Unit 2: Tectonic Plates

Determine the plate velocity (speed AND direction) in cm/year for sections A and B based the information on the map below. Note: 1 km = 1000 meters, 1 meter = 100 cm Are these plate velocities reasonable compared with current plate velocities on Earth?What direction has this plate been moving through time and at what rate?

- 1.33 cm/yr & 1.25 cm/yr - For the first 47 Ma, the plate was moving west and once it hit 2 Ma, the plate began to shift and move southwest. - I would say they are not because average plate motion is 2-5 cm/yr and the velocity of this plate is slower than that.

Discuss 5 lines of evidence he used to support the existence of Pangaea.

- Distribution of Fossils: fossils of different organisms that would need a certain climate to stay alive were found in different continents which would have been difficult or unlikely if land masses were not together at some point. - Matching Rocks and mountain ranges: continents on either side of the north Atlantic Ocean have mountain ranges that line up and have familiar and similar structures - Climate reconstruction: rocks in some continents from over 300 billion years ago have striations from ice sheets and icebergs - Fit of the continent: he found that the edges of each continent would line up and fit together like a puzzle piece even though they would not line up perfectly because of weathering and erosion throughout the years. - Glacial data: striations and signs of glacial deposits were found in continents that today are not known for being cold or having ice sheets. This indicates that these continents had to be at higher latitudes at some point in time.

How is Earth's magnetic field formed? What specifically contributes to its generation and behavior?

Earth's magnetic field is formed the solidification of Earth's liquid iron core. It is generated by electric currents produced by the convection that goes on in Earth's outer core with the mixture of molten iron and nickel.

A divergent boundary like a continental rift will occur when continental lithosphere collides with continental lithosphere.

F

Earth's magnetic field is currently in a normal polarity where magnetic north is in the Southern Hemisphere and coincides perfectly with geographic South Pole.

F

What are 2 types of convergent plate boundaries? How are they different and why? List a present-day example of each

Subduction zones: when oceanic plate meets continental plate; oceanic plate subducts (slides under) the continental plate Collision zone: two continental plates meet and collide creating volcanoes or volcanic arcs

Why are the asthenosphere and lithosphere important to plate tectonics?

The lithosphere is where tectonic plates are located it which sits on top of the plastic, constantly deforming asthenosphere that is moving. It helps us understand how these plates move and where land mass goes especially when talking about convergent boundaries.

Explain in detail how the following observations are explained by plate tectonics: b. Global earthquake distribution

global earthquake distribution can be explained by plate tectonics because it allows us to understand why in certain places of the world there tends to be more earthquakes than at others. For example, California has more earthquakes than North Carolina because it is near a transform plate boundary (Juan de Fuca fault).

partial melting

rock is heated or depressurized to the melting point of some (but not all) of its minerals - different minerals have different melting temperatures

geotherm

the change of temperature with depth

List the 3 main types of plate boundaries. Summarize the processes that occur at each. What features would you use to identify each?

- Divergent boundary: a boundary in which two plates move away from one another. We typically see these as mid-ocean ridges where newer, and hotter rock comes to the surface at the ridge axis and older rock moves away as it cools. - Convergent boundaries: a boundary in which two plates meet and either the subduction process takes place or collision. In subduction, one plate slides underneath the other curving into the mantle. When an oceanic and continental plate meet, the oceanic plate goes under because it is denser than the continental plate. When an oceanic plate undergoes collision or said subduction, a trench is created when older and denser plates are pushed beneath newer and less denser plates. - Transform boundaries: in a transform boundary two plates slide past one another. In this type of boundary, lithosphere is neither created nor destroyed and many are found at the seafloor. They create faults that look like stair cases.

low velocity zone

100-200km depth under oceanic lithosphere where seismic waves velocities decrease due to 2% partial melt

Hot spot tracks (volcanoes and seamounts)

A hot spot is a stationary plume of hot material that rises to the surface where it melts at the base of the lithosphere due to lower pressure. The presence of seamounts and volcanoes suggests movement in the lithosphere over a hot spot.

What is a hot spot? List two examples of hot spots in the United States. How do they differ in terms of geologic environment?

