Continental Drift and Plate Tectonics Flashcards
- (tekto = to build) are those that deform Earth’s crust to create major structural features, such as mountains, continents, and ocean basins.
Tectonic processes
Wegener suggested that a single supercontinent named * consists all Earth’s landmasses once
Pangaea (“all lands”)
According to the plate tectonics model, the crust and
the uppermost part of the mantle constitute Earth’s strong outer layer, the *
lithosphere (lithos = stone).
Oceanic crust is composed of * and rich in dense iron and magnesium, whereas continental crust is composed largely of less dense * rocks.
basalt, granitic (mafic)
The * is a hotter, weaker region in the mantle that lies below the lithosphere
asthenosphere (asthenos = weak)
Although these rocks in asthenosphere are solid, they are quite *and respond to forces acting on them by exhibiting a slow * . By contrast, the comparatively cool and strong lithosphere tends to respond to forces acting on it by * . These differences result in Earth’s rigid outer shell being effectively detached from the underlying asthenosphere, which allows it to move independently of the layers below
ductile, fluid-like flow
bending or breaking
where two plates move
apart, resulting in upwelling and partial melting of
hot material from the mantle to create new seafloor
Divergent plate boundaries
where two plates move together, resulting either in oceanic lithosphere descending beneath an overriding plate, eventually to be reabsorbed into the mantle, or possibly in the collision of two continental blocks to createa mountain belt
Convergent plate boundaries
where two plates grind past each other without the production or destruction of lithosphere
Transform plate boundaries
Most divergent plate boundaries (di = apart, vergere =
to move) are located along the crests of * and can be thought of as constructive plate margins because this is where new ocean floor is generated
Two adjacent plates move away from each other,
producing long, narrow fractures in the ocean crust. As
a result, hot molten rock from the mantle below migrates upward to fill the voids left as the crust is being ripped apart.
oceanic ridges
Divergent plate boundaries are also called *
spreading centers.
- are elevated areas of the seafloor characterized by high heat flow and volcanism.
The * is the longest
topographic feature on Earth’s surface, exceeding
70,000 kilometers (43,000 miles) in length.
Oceanic ridges, global oceanic ridge system
any of several vast submarine regions that collectively cover nearly three-quarters of Earth’s surface. This includes the continental shelf, abyssal plain, mid-ocean ridge, etc.
Ocean basin
Further, along the crest of some ridge segments is a deep Canyon-like structure called a *
rift valley
The mechanism that operates along the oceanic ridge system to create new seafloor is appropriately called *
seafloor spreading.
Spreading typically averages around *
5 centimeters (2 inches) per year
As the tectonic forces continue to pull apart the crust,
the broken crustal fragments sink, generating an elongated depression called a
continental rift
where two plates move toward each other and the leading edge of one is bent downward as it slides beneath the other.
convergent plate boundaries
Convergent boundaries are also called * because they are sites where lithosphere is descending (being subducted) into the mantle.
subduction zones
- occurs because the density of the descending lithospheric plate is greater than the density of the underlying asthenosphere
Subduction
are long, linear depressions
in the seafloor that are generally located only a few hundred kilometers offshore of either a continent or a chain of volcanic islands such as the Aleutian chain
Deep-ocean trenches
At a depth of roughly 100 kilometers (60 miles), the wedge of mantle rock is sufficiently hot that the introduction of water from the slab below leads to some melting called * . Being less dense than the surrounding mantle, this hot mobile material gradually rises toward the surface. Depending on the environment, these mantle-derived masses of molten rock may ascend through the crust and give rise to a volcanic eruption. However, much of this material never reaches the surface but solidifies at depth—a process that thickens the crust.
partial melting
Where two oceanic slabs converge, one descends beneath the other, initiating volcanic activity by the same mechanism that operates at all subduction zones. The newly formed land, consisting of an arc-shaped chain of volcanic islands, is called a *
volcanic / island arc
One landmass moves toward the margin of another. Because of subduction of the intervening seafloor, the buoyancy of continental material inhibits it from being subducted. The result is the formation of a new * composed of deformed sedimentary and metamorphic rocks that often contain slivers of oceanic lithosphere
mountain belt
The subcontinent of * “rammed” into Asia, producing the * —the most spectacular mountain range on Earth
India, Himalayas
Along a * , plates slide horizontally past one another without the production or destruction of lithosphere.
transform plate boundary, also called a transform fault
Seafloor-spreading hypothesis predicted that the youngest oceanic crust would be found at the * , the site of seafloor production, and the oldest oceanic crust would be located * . Sediment thickness and age increases with * distance from the ridge
ridge crest, adjacent to the continents
increasing
are areas where heat and/or rocks in the mantle are rising towards the surface. The surface manifestation of this activity is a *, an area of volcanism, high heat flow, and crustal uplifting that is a few hundred kilometers across.
Mantle plumes, hot spot
Naturally occurring minerals are magnetic and are influenced by Earth’s magnetic field. One of the most common is the iron-rich mineral *, which is abundant in lava flows of * composition. The magnetite grains in molten lava are nonmagnetic. However, as the lava cools, these iron-rich grains become magnetized and align themselves in the direction of the existing magnetic lines of force.
magnetite, basaltic
During a * , the magnetic north pole becomes the magnetic south pole and vice versa. When rocks exhibit the same magnetism as the present magnetic field, they are said to possess * polarity, whereas rocks exhibiting the opposite magnetism are said to have * polarity.
magnetic reversal
normal, reverse
Earth has a * is because its solid iron core is surrounded by a fluid ocean of hot, liquid metal.
magnetic field
The flow of liquid iron in Earth’s core creates * , which in turn create the *
electric currents, magnetic field.
