What is Obduction zone? Obduction . Obduction occurs where a fragment of continental crust is caught in a subduction zone with resulting overthrusting of oceanic mafic and ultramafic rocks from the mantle onto the continental crust.
What is a subduction zone?
A subduction zone is something that happens only with convergent boundaries. Subduction is where, after colliding, one plate sinks below the other. And a subduction zone is the area where two plates are sandwiched on top of each other, like a tectonic BLT. Are you a student or a teacher?
What is Obduction and where does it occur?
Obduction often occurs where a small tectonic plate is caught between two larger plates, with the crust (both island arc and oceanic) welding onto an adjacent continent as a new terrane.
What is the meaning of oceanic-oceanic obduction?
The overthrusting of oceanic lithosphere onto continental lithosphere at a convergent plate boundary. Obduction was originally defined by Coleman to mean the overthrusting of oceanic lithosphere onto continental lithosphere at a convergent plate boundary where continental lithosphere is being subducted beneath oceanic lithosphere.
What type of plate boundary does obduction occur?
Obduction occurs where a fragment of continental crust is caught in a subduction zone with resulting overthrusting of oceanic mafic and ultramafic rocks from the mantle onto the continental crust. Obduction often occurs where a small tectonic plate is caught between two larger plates, with the crust (both island arc and oceanic)...
What is the subduction zone of an ocean?
subduction zone, oceanic trench area marginal to a continent in which, according to the theory of plate tectonics, older and denser seafloor underthrusts the continental mass, dragging downward into the Earth's upper mantle the accumulated trench sediments.
How does a subduction zone work?
These plates collide, slide past, and move apart from each other. Where they collide and one plate is thrust beneath another (a subduction zone), the most powerful earthquakes, tsunamis, volcanic eruptions, and landslides occur.
What is evidence of a subduction zone?
Scientists typically search for structural or geophysical indications that offer telltale signals of the locations of past subduction zones. Such visible evidence might include old fault planes preserved in rock or subsurface images (afforded by seismic data) of former plates now swallowed by the mantle.
Why are subduction zones important?
The primary subduction zone we study is the Cascadia Subduction Zone, where the Juan de Fuca Plate is sliding beneath the North American Plate. That subduction zone is largely responsible for the Cascade Volcanic Range, as well as significant earthquake and tsunami hazard for the Pacific Northwest.
Why do subduction zones cause earthquakes?
Subduction zones are plate tectonic boundaries where two plates converge, and one plate is thrust beneath the other. This process results in geohazards, such as earthquakes and volcanoes.
What are the 3 types of subduction zones?
There are three main types: Convergent boundaries, where plates move towards each other. Divergent boundaries, where plates move apart. Transform boundaries, where plates slide alongside each other.
Which islands formed from subduction zones?
An example of a series of islands that formed from a genuine subduction zone is the Aleutian Islands, positioned near the border between two oceanic plates. Another example of a subduction zone would be the one that formed the Cascade Volcanoes in Oregon, Washington, and Western Canada.
What are the three types of plate boundaries?
There are three types of plate boundaries: convergent, divergent and transform. Convergent boundaries are where two plates are moving towards each other, and this is where subduction zones can be created.
What happens when an oceanic plate collides with a continental plate?
When an oceanic plate collides with a continental plate, the oceanic plate (denser) subducts beneath the continental plate (less dense). The result of this is a trench under the sea on the oceanic side and volcanoes or mountains on the continental side.
What are the features of the oceanic and continental plates?
Features include an underwater trench on the oceanic side and mountains on the continental side. When two continental plates meet, the main feature that results is mountains. The Himalayas, the biggest mountain range in the world, was formed this way. Two oceanic plates collide to create large underwater trenches.
What is the crust of an oceanic plate?
Instead, an oceanic plate is a section of the Earth's crust that's made mostly of mafic or basaltic rock.
What happens when two tectonic plates collide?
