Ch 5
Correctly complete this sentence using the numbers provided
1
If a magnetic stripe is 120 km wide and formed over 4 m.y., what would the rate of seafloor spreading be?
30 km/m.y.
This diagram shows magnetic stripes on either side of the mid-ocean ridge. The number of different ages of stripes represented in this diagram is
6
If the area shown in this figure is 240 kilometers wide, and the oldest crust is 4 million years old, the approximate spreading rate is
60 kilometers per million years
On the accompanying figure, which letter is over the oldest oceanic crust?
A
Which area(s) on this world map is (are) likely to have volcanoes above sea level?
A
What is associated with reversed magnetic polarity?
A compass needle would point south
On the accompanying figure, which letter is likely over oceanic crust that is similar in age to that beneath letter E?
B
On this map of the south Atlantic, why is the mid-ocean ridge in the center of the ocean?
Seafloor is added to both sides during seafloor spreading
Select the statement that best describes how the process of plate tectonics circulates materials between the asthenosphere and the lithosphere
Some asthenosphere becomes lithosphere at mid-ocean spreading centers and reenters the asthenosphere at subduction zones
What causes magnetic stripes on the seafloor, such as those shown here?
Sometimes Earth's magnetic field points north and sometimes it points south
On a map showing the age of the seafloor, why are the patterns symmetrical in the Atlantic Ocean but not the Pacific Ocean?
Spreading along the Atlantic ridge added seafloor to plates on both sides, while subduction has consumed large areas of old oceanic crust in the Pacific
How is magma created in a subduction zone?
Subduction brings one plate to a depth hot enough for minerals to release water; this water causes melting in the overlying asthenosphere
Which way are the plates moving in this figure?
away from each other
The lithosphere consists of
both types of crust and the uppermost mantle
Intense geologic activity occurs at plate
boundaries
How fast do plates move relative to one another?
centimeters per year
Most oceanic plateaus are
constructed by volcanic eruptions probably over mantle plumes
Most oceanic islands and seamounts are
constructed by volcanic eruptions that first occur under water
The convergence of two continental masses is known as a(n)
continental collision
Why does the Tibetan Plateau have a high elevation?
continental collision
What type of plate boundary is depicted in this image?
continental rift
How did the Red Sea, shown between Arabia and Africa in this figure, form?
continental rifting followed by seafloor spreading
Some continents continue outward from the shoreline under shallow seawater, forming submerged benches called
continental shelves
Which of the following parts of the seafloor are the shallowest?
continental shelves
In what setting does the thickest sediment accumulate in the oceans?
continental shelves and slopes along passive margins
Island chains and seamounts cross parts of the ocean floor. These oceanic islands and associated seamounts are
different in character and origin from curved island arcs
Continental hot spots are typically marked by
high elevations, abundant volcanism, continental rifting
Magnetic patterns develop on the seafloor as basaltic lava erupts and cools, and
iron-rich minerals align with Earth's magnetic field
Which of the following features is associated with a deep oceanic trench?
island arc
A continent has an oceanic trench offshore of its coast. Which of the following is probably NOT present along this side of the continent?
melting along a mid-ocean ridge
A divergent plate boundary is most likely associated with a(n)
mid-ocean ridge
A n oceanic transform plate boundary is most likely associated with a(n)
mid-ocean ridge
What setting has the thinnest cover of sediment in the oceans?
mid-ocean ridges
The Earth's magnetic field is generated by
movement of iron and electrical currents within Earth's outer core
This figure shows a northwest-southeast line of islands and seamounts near Hawaii. If location 3 has the oldest rocks and Hawaii (1) has the youngest rocks, which way is the plate moving with respect to the hot spot?
northwest
This figure depicts what type of boundary?
ocean-continent convergent boundary
What occurs at mid-ocean ridges?
oceanic crust is created
What type of plate boundary is depicted in this figure?
oceanic divergent boundary
Cracks and steps that cross the seafloor and run at right angles to mid-ocean ridges are called
oceanic fracture zones
A convergent plate boundary is most likely associated with a(n)
oceanic trench
The deepest parts of the seafloor are
oceanic trenches
Harry Hess and Robert Dietz proposed that the oceanic crust in the Atlantic Ocean was spreading apart at the Mid-Atlantic Ridge and that this process moved the continents apart from one another. They called this process
seafloor spreading
A force that is important in driving plate tectonics is
slab pull, ridge push, hot spots
At mid-ocean ridges, as two plates diverge,
solid mantle in the asthenosphere rises toward the surface and begins to melt due to decompression
The process of one plate sliding beneath another plate is called
subduction
In this figure of Japan, what do the offshore trenches indicate?
subduction of oceanic crust
A region generally is higher than an adjacent region if ____________ than in the adjacent region
the crust is thicker
Hot spots form linear island chains because
the plate moves relative to the underlying hot spot
Which data were used to develop the hypothesis of continental drift?
the shape of the continents, the distribution of fossils, the distribution of glacial deposits and directions of glacial scratch marks
The main reason why the hypothesis of continental drift was not widely accepted was
there was no mechanism to move continents through the oceanic crust
