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The Pacific Ocean is also an active, shrinking oceanic basin, even though it has both spreading ridge and oceanic trenches. Perhaps the best example of an inactive oceanic basin is the Gulf of Mexico, which formed in Jurassic times and has been doing nothing but collecting sediments since then. [15] The Aleutian Basin is another example of a ...
The mantle within about 200 km (120 mi) above the core–mantle boundary appears to have distinctly different seismic properties than the mantle at slightly shallower depths; this unusual mantle region just above the core is called D″ ("D double-prime"), a nomenclature introduced over 50 years ago by the geophysicist Keith Bullen. [26]
The youngest oceanic rocks are at the oceanic ridges, and they get progressively older away from the ridges. [17] As the mantle rises it cools and melts, as the pressure decreases and it crosses the solidus. The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7± ...
Beneath oceanic crust, the LAB ranges anywhere from 50 to 140 km in depth, except close to mid-ocean ridges where the LAB is no deeper than the depth of the new crust being created. [10] Seismic evidence shows that oceanic plates do thicken with age. This suggests that the LAB underneath oceanic lithosphere also deepens with plate age.
New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 170 million years old, while parts of the continental lithosphere are billions of years old. [12] [13]
Because the ocean floors are mainly sima, it is also sometimes called the 'oceanic crust'. The name 'sima' was taken from the first two letters of silica and of magnesia . Comparable is the term sial (another antiquated blended term), [ 2 ] which is the name for the upper layer of Earth's crust ( continental crust ) , namely rocks rich in ...
Scientists using an ocean drilling vessel have dug the deepest hole ever in rock from Earth's mantle - penetrating 4,160 feet (1,268 meters) below the Atlantic seabed - and obtained a large sample ...
The transition zone is located between the upper mantle and the lower mantle between a depth of 410 km (250 mi) and 670 km (420 mi).. This is thought to occur as a result of the rearrangement of grains in olivine to form a denser crystal structure as a result of the increase in pressure with increasing depth. [6]