What Happens to Older Oceanic Crust as New Rock Is Formed During Seafloor Spreading

Seafloor spreading and other tectonic action processes are the outcome of mantle convection. Mantle convection is the tedious, churning motility of Globe'southward mantle. Convection currents comport heat from the lower mantle and cadre to the lithosphere. Convection currents also "recycle" lithospheric materials dorsum to the mantle.

Seafloor spreading occurs at divergent plate boundaries. Every bit tectonic plates slowly motion abroad from each other, heat from the drapery'southward convection currents makes the crust more plastic and less dumbo. The less-dumbo fabric rises, frequently forming a mount or elevated expanse of the seafloor.

Somewhen, the crust cracks. Hot magma fueled by mantle convection bubbles upward to make full these fractures and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This rock (basalt) becomes a new office of Globe's chaff.

Mid-Body of water Ridges

Seafloor spreading occurs forth mid-bounding main ridges—large mountain ranges rising from the ocean flooring. The Mid-Atlantic Ridge, for instance, separates the Due north American plate from the Eurasian plate, and the Due south American plate from the African plate. The East Pacific Rising is a mid-ocean ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the Due north American plate, the Cocos plate, the Nazca plate, and the Antarctic plate. The Southeast Indian Ridge marks where the southern Indo-Australian plate forms a divergent boundary with the Antarctic plate.

Seafloor spreading is not consequent at all mid-ocean ridges. Slowly spreading ridges are the sites of tall, narrow underwater cliffs and mountains. Quickly spreading ridges have a much more gentle slopes.

The Mid-Atlantic Ridge, for instance, is a slow spreading center. It spreads 2-5 centimeters (.eight-2 inches) every year and forms an body of water trench about the size of the One thousand Canyon. The East Pacific Rise, on the other mitt, is a fast spreading center. It spreads virtually half dozen-16 centimeters (3-6 inches) every yr. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for ane to develop!

The newest, thinnest crust on Earth is located about the center of mid-ocean ridge—the bodily site of seafloor spreading. The age, density, and thickness of oceanic chaff increases with distance from the mid-ocean ridge.

Geomagnetic Reversals

The magnetism of mid-ocean ridges helped scientists first identify the process of seafloor spreading in the early 20th century. Basalt, the once-molten rock that makes upward most new oceanic crust, is a adequately magnetic substance, and scientists began using magnetometers to mensurate the magnetism of the ocean floor in the 1950s. What they discovered was that the magnetism of the ocean floor around mid-ocean ridges was divided into matching "stripes" on either side of the ridge. The specific magnetism of basalt stone is adamant by the Earth's magnetic field when the magma is cooling.

Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-ocean ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern.

Geographic Features

Oceanic chaff slowly moves away from mid-sea ridges and sites of seafloor spreading. As it moves, information technology becomes cooler, more dense, and more than thick. Eventually, older oceanic chaff encounters a tectonic purlieus with continental crust.

In some cases, oceanic chaff encounters an agile plate margin. An agile plate margin is an actual plate purlieus, where oceanic crust and continental chaff crash into each other. Active plate margins are often the site of earthquakes and volcanoes. Oceanic chaff created by seafloor spreading in the Eastward Pacific Rise, for example, may become part of the Ring of Fire, the horseshoe-shaped pattern of volcanoes and earthquake zones around the Pacific bounding main basin.

In other cases, oceanic crust encounters a passive plate margin. Passive margins are not plate boundaries, but areas where a single tectonic plate transitions from oceanic lithosphere to continental lithosphere. Passive margins are not sites of faults or subduction zones. Thick layers of sediment overlay the transitional chaff of a passive margin. The oceanic crust of the Mid-Atlantic Ridge, for example, will either become part of the passive margin on the North American plate (on the due east coast of N America) or the Eurasian plate (on the west coast of Europe).

New geographic features tin can be created through seafloor spreading. The Ruby-red Sea, for case, was created every bit the African plate and the Arabian plate tore abroad from each other. Today, only the Sinai Peninsula connects the Eye Due east (Asia) with Northward Africa. Eventually, geologists predict, seafloor spreading volition completely carve up the 2 continents—and join the Ruby and Mediterranean Seas.

Mid-body of water ridges and seafloor spreading can also influence sea levels. Every bit oceanic crust moves away from the shallow mid-ocean ridges, it cools and sinks as information technology becomes more dense. This increases the book of the ocean basin and decreases the body of water level. For example, a mid-sea ridge system in Panthalassa—an ancient bounding main that surrounded the supercontinent Pangaea—contributed to shallower oceans and higher sea levels in the Paleozoic era. Panthalassa was an early form of the Pacific Ocean, which today experiences less seafloor spreading and has a much less extensive mid-sea ridge system. This helps explain why sea levels have fallen dramatically over the past fourscore million years.

Seafloor spreading disproves an early on part of the theory of continental migrate. Supporters of continental drift originally theorized that the continents moved (drifted) through unmoving oceans. Seafloor spreading proves that the ocean itself is a site of tectonic action.

Keeping Earth in Shape

Seafloor spreading is just one part of plate tectonics. Subduction is some other. Subduction happens where tectonic plates crash into each other instead of spreading apart. At subduction zones, the edge of the denser plate subducts, or slides, below the less-dense one. The denser lithospheric material and so melts back into the World'south mantle.

