How is the process of freezing magma similar to that of freezing water? How is it different?
erupts out of a volcano and freezes in contact with air or the ocean magma, like water, freezes in colder temperatures than its liquid state
Magma formation: Geothermal Gradient
crustal temperature increases 25 degrees Celsius/km with depth at the base of the lithosphere Temp is ~1,280 degrees Celsius varies from place to place
Why are there so many different types of magmas?
It can be formed and transferred three different ways Magmas vary chemically due to initial source rock composition partial melting assimilation fractional crystallization
Why do magmas rise from depth to the surface of the Earth?
because magma is less dense than rock, it moves upward
What factors control the viscosity of a melt?
temperatures, volatile, and silica
What factors control the cooling time of a magma within the crust?
temperature, viscosity
How does grain size reflect the cooling time of a magma?
reflects the stages of melt it went through and how fast
What does the mixture of grain sizes in a porphyritic igneous rock indicate about its cooling history?
• Initial slow cooling creates large phenocrysts. • Subsequent eruption cools remaining magma quickly
Why does melting take place beneath the axis of a mid-ocean ridge?
Igneous rocks form along mid-ocean ridges because of decompression melting of the rising asthenosphere.
Magma Formation: Pressure Release
rock does not melt in high pressure drop in pressure initiates "decompressional melting"
Magma Formation: Heat Transfer
rising magma carries mantle heat, raising temperature in crustal rock crustal rock melts
Describe the way magmas are produced in subduction zones.
planetesimal and meteorite accretion under the surface of the earth gravitational compression radioactive decay