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Home , Amphibole, Andesite, Augite, Gabbro, Intermediate composition, Olivine

Module 7 Igneous Rocks IGNEOUS ROCKS

▪ Igneous Rocks form by crystallization of molten material IGNEOUS ROCKS

▪ Igneous Rocks form by crystallization of molten rock material

▪ Molten rock material below ’s surface is called ▪ Molten rock material erupted above Earth’s surface is called ▪ The name changes because the composition of the molten material changes as it is erupted due to escape of volatile gases Rocks Cycle

Consolidation

Crystallization Rock FormingRock Intermediate 1200ºC 700ºC High Low

Temperature decreases BOWEN’S REACTION SERIES SiO2 of liquid increases Discontinuous branch

Muscovite

Continuous branch

K- feldspar Na-rich Na-Ca-rich Ca-Na-rich Ca-rich Rock Forming Minerals

Olivine

Ca-rich Pyroxene

Ca-Na-rich Amphibole Na-Ca-rich Continuous branch Continuous

Discontinuous branch Discontinuous Biotite Na-rich Plagioclase feldspar K-feldspar Muscovite Quartz

BOWEN’S REACTION SERIES Rock Forming Minerals High Temperature Suite

Olivine • Isolated Tetrahedra Structure • , , , • Bowen’s Discontinuous Series • Single Chain Structure (Pyroxene) • Iron, magnesium, , silicon, aluminium, oxygen • Bowen’s Discontinuos Series Calcium Feldspar • Framework Silicate Structure (Plagioclase) • Calcium, silicon, aluminium, oxygen • Bowen’s Continuous Series Rock Forming Minerals Intermediate Temperature Mineral Suite • Double Chain Structure (Amphibole) • Iron, magnesium, calcium, silicon, aluminium, oxygen • Bowen’s Discontinuos Series Biotite • Sheet Silicate Structure () • Iron, magnesium, , silicon, aluminium, oxygen • Bowen’s Discontinuos Series Feldspar • Framework Silicate Structure (Plagioclase) • Sodium, silicon, aluminium, oxygen • Bowen’s Continuous Series Rock Forming Minerals Low Temperature Mineral Suite Muscovite • Sheet Silicate Structure (Mica) • Calcium, potassium, silicon, aluminium, oxygen • Bowen’s Discontinuos Series Potassium Feldspar • Framework Silicate Structure () • Potassium, silicon, aluminium, oxygen • Bowen’s Continuous Series Quartz • Framework Silicate Structure • Silicon, oxygen • Last to crystallize from magma Rock Forming Minerals Bowen’s Reaction Series

Olivine

Ca-rich Pyroxene

Ca-Na-rich Amphibole Na-Ca-rich Continuous branch Continuous

Discontinuous branch Discontinuous Biotite Na-rich Plagioclase feldspar K-feldspar Muscovite Quartz

BOWEN’S REACTION SERIES Rock Forming Minerals Bowen’s Reaction Series

Plagioclase

Olivin Rock Forming Minerals Bowen’s Reaction Series

Felspar zoning Effect of Cooling Rate on Size

▪ are formed by arranged in orderly patterns ▪ Crystal size is determined by the rate of cooling ➢Extremely fast cooling ➢Fast cooling ➢Slow cooling Effect of Cooling Rate on Crystal Size

Extremely fast cooling

❑ Forms glass, not crystals ❑ Occurs above Earth’s surface under water or ice ❑ Yields , volcanic glass Effect of Cooling Rate on Crystal Size

Fast cooling

❑ Forms very small invisible crystals ❑ Crystallized out less slowly ❑ Magma moved more rapidly ❑ Occurs closer to Earth’s surface ❑ Typical in small intrusions and conduit Effect of Cooling Rate on Crystal Size

Slow cooling

❑ Forms large, visible crystals ❑ The slower the cooling rate, the larger the crystals formed ❑ Occurs below Earth’s surface ❑ Typical of plutonic rocks Where do the igneous rocks form? Volcanic (Extrusive) Rocks

Plutonic (intrusive) Rocks Where do the igneous rocks form? Plutonic (intrusive) Igneous Rocks

Plutonic (intrusive) Rocks Form by crystallization of molten rock material below Earth’s surface

Coarse-grained plutonic Fine-grained plutonic rocks rocks Crystallized out very slowly in Crystallized out less slowly, large magma chambers 12-20 km more rapidly, in small beneath Earth’s surface intrusions and conduits closer to Earth’s surface Where do the igneous rocks form? Plutonic (intrusive) Igneous Rocks Where do the igneous rocks form? Plutonic (intrusive) Igneous Rocks

Laccolith • are masses of between layers of the surrounding rock Where do the igneous rocks form? & Where do the igneous rocks form? Plutonic (intrusive) Igneous Rocks

Dike & Sill • are tabular intrusive bodies. • Dikes cut across layer of the surrounding rock • Sills are injected between layers of strata Where do the igneous rocks form? Volcanic (extrusive) Igneous Rocks Volcanic (Extrusive) Igneous Rocks Form by crystallization of molten rock material above Earth’s surface