Seafloor spreading creates new crust. Subduction destroys old crust. The two forces roughly balance each other, so the shape and diameter of the Earth remain abiding.

Earth's newest crust is created at sites of seafloor spreading—ruddy sites on this map.

Map courtesy NOAA

Triple Junctions

Seafloor spreading and rift valleys are common features at "triple junctions." Triple junctions are the intersection of iii divergent plate boundaries. The triple junction is the central point where three cracks (boundaries) split off at virtually 120° angles from each other.

In the Afar Triple Junction, the African, Somali, and Arabian plates are splitting from each other. The Slap-up Rift Valley and Blood-red Sea (a major site of seafloor spreading) are the effect of plate tectonics in the Afar Triple Junction.

active plate margin

Noun

convergent tectonic plate boundary where an oceanic plate is crashing into a continental plate.

basalt

Noun

type of dark volcanic rock.

churn

Verb

to mix vigorously or violently.

Substantive

steep wall of stone, earth, or ice.

consequent

Describing word

maintaining a steady, reliable quality.

Noun

i of the seven main state masses on World.

continental chaff

Noun

thick layer of World that sits beneath continents.

Noun

the motility of continents resulting from the motility of tectonic plates.

convection current

Noun

movement of a fluid from a cool area to a warm area.

Substantive

the extremely hot center of Globe, some other planet, or a star.

Noun

rocky outermost layer of Earth or other planet.

dense

Describing word

having parts or molecules that are packed closely together.

diameter

Noun

width of a circle.

disprove

Verb

to testify incorrect.

divergent boundary

Noun

area where two or more tectonic plates are moving away from each other. Also called an extensional boundary.

convulsion

Noun

the sudden shaking of Earth'southward chaff caused past the release of energy along mistake lines or from volcanic activity.

fast spreading middle

Noun

mid-body of water ridge where seafloor spreading is occuring at more than 100 millimeters (iv inches) a year.

fault

Noun

a crack in the Earth'south crust where there has been move.

frigid

Adjective

very cold.

geologic

Describing word

having to practice with the physical formations of the World.

geologist

Noun

person who studies the concrete formations of the Earth.

Noun

rock formed past the cooling of magma or lava.

Noun

outer, solid portion of the Earth. Also called the geosphere.

Noun

molten, or partially melted, rock beneath the Earth's surface.

magnetic field

Noun

surface area effectually and affected by a magnet or charged particle.

Noun

force by which objects attract or repel one another.

magnetometer

Noun

scientific instrument used to measure the presence, strength, and management of World'due south magnetic field.

Noun

middle layer of the Globe, made of mostly solid rock.

mantle convection

Substantive

slow movement of Earth'due south solid curtain caused by convection currents transferring heat from the interior of the Earth to the surface.

Mid-Atlantic Ridge

Noun

underwater mount range that runs from Iceland to Antarctica.

mid-ocean ridge

Noun

underwater mountain range.

molten

Adjective

solid material turned to liquid by heat.

mountain range

Substantive

serial or chain of mountains that are shut together.

ocean basin

Noun

depression in the Earth's surface located entirely below the sea.

oceanic crust

Noun

sparse layer of the Earth that sits beneath ocean basins.

Substantive

a long, deep depression in the body of water floor.

Paleozoic Era

Noun

about 541-252 one thousand thousand years agone.

Pangaea

Noun

supercontinent of all the Earth'due south landmass that existed about 250 one thousand thousand years ago.

passive plate margin

Noun

lithospheric region where oceanic crust transitions to continental chaff without faults or subduction zones.

plastic

Noun

chemical material that tin be hands shaped when heated to a loftier temperature.

Noun

move and interaction of the Earth's plates.

predict

Verb

to know the upshot of a situation in advance.

Substantive

low in the ground acquired by the World'southward chaff spreading apart.

Noun

horseshoe-shaped string of volcanoes and convulsion sites around edges of the Pacific Ocean.

Noun

rift in underwater mountain range where new oceanic crust is formed.

Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-twelvemonth bicycle.

seawater

Substantive

salty water from an ocean or sea.

Noun

solid material transported and deposited by h2o, ice, and wind.

slow spreading centre

Substantive

mid-bounding main ridge where seafloor spreading is occuring at less than 55 millimeters (two inches) a year.

subduct

Verb

to pull downwardly or beneath something.

subduction zone

Noun

area where one tectonic plate slides under another.

supercontinent

Noun

ancient, giant landmass that split apart to form all the continents we know today.

symmetrical

Adjective

having the same arrangement of parts on either side.

tectonic action

Noun

motility of tectonic plates resulting in geologic activity such every bit volcanic eruptions and earthquakes.

tectonic plate

Noun

massive slab of solid rock made upwardly of Globe's lithosphere (chaff and upper pall). Also called lithospheric plate.

theorize

Verb

to formulate and propose a group of ideas to explicate a scientific question.

transition

Noun

movement from ane position to another.

transitional crust

Noun

lithospheric region where oceanic chaff transitions into continental crust.

Substantive

an opening in the Earth'due south crust, through which lava, ash, and gases erupt, and also the cone congenital by eruptions.

volume

Noun

space an object occupies.

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Source: https://www.nationalgeographic.org/encyclopedia/seafloor-spreading/

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