A hot spot is a volcano that sits alone by itself and does not exist on a fault or boundary of a plate. Hawaii and

Which of the following about marine magnetic anomalies is/are FALSE? A. Alfred Wegener used marine magnetic anomalies to support his idea of Pangaea. B. The thicker a marine magnetic anomaly, the faster the spreading rate and/or the longer the duration of that polarity. C. A record of a normal polarity means that Earth's ancient magnetic field was parallel to Earth's current magnetic field. D. Earth's magnetic field is predictable and alternates on a regular basis, every 5 Ma (million years). E. Marine magnetic anomalies originate at trenches.

A. Alfred Wegener used marine magnetic anomalies to support his idea of Pangaea. D. Earth's magnetic field is predictable and alternates on a regular basis, every 5 Ma (million years). E. Marine magnetic anomalies originate at trenches.

The ______ of oceanic lithosphere INCREASES with distance from the mid-ocean ridges. A. density B. age C. thickness D. velocity E. temperature

A. density B. age

Which of the following could be likely characteristic(s) of a subduction zone? A. mountain ranges B. earthquakes C. rift zones D. transform faults E. hot spots

A. mountain ranges B. earthquakes C. rift zones

Discuss Alfred Wegner's contribution to the field of geology and how it laid the foundation for plate tectonics.

Alfred looked at the different continents on a map and realized that if you put the continents together, they would align and make one big supercontinent that he called Pangea. He gathered five different lines of evidence that would support this idea.

P-wave shadow zone

An area between 103 and 143 degrees from an earthquake focus where little P-wave energy is recorded by seismographs.

Arrange the ideas in sequential ordterm-29er from the first developed to the most recent. A. continental drift, plate tectonics, seafloor spreading B. continental drift, seafloor spreading, plate tectonics C. seafloor spreading, plate tectonics, continental drift D. seafloor spreading, continental drift, plate tectonics E. plate tectonics, seafloor spreading, continental drift

B. continental drift, seafloor spreading, plate tectonics

How do the properties of continental and oceanic crust affect isostasy? Explain how this is relevant to the distribution of ocean basins and the theory of plate tectonics.

Because the continental crust s thinker and less dense than the oceanic crust, it sits higher. This is relevant to plate tectonics because the crust is where tectonic plates sit and because they also sit on top of the plastic asthenosphere, they are able to move the way they do.

Why does oceanic crust always subduct at a subduction zone?

Because the oceanic crust is denser than continental crust, it will subduct instead of the continental one.

Earth's can be divided into compositional layers, which are from the surface to the deepest interior: A. core, mantle, oceanic crust, continental crust B. mantle, core, oceanic crust, continental crust C. continental crust, oceanic crust, mantle, core D. continental crust, mantle, core oceanic crust E. None of the above as they're all physical layers.

C. continental crust, oceanic crust, mantle, core

What are the two classification schemes used to partition Earth's layers.

Composition and physical state

1. How does seafloor spreading, and continental drift differ?

Continental drift is the concept, or the theory that Wegner came up with after realizing the continents could have formed one big supercontinent. Seafloor spreading is the explanation to the continental drift theory and why the continents eventually broke apart into smaller and separate continents.

Explain in detail how the following observations are explained by plate tectonics: b. Marine magnetic anomalies run parallel to and are symmetric about mid-oceanic ridges and alternate from normal to reverse polarities.

It supports the idea of plate tectonics because brings up the idea of convection which leads to a change in Earth's polarity. It supports the idea of convergent boundaries where lithospheric plates are essentially reused when they converge within one another.

What is a magnetic reversal? Where will magnetic north be during periods of normal and reverse polarities?

Magnetic reversal is when Earth's magnetic field flips and becomes the opposite of what a normal magnetic field would be. In a normal polarity, North is in our geologic north - the north pole. In reverse polarity, north would be in multiple places during the reversal but after, it would be in what we would consider south in a normal polarity.

Explain in detail how the following observations are explained by term-7plate tectonics: b. Marine magnetic anomalies run parallel to and are symmetric about mid-oceanic ridges and alternate from normal to reverse polarities.

Marine magnetic anomalies demonstrate how divergent boundaries and seafloor spreading are correlated. Younger, newer rock is located in the center of the ridge locking in the polarity of Earth and as you get farther away from the ridge the rock get older.

