Lesson 27: Chapter 27 Continental Drift and Plate Tectonics

Which of the following is a main function of a transform boundary? A. To connect a divergent and convergent boundary B. To connect segments of a spreading center ridge C. To provide a means for subduction to occur D. To release pressure built up from mantle plume activity

to connect segments of a spreading center ridge

What type of landforms would you expect to find at this plate boundary? (Mark all that apply.) A. Trench B. Linear island chain C. Oceanic ridge D. Island arc E. Fold mountain belt

trench, island arc

The above picture shows the plates in the northern hemisphere. The Mid-Atlantic ridge runs down the middle of the Atlantic Ocean. What direction is the North American plate moving relative to the Eurasian plate? A. North B. South C. East D. West

west

Convergent Plate Boundaries

- boundaries where two plates are colliding with each other - three types: ocean to ocean, ocean to continent, and continent to continent

Transform Plate Boundaries

- boundaries where two plates are sliding past each other - comment other types of boundaries (ridge to ridge, trench to trench, and ridge to trench) - commonly found connecting different pieces of divergent plate boundaries - severe earthquakes are common - small gradual plate movements also common

Oceanic Rifts

- characterized by a central first valley and abyssal hills on either side of the valley - eventually sediment covers the abyssal hills to form abyssal plains - earthquakes frequent but shallow and mild

Continental Rifts

- earthquakes common, severe, and shallow - volcanoes occur - if it continues a sea will form between the two fragments - the sea can become an ocean

Ridge Push

- helps move Earth's plates - the ridge is high and have gravitational potential energy that is converted into kinetic energy as the plate moves - result of the oceanic ridges being topographically elevated - gravity then causes them to slide "downhill"

Slab Pull

- helps move the tectonic plates - as an oceanic plate becomes old, cold, and dense it sinks back into the mangle, pulling the rest o the plate along with it - tug of the slab that is going down under another slab into the asthenosphere

Continental-Continental Plate Boundary

- subduction stops - form folded mountain belts - earthquakes are severe but fairly shallow and common - volcanoes don't usually form - two pieces are welded together (continent larger than before)

Plate Tectonics Model

- the surface of the Earth is broken into lithospheric plates - these plates rest/float on mushy, semi-liquid weak asthenosphere - the boundaries are marked by earthquakes - plates move due to gravitational and electromagnetic forces

Oceanic-Continental Convergent Plate Boundary

- trench forms - water released and causes volcanic mountain chain (volcanoes more explosive) - matter from the oceanic plate that isn't subducted is scraped onto the continental side - earthquakes are frequent and severe but vary in depth

Oceanic-Oceanic Convergent Plate Boundary

- trench forms as the older, cooler, and more dense oceanic slab is subducted - subducted plate releases water and heated up causing volcanoes to form - forms island arcs - earthquakes are frequent and severe

Hot Spots

- volcanoes that result from lithosphere moving over a mantle plume - Hawaii - as plate moves over the mantle a line of volcanic structures masks the passage

The picture below shows the plates. The Cascade mountain range, famous for its volcanoes, is found on the west coast of North America. What direction is the Juan De Fuca plate moving assuming that the North American Plate is stationary? A. North B. South C. East D. West E. It is not moving.

east

Which of the following features are most commonly associated with converging plate boundaries between two continental plates? A. Oceanic ridges B. Island arcs C. Fold mountain belts D. Hotspots E. More than one of the above

fold mountain belts

What type of earthquakes would you expect to find here? A. Infrequent, mild, and shallow B. Frequent, mild, and shallow C. Frequent, severe, and shallow D. Frequent, severe, and varying in depth from shallow to deep E. Infrequent, mild, and varying in depth from shallow to deep

frequent, severe, and varying in depth from shallow to deep

A divergent plate margin runs between Antartica and South America. What will happen as a result? A. The South Atlantic will shrink. B. Folded mountains will soon begin to emerge as islands between the two continents. C. The ocean seperating them will grow wider. D. A deep ocean trench will form and grow between the two continents. E. Volcanic island arcs will emerge between the two continents.

the ocean separating them will grow wider

Based upon the geologic map, what plate is being subducted? A. the northwest plate B. the southeast plate

the southeast plate

Divergent Plate Boundaries

- boundaries were two plates are splitting apart from each other - two types: oceanic rifts and congenital rifts

What is the evidence behind pangea?

1. jigsaw fit of the continents 2. structural trends of the continents when the continents are put back together 3. paleontological (fossil) evidence 4. paleoclimatic evidence (glaciers) 5. paleomagnetic evidence

The rock that makes up the ocean floor has alternating bands where the magnetic field points north, then south. What is the significance of these bands. A. The reverse polarity (south) bands are all older than the normal polarity (north) bands, giving alternating stripes of young and old rock. B. The bands occur symmetrically to each side of the ridge where new ocean crust is slowly being made. The Earth's magnetic field flips, and the field in the basalt points the same direction as the Earth's field when the rock formed. C. As rocks age, their magnetic fields change directions, so measuring the strength and direction of the magnetic field in the basalt allows us to accurately date the age of the rock. D. The magnetic field indicates the direction that the plate was moving. Alternating bands prove that the ocean alternately spreads and closes. E. The bands only occur in regions where the ocean crust is coming together to form a ridge, and temperatures and pressures are high enough to force the magnetic field in the rocks to change direction

The bands occur symmetrically to each side of the ridge where new ocean crust is slowly being made. The Earth's magnetic field flips, and the field in the basalt points the same direction as the Earth's field when the rock formed.

The picture above shows the western part of North America. Some geologists believe that a continental rift zone is forming between Baja California and the rest of North America. If this rift zone were to continue, what would be the eventual result in this region and the Gulf of California? A. Fold mountain belts B. New ocean C. Trench D. Island arcs E. Linear island chain

new ocean

(look at slides for pic - you didn't do good on these so review!) What type of plate boundary is represented by this area? A. Oceanic rift B. Continental rift C. Oceanic-oceanic convergent zone D. Oceanic-continental convergent zone E. Continental-continent convergent zone F. Transform fault

oceanic-oceanic convergent zone

How does the plate tectonic model account for the movement of continents? A. The continents float on the surface of the liquid core of the earth. B. The continents move/cut through the rock of the lithosphere, albeit very slowly. C. The continents rest on rigid plates. The plates sit on a "mushy" layer which allows them to slide and move. D. The continents have a layer of liquid rock underneath them that allows them to slide over the ocean crust. E. Plate tectonics is unable to explain continental drift.

the continents rest on rigid plates, the plates sit on a "mushy" layer which allows them to slide and move