When two huge tectonic plates collide, the pressure and friction is great enough that the material in the Earth's mantle can melt, and both earthquakes and volcanoes can result. The exact features around a subduction zone depend on the type of tectonic plates that are colliding.
Where are subduction zones located?
Subduction zones occur all around the edge of the Pacific Ocean, offshore of Washington, Canada, Alaska, Russia, Japan and Indonesia. Called the "Ring of Fire," these subduction zones are responsible for the world's biggest earthquakes, the most terrible tsunamis and some of the worst volcanic eruptions.
When was the first subduction zone discovered?
Scientists first identified subduction zones in the 1960s, by locating earthquakes in the descending crust.
What is the link between subduction zones and volcanoes?
Inland of each subduction zone is a chain of spouting volcanoes called a volcanic arc , such as Alaska's Aleutian Islands. The Toba volcanic eruption in Indonesia, the largest volcanic eruption in the past 25 million years, was from a subduction zone volcano.
Which type of plate can transport both continental and oceanic crust?
Tectonic plates can transport both continental crust and oceanic crust, or they may be made of only one kind of crust. Oceanic crust is denser than continental crust. At a subduction zone, the oceanic crust usually sinks into the mantle beneath lighter continental crust. (Sometimes, oceanic crust may grow so old and that dense ...
Why is the Cascadia subduction zone the largest?
The main reason is size. The size of an earthquake is related to the size of the fault that causes it, and subduction zone faults are the longest and widest in the world. The Cascadia subduction zone offshore of Washington is about 620 miles (1,000 kilometers) long and about 62 miles (100 km) wide.
How far does the Earth's sinking slab bend?
The quakes reveal that the sinking slab tends to bend at an angle between 25 to 45 degrees from Earth's surface, though some are flatter or steeper than this.
Can a subduction zone earthquake cause a tsunami?
For earthquakes larger than a magnitude 7.5, this can cause a tsunami, a giant sea wave, by suddenly moving the seafloor. However, not all subduction zone earthquakes will cause tsunamis. Also, some earthquakes trigger tsunamis by sparking underwater landslides.
Subduction
When tectonic plates converge, one plate slides beneath the other plate, or subducts, descending into the Earth’s mantle at rates of 2-8 centimeters (1–3 inches) per year.
Giant Earthquakes
At shallow depths, less than about 25 kilometers (16 miles), the interface between the plates may become stuck, or “locked,” and stresses build along these giant "megathrust" faults. Eventually stresses exceed the fault’s strength and it breaks free, releasing the stored energy as seismic (shaking) waves in an earthquake.
Other More Frequent Smaller Earthquakes
Earthquakes occur elsewhere in subduction zones, within the subducting plate (“intra-plate”) that often are deeper than about 30 kilometers (19 miles) below the surface, or at the “outer-rise” just a few kilometers below the surface where the plate begins its descent. They also occur within the crust of the upper plate, often just beneath our feet.
Inundating Tsunamis
When the surface of the seafloor moves vertically, a tsunami is born. This can happen either when earthquake faults move vertically just below the surface, or when submarine landslides transport large masses.
Land-level Changes over Vast Areas
In the hundreds of years between megathrust earthquakes, the squeezing motions cause the upper plate to bulge and uplift just above and inboard of the locked region, over thousands of square kilometers.
Abundant Landslides
Landslides are particularly abundant in subduction zones, where geologic processes create steep rapidly evolving topography. Onshore, high rates of rainfall on the seaward side of the mountain chains created by the squeezing of the plates makes landslides more probable. Offshore, thick sediments pile up, creating steep unstable slopes.
More Educational Resources
The Earth’s many tectonic plates can be thousands of miles across and underlie both continents and oceans. These plates collide, slide past, and move apart from each other. Where they collide and one plate is thrust beneath another (a subduction zone), the most powerful earthquakes, tsunamis, volcanic eruptions, and landslides occur.