Explain in detail how the following observations are explained by plate tectonics: a. The presence of mid-ocean ridges, trenches, and marine magnetic anomalies. Define each.

Mid-ocean ridges are areas where plates spread and move older rock (oceanic crust) farther away from the spreading center moving continents apart as newer and hotter oceanic lithosphere is formed. Trenches are a sign of convergent boundaries where continental and oceanic plates meet and the subduction process takes place. Marine magnetic anomalies help are associated with mid-ocean ridges and seafloor spreading and record Earth's magnetic field when they were recorded by the rock. Since sediment thickness also increases as you go farther from the mid-ocean ridge, it helps us determine how old the seafloor is.

Explain the process by which Earth's magnetic field is recorded and preserved in the geologic record.

Mid-ocean ridges are key for this. Earth's magnetic field is recorded and preserved through the process of seafloor spreading. During this process, the hot and melted rock that is rich in iron cool with a magnetic polarity equivalent to that of Earth when it cooled.

What is the difference between relative and absolute plate motions?

Relative plate motion is the movement of a plate in respect to another plate while absolute plate motion is the movement of two plates relative to a fixed location in the mantle below the plates.

At a subduction zone, the denser plate—which is always oceanic lithosphere—will subduct.

T

The mantle is part of the lithosphere and the asthenosphere but is not a component of oceanic and continental crust.

T

The plate depicted in Q16 above moved west and then changed to south westly direction at ~2 Ma.

T

Why did the scientific community largely reject Wegener's ideas at the time? What paved the way for their later reexamination?

The scientific community did not accept Wegner's ideas at the time because he presented his theory without any explanation about how the continents would move. It wasn't until Marie Tharp found data points that would come up the same every time, they were plotted on an ocean ridge. Many scientists claimed to have explanations for these five lines of evidence.

s wave shadow zone

Those areas more than 103 degrees from an earthquake focus where no S-waves are recorded.

Where do transform boundaries form? Why? What is an example of a transform plate boundary in the continental United States?

Transform boundaries typically form at fracture zones between two ridge segments. An example of a transform boundary is the San Andreas fault.

Explain how we calculate current plate motions. Can this be used to determine past plate motions, why or why not. If not, describe how we determine the rate and direction plates have moved in the geologic past.

When trying to figure out the velocity of plate motion today, scientists measure the distance between the ridge axis and a location containing ocean floor of a specifiv age. We use the following equation to calculate the velocity: plate velocity = D/T (age of the seafloor) I think this can be used to determine past plate motion because we can determine how much a plate has moved from the ridge axis and how long it took for it to move as far as it did.

Explain what happens when two continental plates converge. What is a present-day example of a continental/continental collision zone? Describe the evolution from a subduction zone to a collisional boundary.

When two continental plates converge, collision happens because it is not dense enough to subduct. These new magma will likely rise and create volcanoes that erupt and build volcanic arcs of islands. The Peru-Chile trench is a present day example this.

Based on plate tectonics, explain how continents move laterally over time. Define and incorporate the following terms correctly in your explanation: mid-ocean ridges, spreading centers, trenches, subduction zones.

While divergent boundaries push older rock and oceanic crust outward and form a mid-ocean ridge, transform boundaries move continents laterally through a process called subduction. This happens when continental plates that are less dense and more rigid than meet oceanic plates, which are thinner and denser. The formation of ocean trenches follows where the rocks that have been pulled down begin to melt under the continent.

Explain the processes taking place to create a divergent plate boundary. How do continental rift zones and spreading ridges differ? Describe the evolution of a continental rift zone to a spreading ridge.

With divergent plate boundaries, plates are being pulled apart while forming new crust at mid-ocean ridges or spreading centers as well as continental rift zones. Continental rift zones take place on land or on continental lithosphere while spreading ridges take place on oceanic lithosphere (in the ocean). However, continental rift zones can develop into spreading ridges through time after a rift valley is formed where water can sit.

melting curve

varying degrees of melted material to the right of the curve; solid-state materials to the left the curve

refraction

when waves bend on a surface

reflection

when waves bounce off a surface