Spreading is believed to be caused by far-field stresses, and the upwelling of the mantle beneath the spreading axis is the passive response to plate separation. The Red Sea is an example of a new arm of the sea. As a result, the new sea will evaporate partially or completely several times before the elevation of the rift valley has been lowered to the point that the sea becomes stable.
As upwelling of magma continues, the plates continue to diverge, a process known as seafloor spreading. Includes photos of black smokers, tube worms, and equipment used by oceanographers.
The anomalously high values are considered to reflect the intrusion of molten material near the crests of the ridges. Supporting Evidence for Seafloor Spreading Abundant evidence supports the major contentions of the seafloor-spreading theory.
The magnetic history of the earth is thus recorded in the spreading ocean floors as in a very slow magnetic tape recording, forming a continuous record of the movement of the ocean floors.
Click the link for more information. In many locations, this mid-ocean ridge was found to contain a gigantic cleft, or rift, 20 to 30 mi 32—48 km wide and c.
This can result in an ever-widening seafloor at the expense of area lost elsewhere on the planet. Perhaps counter to expectation, the oceans are deeper closer to continents and farthest from midocean ridges.
The age-depth relation can be modeled by the cooling of a lithosphere plate   or mantle half-space in areas without significant subduction. The oceanic trenches bordering the continents mark regions where the oldest oceanic crust is reabsorbed into the mantle through steeply inclined, earthquake-prone subduction zones.
First proposed in the early s by the American geologist Harry H. Continued study of the mid-ocean ridges is a major component of U.
The Columbia Encyclopedia, 6th ed. At this point basaltic oceanic crust begins to form between the separating continental fragments. For younger children, omit explanation of magnetic stripes and reversals of polarity. In many locations, this mid-ocean ridge was found to contain a gigantic cleft, or rift, 20 to 30 mi 32—48 km wide and c.
Though first proposed by American geologist Frank Bursley Taylor in a lecture inthe first detailed theory of Since many plates, such as the North American Plate, include continental portions attached to oceanic portions, seafloor spreading also the direction in which continents move.
The idea that the seafloor itself moves and also carries the continents with it as it expands from a central axis was proposed by Harry Hess from Princeton University in the s. South America once fit into the area of the Niger Delta.
See also continental drift. The magmatism at the ridge is considered to be "passive upswelling", which is caused by the plates being pulled apart under the weight of their own slabs.
Copyright The Columbia University Press seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges.
First, samples of the deep ocean floor show that basaltic oceanic crust and overlying sediment become progressively younger as the mid-ocean ridge is approached, and the sediment cover is thinner near the ridge.
As the two active rifts continue to open, eventually the continental crust is attenuated as far as it will stretch. This zone consists of easily deformed rock and in some regions reaches a depth of km.
Second, the rock making up the ocean floor is considerably younger than the continents, with no samples found over million years old, as contrasted with maximum ages of over 3 billion years for the continental rocks.
The motivating force for seafloor spreading ridges is tectonic plate pull rather than magma pressure, although there is typically significant magma activity at spreading ridges. Earthguide at Scripps Institution of Oceanography Key points Seafloor spreading takes place at midocean ridges and produces basalt, the rock that makes up the oceanic crust.
How fast are plates moving apart at midocean ridges? Midocean ridges reach a typical summit elevation of 2, meters below sealevel. A spreading center includes a seismically active plate boundary zone a few kilometers to tens of kilometers wide, a crustal accretion zone within the boundary zone where the ocean crust is youngest, and an instantaneous plate boundary - a line within the crustal accretion zone demarcating the two separating plates.
BoxWashington, D. Seafloor spreading ends when midocean ridges are subducted. This confirms that older ocean crust has been reabsorbed in ocean trench systems.sea-floor spreading The theory that the ocean floor is created at the spreading (accretionary) plate margins within the ocean basins.
Igneous rocks rise along conduits from the mantle, giving rise to volcanic activity in a. If sea-floor spreading operates, the youngest oceanic crust should be found at the ridges and progressively older crust should be found in moving away from the ridges towards the continents.
This is the case. The oldest known ocean floor is dated at about million years, indicating that older ocean floor has been destroyed through subduction.
62 rows · Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other.
seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges.
First proposed in the early s by the A. Seafloor spreading is one of the two major processes of plate tectonics, the other being subduction. Seafloor spreading is the continuous process of forming new igneous rock at midocean ridges by injection of magma that forms new seafloor.
Seafloor spreading: Seafloor spreading, theory that oceanic crust forms along submarine mountain zones and spreads out laterally away from them.Download