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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± ...
Oceanic: 5 - 10 km (3 - 6 mi) thick [5] and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro. The average thickness of the crust is about 15 - 20 km (9 - 12 mi). [6] Because both the continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle.
Here, is the thickness of the oceanic mantle lithosphere, is the thermal diffusivity (approximately 1.0 × 10 −6 m 2 /s or 6.5 × 10 −4 sq ft/min) for silicate rocks, and is the age of the given part of the lithosphere.
The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and is mafic-rich [9] (dense iron-magnesium silicate mineral or igneous rock). [10] The thicker crust is the continental crust, which is less dense [11] and is felsic-rich (igneous rocks rich in elements that form feldspar and quartz). [12]
Lithosphere–asthenosphere boundary. A diagram of the internal structure of Earth. The lithosphere consists of the crust and upper solid mantle (). The green dashed line marks the LAB. The lithosphere–asthenosphere boundary (referred to as the LAB by geophysicists) represents a mechanical difference between layers in Earth's inner structure.
Estimates of average thickness fall in the range from about 50 to 60 km. Most of this plagioclase-rich crust formed shortly after formation of the Moon, between about 4.5 and 4.3 billion years ago. Perhaps 10% or less of the crust consists of igneous rock added after the formation of the initial plagioclase-rich material.
Upper mantle. The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about 10 km (6.2 mi) under the oceans and about 35 km (22 mi) under the continents) and ends at the top of the lower mantle at 670 km (420 mi). Temperatures range from approximately 500 K (227 °C; 440 °F) at the ...
Oceanic crust is thin (~6 km thick) and dense (about 3.3 g/cm 3), consisting of basalt, gabbro, and peridotite. Consequently, most oceanic crust is subducted easily at an oceanic trench. In contrast, continental crust is thick (~45 km thick) and buoyant, composed mostly of granitic rocks (average density about 2.5 g/cm 3).