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Concept
Earth's mantle
Summary
Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of and thus makes up 67% of the mass of Earth. It has a thickness of making up about 84% of Earth's volume. It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid, sometimes described as having the consistency of caramel. Partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle at subduction zones produces continental crust.
Earth's mantle is divided into two major rheological layers: the rigid lithosphere comprising the uppermost mantle, and the more ductile asthenosphere, separated by the lithosphere-asthenosphere boundary. Lithosphere underlying ocean crust has a thickness of around , whereas lithosphere underlying continental crust generally has a thickness of . The lithosphere and overlying crust make up tectonic plates, which move over the asthenosphere.
The Earth's mantle is divided into three major layers defined by sudden changes in seismic velocity:
the upper mantle (starting at the Moho, or base of the crust around downward to )
the transition zone (approximately ), in which wadsleyite (≈ ) and ringwoodite (≈ ) are stable
the lower mantle (approximately ), in which bridgmanite (≈ ) and post-perovskite (≈ ) are stable
The lower ~200 km of the lower mantle constitutes the D" (D-double-prime) layer, a region with anomalous seismic properties. This region also contains large low-shear-velocity provinces and ultra low velocity zones.
The top of the mantle is defined by a sudden increase in seismic velocity, which was first noted by Andrija Mohorovičić in 1909; this boundary is now referred to as the Mohorovičić discontinuity or "Moho".
The upper mantle is dominantly peridotite, composed primarily of variable proportions of the minerals olivine, clinopyroxene, orthopyroxene, and an aluminous phase. The aluminous phase is plagioclase in the uppermost mantle, then spinel, and then garnet below ~.
Official source
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