lec 3: igneous rocks & volcanism

elements: major, minor, trace

major: more than 1%

minor: 0.1 - 1%

trace: less than 0.1%

lithophile

lithophile: elements that bond with oxygen and float → MANTLE & CRUST

• “rock-loving”

partitioning

partitioning of elements btwn minerals in the mantle & magma → ascends to form the crust (essential for understanding igneous rocks)

siderophile

siderophile: elements that disolved into molten (heavy) iron → gravity pulled to CORE

• “iron loving”

chalcophile

chalcophile: elements that most easily form sulfides

atmophile

elements commonly found as gases

incompatible/compatible elements

incompatible: bulky, buoyant (magma)

compatible: fits easily into mantle crystals

methods for melting rock

1. by adding heat

2. by lowering pressure

3. by lowering melting temperature (e.g. adding water)

porphyry

two stages of crystallization:

• early slow growth of large crystals called phenocrysts

• later rapid growth of numerous small crystals called the groundmass

fractional crystallization

minerals perciptate in a particular order

• function of temperature and chemical composition of magma

magma mixing

liquid + liquid magmas blend together

assimilation

liquid + solid: hot magma melts & digests surrounding wall rock

dyke

sheet-like body of rock that cuts discordantly across pre-existing rock layers

effusive eruption

volcanoes erupt explosively with no fragmentation

types of lava: basaltic, flood basalts

basaltic lava: low silica, runny, hot

flood basalts: massive mantle plume (hotspot) cracks oepn and pumps out runny basaltic lava

lahars

dangerous volcanic events