Chapter 2 - Plate Tectonics Flashcards
Francis bacon
Noticed that Africa fits with South America
Give evidence for theory of continental drift
1) fossils of Mesasorus found coming to South Africa and Brazil
2) Geological evidence (rocks of similar age, type and structure)
3) coal deposits found under Antarctic ice caps and glaciations scars in warm areas
4) mid Atlantic Ridge
- 1000km wide
- 2.5km high
- young volcanic rocks
5) earth’s magnetic pole has had 171 reversals over the last 76 million years
6) seafloor spreading
Earths layers
Oceanic crust
- consists of mainly basalt
- Average 6 to 10 km thick
Continental crust
-70 km thick
Mantle
- 2900 km deep
- temperature reaches 5000°C
1) upper mantle : composed of silicate rocks rich in iron and magnesium, and is rigid layer
2) asthenosphere - semi molten state
Core
-Consist of iron and nickel, and is the size of Mars
-Centre is 6371 km below earths surface
-temperature is 6200°C
Outer core is in a semi molten state and the inner core is solid
What moves tectonic plate
Convection cell currents
Magnetic declination
The Earth’s magnetic field tilt 11° to the planets rotational axis therefore the geographical poles of the Earth do not coincide exactly with the magnetic poles and this difference is called the magnetic declination
Palaeomagnetism
The record of ancient strength and orientation of the Earth’s magnetic field preserved in a rock
Polar wander path
A curved line traced out by success of positions of date at Paleopoles
What is a Paleopole
Refers to the supposed position of the Earth’s magnetic North Pole in the past
Mid ocean ridges
Elongated submarine mountain ranges who’s peaks lie only 2 to 2.5 km below sea level
Deep ocean trenches
When the ocean floor reaches depths of 8 to 12 km which define elongated gated trenches
Seamount chains
Chain of isolated submarine mountains which were once active volcanoes
Fractured zones
Narrow band of vertical fractures at roughly right angles to mid ocean ridges
Describe the nature of the oceanic crust
Much of the ocean floor is covered by a layer of sediment composed of Clay and the tiny shells of dead plankton but ocean ridges have no sediment on.
Contains no Grannite and no metamorphic rock
Common rock types on continents but only contains basalt and gabbro
Active and passive plate boundaries
Active plate boundaries coincide with tectonic plate boundaries
Passive plate boundaries do not coincide with tectonic plate boundaries and characteristic of such plate boundaries is the development of a continental shelf
Continental shelf
Abroad, shallow region on the surface of a thick accumulation of sediment cover that were deposited along a massive margin with a continental crust is thinner the norm
Divergent plate boundary
A plate Boundary at which two plates move apart from each other
Convergent plate boundary
A plate Boundry at which two plates move towards each other so that one plate sinks beneath the other
Transform plate Boundary
A boundary at which one plate slips along the side of another plate
Explain plate tectonics
The lithosphere of the Earth is divided into plates that move relative to one another and to the underlying asthenosphere
During plate movements the internal area of the plates remains largely rigid and intact but rock along the plate Boundry undergoes D formation
Sea floor spreading
As to oceanic plates move apart, new oceanic lithosphere forms along the divergent boundary.
Process takes place at mid ocean ridges
Pillow lava
Lava that spills from mid ocean ride axis and cools instantly to form a layer of basalt blobs on the sea floor
Black smoker
Chimneys that spew hot mineralised water that rose through cracks in the sea floor, after being heated by magma below the surface
Subduction
As two plates move towards each other, the oceanic plate may collide, or one plate Bends and sinks down into the asthenosphere beneath the other plate
Downgoing and overriding plate in convergent boundaries
The plate that sinks in the process of subduction must be composed of oceanic lithosphere
The plate that does not sink in the subduction process can consist of either oceanic or continental lithosphere
Wadati Benioff zone
A belt of earthquakes in the down going plate to a depth of 660km
accretionary prism
a wedge shaped mass that includes sediment that had settled on the surface of the downgoing plate that gets scraped up during the subduction process
volcanic arc
magma formed above the downgoing plate rises into the overriding crust and finally to the surface to form a chain of active volcanoes that parallels with the ocean trench
forearc and back-arc region
forearc region is the area between the trench and the arc
the back-arc region is on the side away from the trench
triple junctions
places where three plate boundaries intersect at a point
hot spots
places where a plume of hot mantle rock rises from just above the the core-mantle boundary and causes abnormal volcanism at an isolated volcano
