Lecture: Igeneous rocks

Rocks formed by the cooling and solidification of magma or lava

Molten rock Originates from partial melting of solid rock because it is less dense than surrounding rock, it rises toward the surface

When magma erupts out of a volcano, it is called lava

Three major components of magma Melt (liquid component) Crystals (solid component) Volatiles (gasesous component)

Contains mobile ions of common crustal elements Silicon, Oxygen Aluminum

Some magma contains suspended silicate mineral crystals As cooling progresses, more crystals form, making magma more viscous

Gases that escape as the pressure decreases Ex. Water vapor, carbon dioxide, sulfur dioxide Volatiles propel eruptions and influence magma behavior

Form at the surface from lava flows or volcanic debris Common in volcanic areas Ex. Basalt, Rhyolite, Andesite

Crystallize below Earth’s surface Found in locations where uplift and erosion have exposed deep-seated rocks Ex. Granite, Diorite, Gabbro

Primarily composed of silicate minerals

Rich in silica, potassium, sodium, and calcium Ex. Quartz, Mica, Feldspar

Rich in iron and magnesium Ex.Olivine

Felsic, Intermediate Mafic Ultramafic

Dominated by light-colored silicates Contains 70% silica, making it viscous magma and lower in temperature Found in continental crust

25 - 45% dark silicate minerals mized with plagioclase feldspar Associated with volcanic island arcs

At least 45% dark silicates Denser and darker than felsic rocks commonly forming oceanic crust Fluid magma Basalt is the most common mafic rock

Mostly ferromagnesian minerals Low silica content, very high in magnesium and iron Main component of Earth’s mantle

Aphanitic Phaneritic Porphyritic Vesicular Glassy Pyroclastic

Decompression melting Flux melting Heat transfer melting

Lowering pressure reduces the melting temperature of rocks Rocks deep in the mantle remain solid due to high pressure When pressure decreases rocks begin to melt Produces basaltic magma, common at mid-ocean ridges and hot spots

Water lowers the melting temperature of hot mantle rocks by creating impurities in the crystal structure Occurs at subduction zones where oceanic crust descends Generates volatile-rich magma leading to explosive volcanism

Rising mantle-derived magma heats surrounding crustal rocks

Basaltic magma rises and ponds beneath continental crust Heat melts felsic crustal rocks, forming silica rich magma

Rocks melt over a range of temperatures and partial melting produces magma that is different in composition from the original rock