the upper part of crust can be the source of heat and metamorphose rock around it. The zone of contact metamorphism is a few meters up to tens of meters.

Contact Metamorphism

Resulting rock of Oceanic crust metamorphism on either side of the ridge

Greenstone and Greenschist