What Is a Subduction Zone?
The earth is made of multiple plates that move relative to each other on the surface of the Earth. There are three main types of tectonic plate boundaries and interactions.
Tectonic Plate Boundaries
Plate tectonic theory states that the Earth's lithosphere, which is its uppermost layer consisting of the crust and uppermost rigid mantle, is broken up into massive plates that move relative to each other on the surface. Their motion is driven by convection currents within the mantle asthenosphere, which is the upper mantle that behaves fluidly.
Subduction Zone: True or False Activity
This activity will help assess your knowledge of the definition, location, and examples of subduction zones.
What are the two parallel mountain ranges that form the Cascadia Subduction Zone in the Pacific Northwest?
The Coast Range and Cascades are the two parallel mountain ranges that form the Cascadia Subduction Zone in the Pacific Northwest. The forearc basin is the Willamette Valley in Oregon and Puget Sound in Washington.
What is the result of the subduction of the Juan de Fuca Plate?
Subduction of the Juan de Fuca Plate results in the formation of the Coastal Ranges and Cascade Volcanoes, as well as a variety of earthquakes, in the Pacific Northwest. Olympic and Mt. Rainier national parks showcase the contrasting landscapes of the two parallel mountain ranges.
What type of crust forms when a plate with thinner (less buoyant) oceanic crust descends beneath a
Subduction zones form where a plate with thinner (less-buoyant) oceanic crust descends beneath a plate with thicker (more-buoyant) continental crust. Two parallel mountain ranges commonly develop above such a subduction zone – a coastal range consisting of sedimentary strata and hard rock lifted out of the sea ( accretionary wedge ), and a volcanic range farther inland ( volcanic arc ). Ancient magma chamber rocks can be exposed if subduction stops and the volcanoes erode away.
Which plate boundary formed between the Pacific and Pacific plates?
As the mid-ocean ridge separating the Farallon and Pacific Plates entered the subduction zone, the Farallon Plate separated into the Juan de Fuca and Cocos Plates. A transform plate boundary developed where the Pacific Plate was in contact with the North American Plate and the volcanism ceased in central California.
Summary
Obduction is a geological process whereby denser oceanic crust (and even upper mantle) is scraped off a descending ocean plate at a convergent plate boundary and thrust on top of an adjacent plate. When oceanic and continental plates converge, normally the denser oceanic crust sinks under the continental crust in the process of subduction. Obduction, which is less common, normally occurs …
Formation
Discovery
Quotes
Setting
Mechanism
- Where two tectonic plates meet at a subduction zone, one bends and slides underneath the other, curving down into the mantle. (The mantle is the hotter layer under the crust.) Tectonic plates can transport both continental crust and oceanic crust, or they may be made of only one kind of crust. Oceanic crust is denser than continental crust. At a subduction zone, the oceanic crust usually s…
Risks
- Scientists first identified subduction zones in the 1960s, by locating earthquakes in the descending crust. Now, new instruments can precisely track the shifting tectonic plates.
Effects
- \"We can see very clear pictures of how the plates move, mostly due to GPS data,\" said Vasily Titov, director of National Oceanic and Atmospheric Administration's Center for Tsunami Research in Seattle, Washington. \"Subduction zones are huge boundaries, so they generate very large earthquakes,\" Titov told Live Science.
Impact
- Subduction zones occur all around the edge of the Pacific Ocean, offshore of Washington, Canada, Alaska, Russia, Japan and Indonesia. Called the \"Ring of Fire,\" these subduction zones are responsible for the world's biggest earthquakes, the most terrible tsunamis and some of the worst volcanic eruptions.
Geology
- Shoving two massive slices of Earth's crust together is like rubbing two pieces of sandpaper against each other. The crust sticks in some places, storing up energy that is released in earthquakes. The massive scale of subduction zones means they can cause enormous earthquakes. The largest earthquakes ever recorded were on subduction zones, such as a magn…