A melt forms when solid materials become hot and transform into liquid

molten rock is a type of melt

magma is molten rock beneath the earths surface - underground melt

lava is molten rock that has flowed out onto the earths surface

igneous rocks are made by the freezing or crystallization of a melt

obsidian- sharpest thing on the planet

obsidian is an extrusive igneous rock - no crystals

igneous rocks form through the cooling and solidification of magma or lava

igneous rocks can either form below the surface or on the surface

below the surface creates intrusive plutonic rocks where you can see the crystals

on the surface creates extrusive volcanic rocks where you can’t see the crystals

granite is an intrusive igneous rock

the outer core is made of mostly iron and nickel

earth’s crust and mantle are primarily composed of solid rock

magma is generated in the uppermost mantle

greatest amounts of magma are produced at divergent plate boundaries (seafloor spreading)

lesser amounts of magma is produced at subduction zones (convergent plate boundaries involving the subduction of oceanic crust)

the geothermal gradient is when temperatures in the upper crust increase about 25 degrees C per km

rocks in the lower crust and upper mantle are near BUT NOT AT their melting points

peridotite is an intrusive ultramafic igneous rock found in the mantle

3 Ways to generate magma:

• decompression melting- rapid decrease in pressure can cause the mantle to melt, even without an increase temperature (mid ocean ridges, continental rifts, mantle plumes/hot spots

• addition of volatiles- volatiles are chemical compounds that lower the melting temperature of the rock (subduction zones)

• addition of heat - induces melting if temperature exceeds melting temperature (mantle plumes/hot spots

decompression melting: if the pressure affecting hot mantle rock decreases while the temperature remains unchanged, magma forms

Decompression- melting due to a decrease in pressure

Because pressure prevents melting, a decrease in pressure can permit melting

Three environments where decompression melting occurs: mantle plume/hot spot, continental rift, mid-ocean ridge

Melting crust forms rhyolitic magma

basaltic magma heats the crust

Addition of heat induces melting if temperature exceeds melting temperature

gases/volatiles give magmas their explosive character

Water vapor (h2o) is the most abundant volcanic gas

felsic/rhyolitic magmas are the most explosive

Bowen’s reaction series:

• minerals crystallize in a systematic fashion based on their melting points

• as minerals crystalize, composition of the liquid portion of the magma continually changes

assimilation- magma incorporates some of the surrounding rock

magma mixing- the more buoyant mass may overtake the slower rising body

environment in which magma cools and completely solidifies to form a rock determines- type of rock (composition), appearance of the rock as seen in its texture, and type of rock body

extrusive or volcanic igneous rocks- magma erupts onto surface, lower temps, rapid cooling

intrusive or plutonic igneous rocks- magma is below surface, high temps, slow cooling

explosive extrusive eruptions- high gas content and high viscosity, gas bubbles build pressure, the bubbles burst at low pressure of the surface, when the bubbles burst the magma fragments into pyroclasts and tephra ash

non explosive (effusive) extrusive eruptions- low gas and low viscosity magmas, begin with fire fountains, produces lava flows on surface, produce pillow lavas if erupted beneath water

main types of intrusive environments- dike, still, laccolith, pluton

igneous dike example- grand canyon at Hance rapids