Chapter 2 Plate Tectonics Flashcards
What was Alfred Wegener’s first piece of evidence for Continental Drift Hypothesis?
The similarities in the coastlines of South America and Africa.
Why are fossils important to the hypothesis of Continental drift?
Similar rocks, fossils, and glacial formations were formed on continents that do not currently have conditions for these geological features. Ex: Glacial till in Australia
What important piece was Alfred Wegener missing to help prove the theory for continental drift?
A mechanism for how the continents moved. (convection in the mantle is the major force of plate movements, along with gravity and density)
Which scientist proposed the theory of seafloor spreading?
Harry Hess
What is the theory of seafloor spreading?
Mid-ocean ridges (divergent plates) spread and force new material to the surface, while creating new seafloor.
What is Paleomagnetism?
When in liquid state, minerals align themselves with Earth’s magnetic field. When the rock cools, the alignment is frozen in place. Kind of like a fossilized compass
In which layer of the earth do most earthquakes occur?
The crust
Is continental crust more dense or Oceanic crust?
Oceanic crust (think, subduction along continental boundaries)
Which layer of Earth is the largest chemical layer by volume?
The mantle, to a depth of 2900 km.
What does the inner core mainly consist of
A very dense iron core.
What are the five physical layers?
Lithosphere, Asthenosphere, Mesosphere, Outer and Inner core
The Lithosphere is the outermost physical layer of Earth. What two types of lithosphere are there?
Continental and Oceanic Lithosphere
Which layer drives the movement for tectonic plates?
The Asthenosphere. (Astheno means lacking strength)
What is the mesosphere?
Called the lower mantle. More rigid and immobile than asthenosphere. Located 410 to 660 km below Earth’s surface. Minerals continuously change into various forms in this zone.
What physical layer is the only entirely liquid layer?
The Outer Core.
What keeps the inner core solid?
The immense pressure keeps the minerals of the inner core in a solid phase.
What generates the earth’s magnetic field?
The circulation of molten iron and nickel within the Outer Core.
True or false: North and South America’s eastern coastlines are examples of active margins
False (passive margin)
Convergent boundaries move _____
Toward each other (destructive boundaries)
What two types of convergent boundaries are there?
Subduction and collision, depending on density
Where does subduction most often occur?
Between Oceanic plates and Continental plates
As an oceanic plate descends, it pulls the ocean floor down into a trench. What is the average yearly rate of oceanic plate subduction?
Half an inch per year
When ocean floor sediments are scraped together and compressed between subducting plates and overriding plates, what is this called?
The accretionary wedge.
When land mass is added to continental plates from ocean floor subduction, what is this called?
Terrane
When the subducting oceanic plate sinks deep into the mantle…. ___________
The immense heat and pressure push material under the continental plate, forming liquid magma which is forced up as volcanism. (See Cascade Range)
Which type of plate boundary is known for having the largest earthquakes?
Convergent boundaries (Subduction zones)
What is the result of Oceanic-Oceanic subduction?
Volcanism, and can result in island arcs
What occurs when continental plates converge?
The plates do not subduct, and instead, collision occurs. Often characterized by tall, non-volcanic mountains. (See: Alps)
Constructive boundaries
Divergent
What are the two types of Divergent boundaries?
Continental rift zones and mid-ocean ridges.
What two factors determine if continental rifting occurs?
A) Does not occur in continents with older and stable interiors, known as Cratons
And B) When rifting occurs, the breaking pattern resembles truncated icosahedron (seams on a soccer ball)
What two types of rifts are there?
Narrow and broad
What is an example of active narrow rifting?
The East African Rift Zone
What are the characteristics of Mafic rocks?
Darker in color and contain more minerals that are dark in color.
As oceanic lithosphere continues to diverge, a _________ - ___________ ridge is formed
Mid-ocean
What is created at mid-ocean ridges?
New lithosphere
Ridge formation suggests that sections of lithosphere furthest away from mid-ocean ridges will be the oldest. How do scientists test this theory?
Comparing the age of rocks from various locations on the ocean floor. Sediment closest to the mid-ocean ridges will be very thin as well.
What is the cause of magnetic anomalies along mid-ocean ridges?
As magma is released, Earth’s magnetic field is imprinted into the magma. As the spreading continues, these magnetic fields change the further you get from the ridge.
Mid-ocean ridges are often studded with _____________________
Hydrothermal vents
What is a transform boundary often called?
Strike slip or conservative boundary
A boundary where lithospheric plates slide past each other in a horizontal plane
Transform boundary
The San Andreas fault is an example of what type of boundary?
Transform boundary
When transform boundaries are unable to shear past each other, pressure builds up resulting in…
Earthquakes
_____________ occurs where there is a component of compression in addition to shearing
Transpression
When a geological feature is cut by a fault it is called…
A piercing point.
A _________ is an area in the lithospheric plate where molten magma breaks through and creates a volcanic center
Hotspot
The only type of volcanism NOT associated with subduction zones
Hotspots
