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Decompression 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.
What else can I help you with?
Why would decompression of mantle peridotite cause the production of mafic magma?
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.
Mafic magma is generated at divergent boundaries because of?
Mafic magma is generated at divergent boundaries because of decompression melting caused by the upwelling of hot mantle material due to the pulling apart of tectonic plates. As the plates move away from each other, the decrease in pressure enables the mantle material to melt and form mafic magma.
Why are basalts produced on divergent plate boundaries?
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.
Why is the lava mostly mafic at divergent plate boundaries and intermediate and felsic at convergent plate boundaries?
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.
Does the mantle have mafic magma or felsic magma in it?
The mantle primarily contains mafic magma, which is rich in iron and magnesium. Felsic magma, which is rich in silica, is more commonly found in areas associated with continental crust or in volcanic arcs.
Why would decompression of mantle peridotite cause the production of mafic magma?
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.
Mafic magma is generated at divergent boundaries because of?
Mafic magma is generated at divergent boundaries because of decompression melting caused by the upwelling of hot mantle material due to the pulling apart of tectonic plates. As the plates move away from each other, the decrease in pressure enables the mantle material to melt and form mafic magma.
Why are basalts produced on divergent plate boundaries?
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.
Does the mantle have mafic or felsic in it?
The mantle is ultramafic.
Why is the lava mostly mafic at divergent plate boundaries and intermediate and felsic at convergent plate boundaries?
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.
What is the mantle rich in?
Mafic and ultramafic minerals, high in magnesium and iron.
Does the mantle have mafic magma or felsic magma in it?
The mantle primarily contains mafic magma, which is rich in iron and magnesium. Felsic magma, which is rich in silica, is more commonly found in areas associated with continental crust or in volcanic arcs.
What is the lithosphere made of mafic or felsic?
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.
What kind of igneous rock is mafic and formed deep in the ground?
A mafic igneous rock formed deep within the Earth's crust is typically basalt. Basalt is fine-grained and rich in minerals like pyroxene, olivine, and plagioclase. It commonly forms from the solidification of magma that has originated from the mantle.
Why are xenoliths mafic minerals?
Xenoliths are often mafic minerals because they originate from the Earth's mantle, which is composed of mafic rocks such as basalt and gabbro. These minerals are more likely to survive the extreme conditions of volcanic eruptions, which is how xenoliths are transported to the Earth's surface. Additionally, mafic minerals have higher melting points compared to felsic minerals, making them more resistant to being melted and destroyed during volcanic processes.
How do mafic volcanic rocks get to Earth's surface?
Mafic volcanic rocks reach the Earth's surface through volcanic eruptions. These rocks originate from the mantle and are rich in magnesium and iron. When magma containing mafic composition rises to the surface, it can erupt as lava and form volcanic landforms like shield volcanoes or basalt flows.
What does the Earth's mantle mostly contain?
The Earth's mantle mostly contains solid rock composed of silicate minerals rich in magnesium and iron. It is made up of ultramafic and mafic rocks such as peridotite and pyroxenite. The mantle is a key layer of the Earth's structure located between the crust and the core.
