Week 3 - Igneous Rocks and Processes

Magma

Liquid molten rock in earth

Forms earth’s mantle and crust (lithospheric mantle_

Geothermal gradient

Heat moves upward by conduction and convection

at great depth temperature alone would melt substances, but high-pressure cause solid to remain

Island arc

product of subduction — mafic, intermediate, or felsic magma depending on degree of fractional crystallization

Continental arc

product of subduction — intermediate to felsic magma

Hot spots

mostly related to plumes — mafic magma in oceanic hot spots/ mafic or felsic magma in continental hot spots

Rift systems

stretching and thinning of the lithosphere

Felsic magma

contains high proportion of elements of silica (lighter colored rocks)

Mafic magma

contains small amount of silica (darker colored rocks)

Intermediate magma

has composition between felsic and mafic

ultramafic

contains less silica than mafic magma

how does magma rise?

magma rises because its less dense than the surrounding rocks; buoyancy drives the magma upward

temperature, composition, viscosity are all elements

Magma flow control (fast or slow — how??)

More explosive = magma with high silica (stickier)

Less explosive = magma with low silica (fluid)

Effusive eruptions

produce lava flows, commonly baslatic lava and for sheild volcanoes

more fluid, less silica

Explosive eruptions

cause by gas pressure being trapped in more viscous magma

magma with low viscosity (more silica0

magma with high silica

densier, low melting points, bigger explosive eruptions, thicker magma

magma with low silica

thin and “runny”, effusive eruptions, high melting points