Chap 2 Plate Tectonics Flashcards
PANGEA:
Supercontinent that existed prior to tectonic plate movement.
WEGNER’S EVIDENCE FOR CONTINENTAL DRIFT:
- Observation of fit of continents
- Locations of past glaciations
- Distribution of equatorial belts (coal, sand and salt deposits in a belt due to similar climates)
- Fossil distribution
- Matching geographical units
PALEOMAGNETISM:
Record of the ancient strength and orientation of Earth’s Magnetic Field
How do ROCKS DEVELOP PALEOMAGNETISM
molten rock cools -> minerals crystallise -> during cooling the
minerals are affected by earth’s magnetic field -> strength and orientation of magnetic field preserved.
POLAR WANDER:
The successive positions of dated paleopoles trace out a curving line that came to be known as an apparent polar-wander path
the magnetic field dipole of earth is 11⁰ off of earths geographical poles, this difference is called the magnetic declination
POLAR WANDER: Hypothesis 1
(apparent polar wander path): earths
continents are fixed but the magnetic poles wander –
rejected as the study of palaeomagnetism didn’t show
and accurate belt of magnetic wander to prove this
POLAR WANDER: Hypothesis 2
earths continents move but poles are
fixed – approved by
palaeomagnetism
PALEOPOLE:
a magnetic pole of the earth as it was situated at a time in the distant past.
SEA-FLOOR SPREADING
=continents drift apart because new
ocean floor forms between them by a process
Discovered by bathymetric maps that shows mid-ocean ridges (no sediment), submarine mountain ranges, trenches, seamount chains and fracture zones.
Harry Hess’ hypothesis of spreading:
marine magnetic anomalies show sets of positive and negative
alternating bands on ocean floor that are symmetrical to each other which explains magnetic field reversals and sea-floor spreading from mid-ocean ridges.
Subduction
continents move toward each other when the old
ocean floor between them sinks back down into the Earth’s interior
(The downgoing plate (the plate that sinks in the process of subduction)
must be composed of oceanic lithosphere.)
Plate tectonics
a theory that Earth’s lithosphere
consists of ~20 distinct pieces (plates) that slowly move relative to one another
PLATE BOUNDARIES:
when plate tectonics move, the internal part of the plate remains intact but the boundaries deform
PLATE BOUNDARIES: Types
- Divergent (constructive)
- Convergent (destructive)
- Transform
Divergent (constructive) PLATE BOUNDARIES
= A plate boundary at which two
plates move apart from each other
mafic rock – forms pillow lavas. (mid ocean ridge)
Convergent (destructive) PLATE BOUNDARIES
= A plate boundary at which two plates move toward each other so that one plate sinks
beneath the other
Subduction
occurs (oceanic-continental/oceanic)
or mountain ranges (continentalcontinental) (Andes mountains)
o Forms island arcs (2 oceanic
plates collide) or volcanic arcs (1 ocean plate and 1 continental)
o Wadati-benioff zone: belt of earthquakes on down-going plate
Wadati-benioff zone
belt of earthquakes on down-going plate
Transform: PLATE BOUNDARIES
plates slide past each
other (San Andreas Transform fault)
TRIPLE JUNCTION:
Three plate boundaries
intersect (west coast of South America)
HOT SPOT:
Places where a plume of hot mantle rock rises from just above the core-mantle boundary and causes anomalous volcanism at an isolated volcano
As a plate moves over the mantle plume, the
volcano moves off the hot spot and dies, and a new volcano forms over the hot spot. As a
result, hot spots spawn seamount chains
Mantle plume can lead to
eruptions when plate with volcanic/island arc
moves over it (Hawaii, Yellowstone)
