Why does water induce melting in a subduction zone quizlet?
Water-induced melting occurs when water is added to rocks in order to lower the melting temperatures. This happens in subduction zones since water is in the crust. This shifts the melting curve towards the geotherm for easier melting.
How does water affect subduction?
Water enters the subduction zone in mineral-bound form via hydrous phases (e.g., talc, amphibole, chlorite, and antigorite) within the oceanic lithosphere. As P-T conditions change during subduction, water is released from these minerals and occupies the pore space in the mantle due to dehydration reactions.
Where does melting occur in a subduction zone?
As discussed below, in many subduction zones this melting will occur at depths between fore-arc serpentinites and the source region of arc magmas.
What is the importance of water in magma generation?
Water is a key ingredient in the generation of magmas in subduction zones, and it also influences chemical differentiation that occurs when magmas cool and crystallize in the crust. The source of H2O for arc magma generation is hydrous minerals that are carried into the mantle by the subducting slab.
How does the addition of water causes melting?
How does the addition of water affect the melting temperature of hot rock? When water mixes with hot, dry rock, they cause chemical bonds to break, so that the rock begins to melt. Adding volatiles decreases a rock's melting temperature.
What is the source of the water in a subduction zone quizlet?
What is the source of the water in a subduction zone? Breakdown of water-bearing minerals, such as micas, through metamorphism.
How does subduction trigger melting?
In a subduction zone (like the Cascades or the Andes) where an oceanic plate slides down under another plate that downgoing slab releases its water as it heats up. That water then rises up into the mantle above it causing it to melt at a lower temperature and bam!
How water gets into magma at subduction zones?
The water gradually seeps upward into the overlying wedge of hot mantle. The addition of water to the already hot mantle rocks lowers their melting temperature resulting in partial melting of ultramafic mantle rocks to yield mafic magma.
How does the addition of water cause melting?
How does the addition of water affect the melting temperature of hot rock? When water mixes with hot, dry rock, they cause chemical bonds to break, so that the rock begins to melt. Adding volatiles decreases a rock's melting temperature.
How is melt generated at subduction zones?
The water gradually seeps upward into the overlying wedge of hot mantle. The addition of water to the already hot mantle rocks lowers their melting temperature resulting in partial melting of ultramafic mantle rocks to yield mafic magma. Melting aided by the addition of water or other fluid is called flux melting.
How does water affect the melting point of magma?
Water, they suggest, increases melting but makes the melt less viscous, speeding its transport to the surface, rather like mixing water with honey makes it flow quicker. Because water-laden magma flushes out so quickly, there is less of it in the mantle at any given moment even though more is being produced over time.
What happens at a subduction zone quizlet?
The region where an oceanic plate sinks down into the asthenosphere at a convergent boundary, between continental and oceanic plates. Where two plates are moving apart, magma comes up to create new crust. A geologic feature in the seafloor produced by the descending plate during subduction.
What causes decompression melting?
Decompression melting takes place within Earth when a body of rock is held at approximately the same temperature but the pressure is reduced. This happens because the rock is being moved toward the surface, either at a mantle plume (a.k.a., hot spot), or in the upwelling part of a mantle convection cell.
What is the most important factor producing melting in a subduction zone?
Melting aided by the addition of water or other fluid is called flux melting. It is somewhat more complicated than this, but metamorphic dewatering of suducting crust and flux melting of the mantle wedge appears to account for most of the magma at subduction zones.
Why water is released from the subducted oceanic crust?
Eventually, when the pressure and temperature rise sufficiently, deep within the subduction zone, this serpentine begins to dehydrate, releasing water that makes its way back to the surface through volcanic activity.
How does water affect the melting temperature of rock?
The higher the water content of the rocks, the lower the melting point, meaning that they require less heat to melt. The water mixes with the rock particles and speeds up the formation of crystals.
How does water cause melting?
For a rock, water behaves as its salt. Add water into a mantle peridotite and it will melt at a lower temperature because the bonds in the minerals that make up the rock will be disrupted by the water molecule (we call it a "network modifier").
What happens at a subduction zone?
Subduction zones are plate tectonic boundaries where two plates converge, and one plate is thrust beneath the other. This process results in geohazards, such as earthquakes and volcanoes.
What happens at a subduction zone boundary?
These plates collide, slide past, and move apart from each other. Where they collide and one plate is thrust beneath another (a subduction zone), the most powerful earthquakes, tsunamis, volcanic eruptions, and landslides occur.
Does decompression melting occur at subduction zones?
As hot, low-viscosity asthenosphere upwells into the corner, melting is triggered by decompression. The amount of decompression melting generated at the arc depends somewhat on the subduction rate, with greater subduction rates generating larger amounts of melting.
How does higher water content affect a rocks melting point?
The higher the water content of the rocks, the lower the melting point, meaning that they require less heat to melt. The water mixes with the rock particles and speeds up the formation of crystals.
Why are subduction zones important?
The geologic activity at subduction zones is enormously beneficial to all mankind. Dry land exists only because of subduction. Continents are born from the destruction of oceanic crust. The magma produced at subduction zones hardens into granite, the bedrock of all the continents.
What happens in subduction zones?
These plates collide, slide past, and move apart from each other. Where they collide and one plate is thrust beneath another (a subduction zone), the most powerful earthquakes, tsunamis, volcanic eruptions, and landslides occur.
Where does the water come from in subduction zones?
Water is also cycled through the Earth's crust, at giant subduction zones where oceanic rocks and the overlying ocean sediments are dragged down into the Earth's mantle, sucking water in with it.
How does water affect melting?
The effect of water on rock melting is to increase melting by decreasing the temperature required to melt the rock.
What role does water have in partial melting?
The origin for the stimulating effect of water on melting lies in that water as an incompatible component has a strong tendency to be enriched in the melt (i.e., with a mineral-melt partition coefficient much smaller than unity), thereby lowering the Gibbs free energy of the melt.
How does water content affect melting point?
Water, they suggest, increases melting but makes the melt less viscous, speeding its transport to the surface, rather like mixing water with honey makes it flow quicker. Because water-laden magma flushes out so quickly, there is less of it in the mantle at any given moment even though more is being produced over time.
Does oceanic crust melt in subduction zones?
In most subduction zones, substantial partial melting of subducting oceanic crust will only occur if high shear stresses ( > ∼ 100 MPa) can be maintained by rocks close to, or above, their melting temperatures.
Does water increase the melting point?
In other words, generally when you add a solute to water, the melting point decreases, but only until you add enough solute that the eutectic point is reached, beyond which adding more solute increases the melting point. For example, in the diagram, above, A is the eutectic point.
How does water affect the melting temperature of a mineral?
The higher the water content of the rocks, the lower the melting point, meaning that they require less heat to melt. The water mixes with the rock particles and speeds up the formation of crystals.