Lavas Pyroclastic volcanic rocks are flowing out (extruded) are blasted out

Ash Blocks Bombs is very fine- are large are large grained blocks that molten blocks pyroclastic are blasted that are material out blasted out Where do the igneous rocks form? Volcanic (extrusive) Igneous Rocks A lava fountain and rapidly flowing

Pahoehoe, a smooth-surfaced, ropy form of basalt that crystallizes out near the AA, a jagged-surfaced form of beginning of a basalt flow basalt that crystallizes out at the end of a basalt flow Basalt, a composition lava Where do the igneous rocks form? Volcanic (extrusive) Igneous Rocks

Andesite flow, flow, Mexico Cascade Range, Oregon

Andesite, an lava Where do the igneous rocks form? Volcanic (extrusive) Igneous Rocks

Rhyolite dome, Mono Craters, California

Rhyolite flow showing columnar jointing, MacDougalls Island, New Brunswick

Rhyolite, a composition lava Where do the igneous rocks form? Volcanic (extrusive) Igneous Rocks

Pyroclastic Eruption, Eruption of Mount St. Helens, Washington, 1980 Where do the igneous rocks form? Volcanic (extrusive) Igneous Rocks

Other Notable Pyroclastic Volcanic Eruptions Igneous Rocks Texture (4 textures) Igneous Rocks Texture

A phaneritic texture • Consists of visible grains • Is formed by very slow cooling below Earth’s surface • Characteristic of plutonic igneous rocks i.e. , , , Igneous Rocks Texture

Aphanitic texture • Consists of invisible grains formed by fast rate of cooling • Characteristic of the : basalt, andesite, rhyolite Igneous Rocks Texture

Glassy texture • Consists of visible grains • Is not crystalline, is formed by extremely rapid cooling • Characteristic of Obsidian Igneous Rocks Texture

Vesicular texture • Is bubbly, formed by trapped bubbles of gas • Characteristic of (vesicular basalt) and (vesicular rhyolite) Igneous Rocks Texture

Porphyritic texture • Consists of phaneritic (visible) grains in an aphanitic •Phaneritic crystals form by very slow cooling below Earth’s surface •Aphanitic crystals form by very rapid cooling above Earth’s surface • Characteristic of the lavas: basalt, andesite, rhyolite • Formed when a lava is erupted as a Texture and where they form ABOVE EARTH’S SURFACE Based on Where They Form and Their Texture

Glassy Texture Plutonic (intrusive) Igneous Rocks Volcanic (Extrusive) Igneous Rocks CLOSER EARTH’S SURFACE

Aphanitic Texture Texture

Phaneritic Texture BELOW EARTH’S SURFACE Igneous Rocks Composition

Ultramafic • Means rich in magnesium and iron • Is the average composition Dunit (Olivine rich) of Earth’s • Composed of olivine and augite • Example:

Harzburgit (Pyroxene rich) Igneous Rocks Composition

Mafic • Means rich in magnesium, iron, and/or calcium • Is the average composition of oceanic • Composed of olivine, augite, and calcium, plagioclase feldspar • Examples: basalt, diabase, and gabbro Igneous Rocks Composition

Intermediate • Means half mafic, half felsic • Is the composition of a mixture of oceanic and ? • Composed of hornblende and calcium-sodium plagioclase feldspar • Examples: andesite and diorite Igneous Rocks Composition

Felsic • Means rich in feldspar and silica • Is the average composition of continental crust • Composed of potassium feldspar, sodium plagioclase feldspar, quartz • Examples: rhyolite and granite Classification and naming of igneous rocks Identification of Plutonic Igneous Rocks Plutonic Rocks

Phaneritic texture

Mafic composition Intermediate composition Felsic composition Dark gray Medium gray, Light gray ~ 50:50 black and white or pink Diabase (fine-grained) Diorite Granite Gabbro (coarse-grained) ClassificationIdentification and ofnaming Volcanic of Igneous igneous Rocks rocks Identification of Volcanic Igneous Rocks Volcanic Rocks

Vesicular texture Glassy texture Scoria Obsidian Mafic composition Aphanitic Dark gray matrix The lavas Pumice Felsic composition Light gray

Basalt Andesite Rhyolite Mafic composition Intermediate composition Felsic composition Dark gray Medium gray or Light gray greenish gray or pink Usually porphyritic Temperature decreases ORIGIN EVOLUTIONAND OF IGNEOUS ROCKS

SiO2 of liquid increases BOWEN’S REACTION SERIES Discontinuous branch Olivine Pyroxene Amphibole Biotite

Muscovite Quartz

Continuous branch

K-feldspar Plagioclase feldspar Na-rich Na-Ca-rich Ca-Na-rich Ca-rich PERIDOTITE Phaneritic Plutonic

GRANITE DIORITE GABBRO TEXTURE ORIGIN Volcanic Aphanitic

RHYOLITE ANDESITE BASALT Classification and naming of igneous rocks

Obsidian (volcanic glass) Scoria (vesicular basalt) Pumice (vesicular rhyolite) Basalt Porphyritic Andesite Rhyolite Gabbro Diorite Granite Hamblin 2009 Hamblin 2009