esc102- igneous rocks

igneous

form by cooling/crystallization of magma

intrusive (plutonic)

magma emplaced in subsurface (magmatic chamber)

extrusive (volcanic)

lava extruded at surface

Magma

molten rock in subsurface

lava

Magma that reaches Earth's surface

how to differentiate in/extrusive

in- can see different minerals and cools slow

ex- cant see minerals, cools rapidly

Aphanitic

crystals too small to see with naked eye

how magma originates

temp, pressure, volatiles, composition

temp of magma

geothermal gradient (20-30 deg/1km)

at 100km: 1200-1400 deg. (melting temp of upper mantle)

pressure of magma

higher pressure, higher melting temp.

decompression melting- rock near melting temp close to surface

volatiles of magma

water in magma. more water, lower melting temp

composition of magma

mafic, high temp, dark mg, fe. felsic, low temp, light, si.

decompression melting

caused by upwell at spreading plates

flux-induced melting

water released by subducted slab induces melting above

Three Parts of Magma

melt- liquid

solids- silicates/minerals

volatiles- H20, CO2, SO2

crystallization of magma

liquids and solids seperate to chemically distinct units

evolution of magma

-fraction crystallization

-assimilation of host rock

-magma mixing

igneous rock classification

texture- size/shape of crystals

composition- chemical/mineral composition

phaneritic

visible grans. plutonic have this

aphanitic

fine grained. extrusive

equigranular

equal sized crystals

porphyritic

large, well-formed crystals surrounded by finer-grained crystals

vesicular

holes from escaping gas

gas bubbles trapped in cooling lava forms holes

obsidian

natural glass from felsic lava.

forms when viscous lava cools fast

pumice

froth natural glass

forms from rapid cooling of frothy lava

Phenocrysts

large crystals in porphyritic rocks

forms when magma solidifies slowly then erupts and rest solidifies quickly

pyroclastic

form when fragments of rocky mineral ejected by eruptions

tephra

air borne pyroclastic. initially unconsolidated