Wiki User
∙ 13y agoDecompression of the mantle produces magma, which is just molten rock. As the upper mantle (asthenosphere) moves closer to Earth's surface, it is under reduced pressure due to reduced depth. It does not get any warmer (in fact, it probably cools) but it melts.
The only reason the rest of the mantle is not molten is the pressure on it; solid rock is more dense than liquid rock, so even when it's above its melting point, it can be pressurized into a solid. Drop the pressure, and it expands into a liquid.
The same thing happens inside an auto radiator; pressure keeps the liquid coolant from expanding and turning into a gas (which does not absorb or transfer thermal energy from the engine well and will damage an engine). If you don't have a tight radiator cap or if you have a big leak in the system, your coolant easily boils.
The opposite happens with water; it expands to form a solid unlike most other materials. If you put pressure on it, you can push it back into a liquid even when it's below 0 degrees C. This is why you slip on ice, ice skates work well, and old snow sleds have just two thin metal runners. High pressure melts the ice and you slide on a thin layer of water.
Why is the magma mafic? It's due to content; being of low silica content it is low viscosity (runny) and will remain that way unless it passes through continental (felsic) lithosphere and picks up silica, thickening as it goes.
Wiki User
∙ 13y agoMelting points vary with pressure. In nearly all substances the melting point increases with increasing pressure. The peridotite in the mantle is extremely hot and under immense pressure. When it is decompressed some melting occurs. The composition is not uniform and some minerals have lower melting points than others. The mafic minerals will be able to melt while the ultramafic mineralls generally will not.
As the plates diverge, upper mantle rock rises and undergoes decompression melting along the rift. Because the upper mantle is comprised of mafic rock, the subsequent melt of this rock produces a mafic magma. Basalt and its coarse-grained intrusive twin, gabbro, are produced when this mafic magma solidifies.
decompression melting
Mafic magma has extremely high ferromagnesian content, produced by decompression melting. As the plates move apart, mantle rises to fill the void. As it melts, it forms mafic magma. Where plates are meeting, the compression of crust forms magma with higher silica content, thus forming felsic and intermediate magmas.
Is has Ultramafic rock in it, whereas core is made from Iron Alloy, Basically from metal
Melting points vary with pressure. In nearly all substances the melting point increases with increasing pressure. The peridotite in the mantle is extremely hot and under immense pressure. When it is decompressed some melting occurs. The composition is not uniform and some minerals have lower melting points than others. The mafic minerals will be able to melt while the ultramafic mineralls generally will not.
As the plates diverge, upper mantle rock rises and undergoes decompression melting along the rift. Because the upper mantle is comprised of mafic rock, the subsequent melt of this rock produces a mafic magma. Basalt and its coarse-grained intrusive twin, gabbro, are produced when this mafic magma solidifies.
The mantle is ultramafic.
decompression melting
Mafic magma has extremely high ferromagnesian content, produced by decompression melting. As the plates move apart, mantle rises to fill the void. As it melts, it forms mafic magma. Where plates are meeting, the compression of crust forms magma with higher silica content, thus forming felsic and intermediate magmas.
Mafic and ultramafic minerals, high in magnesium and iron.
Its made up of both. Oceanic crust is mostly mafic magma (basalt) and continental crust is mafic and felsic. The lithosphere also contains the upper portion of the upper mantle which is mostly mafic. The earths crust is 60% Si02 (silicates). Felsic rocks are much more silicate heavy than mafic. So one would assume that the crust is more felsic than mafic. That's just my conceptual thought process so don't take me on my word. Then again, the lithosphere also contains the upper mantle which is heavily mafic. So maybe the lithosphere in total is more mafic? Basically just typing thoughts down as they enter my brain. Answer I know for certain- Lithosphere is mafic and felsic.
Is has Ultramafic rock in it, whereas core is made from Iron Alloy, Basically from metal
No; granite is a felsic rock formed by either melting of contintal crust or extreme differentiation of more mafic magmas. The mantle is predominantly made up of an ultramafic rock known as peridotite.
The outer core of the earth is considered to be a liquid. The mantle is considered solid rock, but could be as much as 5% molten. The outer core is mostly iron and nickel, meanwhile the mantle is mostly ultra mafic rock. The outer core is hotter and more dense than the mantle.
Newly formed magmas are usually mafic.
Felsic rocks have 0-15% mafic crystals, while mafic rocks have 46-85% mafic crystals.