Tectonic plates Flashcards
GPS (evidence for plate tectonics theory)
GPS satellites are used to determine precise locations of instruments through triangulation
.By measuring one location continuously, the distance moved over the time of measurement can be determined.
Gps can measure the movement of tectonic plates, and their velocity
Hot spots/mantle plumes
Hotspots and mantle plumes are the same, a place in the Earth which is disproportionately hot, rock heats and rises up, melts due to decompression
Hot rock undergoes decompression melting, forming magma that can feed volcanic activity
Hot spots record plate motion by leaving a chain of volcanoes along its direction of movement
mid ocean ridges and magnetism
Earth’s magnetic field is generated by movement of molten iron in the outer core. It is extremely important as it protects us from solar winds.
Magnetic orientation of earth is changing! And it has done so spontaneously throughout earth’s history.
Normal polarity is when the north pole was where it is today
Reverse polarity is when the north pole was at the present day south pole
Magnetic materials in most rocks align with earth’s magnetic field as they cool, becoming tiny magnets
These rocks can tell us what the earth’s magnetic field was like at the time of formation
At mid ocean ridges, we see patterns of polarity as rocks form over time, strips of normal, reverse, normal, symmetrical on both sides
Transform boundaries
Plates sliding along one another
Also known as a transform fault, these zones occur when plates slide past one another; No new lithosphere is created.
Not normally associated with volcanism, but highly associated with earthquakes
rock age at mid ocean ridges
Crust is youngest at the plate boundary, and is older the further away from the plate boundary you are.
Older crust is denser than younger crust
mid ocean ridges
Occur at divergent oceanic-oceanic boundaries
Mantle upwelling occurs as plates pull apart.
Decompression melting occurs as the hot material is subject to less pressure.
New rock formation occurs at mid-ocean ridges.
Process is known as seafloor spreading
Seafloor spreading is why oceanic rock is younger than continental rock. New igneous rock is being formed at mid ocean ridges.
Rift Valley
Two continental plates pull apart from one another
Fractures (faults) form in both plates near the boundary
Slab between faults eventually ‘falls’, creating the rift.
divergent boundaries general
Plates moving away from each other
Mostly occurs in oceans at mid ocean ridges
If it occurs with ocean-ocean crust, it will form a mid ocean ridge
If it occurs with continental-continental crust, it forms a rift.
Convergent boundaries
Plates moving toward each other and colliding, leading one plate to subduct
Subduction
Denser plate subducts, either OCEANIC or OLDER
What happens depends on types of crust involved
Subduction
Subduction is the ‘sinking’ of of one lithospheric plate below another at a convergent boundary. Which plate subducts depends on the crustal types at the boundary.
velocity of pacific plate/plates on average
The Pacific Plate moves northwest at a speed of between 7-11 cm per year
Tectonic plates on average move 0.6 to 10 cm per year
Inner core
Creates Earth’s magnetic field
Hottest part of the Earth, temp between 5000-6000 degrees Celsius
Roughly 1400km thick
Mostly iron and nickel
solid
Outer core
Layer surrounding inner core, approximately 2400km thick
Mostly made of liquid iron and nickel
Mantle
Mostly oxygen, silicon, magnesium
2900km thick (thickest layer of Earth)
Lower Mantle
below lithosphere and asthenosphere
Just as hot as upper mantle, remains solid due to pressure, slowly moving due to convection currents
Convection currents - when deeper hotter material rises, then cools, then sinks again, though to move the Earth’s tectonic plates (happen here)
