Plate Tectonics Flashcards
Who was Alfred Wegener? What was his hypothesis?
A German meteorologist. Hypothesized that the continents used to fit together as a single
supercontinent he named Pangaea.
Where are earthquakes often found?
mid-ocean ridges, transform faults, and deep-sea trenches.
Name 3 pieces of evidence to support the existence of Pangea…
- Glacial Deposits
- Similar species/organisms
- Mountain Belts
Is the inner core liquid or solid? outer core?
Inner core: Solid
Outer core: Liquid
Hot magma - has no magnetic orientation
Cool magma (as it turns solid) - magnetic signature becomes frozen in the rock
What is Sonar?
Allows a ship to easily measure sea-floor bathymetry.
Based on the travel time of sound waves generated by the ship and reflected off the bottom.
What was Harry Hess’ hypothesis?
Compiled the evidence that new sea floor is created at mid-ocean ridges, moves away from the ridges, and then subducts back into the mantle.
What is Normal Polarity and Reversed Polarity?
Normal Polarity - how magnetic dipoles are today
Reversed Polarity - North end of a compass would point south
When does a positive anomaly form?
When the polarity of the sea floor is the same direction of the polarity of the Earth.
When does a negative anomaly form?
When the polarity of the sea floor is the opposite direction of the polarity of the Earth.
Are positive anomalies strong or weak?
Positive anomalies = strong
Negative anomalies = weak
How are magnetic anomaly stripes created?
As the mid-ocean ridge adds new basalt to the spreading oceanic crust
Where can you find the youngest oceanic floor?
Near the mid-ocean ridges
Name the three types of plate boundaries.
- Convergent - move towards each other
- Divergent - move away from each other
- Transform - move sideways past each other
What is an example of a convergent boundary? divergent? transform?
Convergent - Overriding plate
Divergent - Mid-ocean Ridge
Transform - Shear/Strike-slip
What are Active Continental Margins?
found on the leading edge of the continent where it is crashing into an oceanic plate. Common site for tectonic activity.
What are Passive Margins?
The transition between oceanic and continental lithosphere which is not an active plate margin.
What is “Ridge Push”?
develops by the gravitational energy associated with the topographic elevation of the mid-ocean ridge.
What is “Slab Pull”?
develops because the old oceanic lithosphere is more dense than the underlying asthenosphere, so it sinks.
What two things does the Lithosphere consist of?
The crust and the uppermost mantle
What is the Wadati-Benioff zone?
A planar zone of seismicity corresponding with the down-going slab in a subduction zone (660km depth)
What is an accretionary prism?
a mass of sedimentary material scraped off a region of oceanic crust during subduction and piled up at the edge of the overriding plate.
What produces a continental volcanic arc?
Subduction along the edge of a continent. Sediments on the downgoing slab are scraped off to form an accretionary prism.
What produces an oceanic volcanic arc?
When two oceanic plates collide, the volcanic arc forms on the overriding plate.
What is a triple junction?
A place where three plates intersect at a point.
What are hot-spot volcanoes?
A consequence of mantle plumes. As a plate drifts over the hotspot, a chain of extinct volcanoes (a “hot-spot track”) forms.
What is an example of a hot-spot track? What do they do?
The Hawaiian Islands. They provide clues to the
direction of plate movement.
What is the process of rifting?
When continental lithosphere stretches and thins, the upper crust breaks by faulting. Upwelling asthenosphere initiates volcanism. Rifting may split a continent in two.
Why doesn’t continental crust subduct?
It is too buoyant to subduct, so when two continents converge, rock undergoes compression and shearing, and a mountain range develops.
Relative Plate Velocity
Describes motion of one plate relative to another.
Absolute Plate Velocity
Describes motion compared to a fixed reference point in the mantle.
The zone of the Earth that is divided into plates is the…
Lithosphere
The observation that magnetic anomalies that constitute magnetozonesare found as far back in time as one can find appropriate rocks to measure indicates that:
The Earth has always had a convectingportion of its core over that time period
How many times has the Earth’s ocean floor been
created and destroyed?
Atleast 25 times
