Rock Cycle & Igneous Rocks

Rock Cycle & Igneous Rocks

The Rock Cycle

Differences between rocks and minerals

Minerals Rocks

Pure (made of same substance)

More than one mineral

Some have crystals Not single crystals

No fossils Some have fossils

Usually have shape No definite shape

The Rock Cycle-Types of Rocks

• Rocks are any solid mass of mineral or mineral-like matter occurring naturally as part of our planet.

• Types of Rocks

1. Igneous rock is formed by the crystallization of molten magma.

Rock Cycle-Types of Rocks

2. Sedimentary rock is formed from the weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented.

3. Metamorphic rock is formed by the alteration of pre-existing rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids.

The Rock Cycle

• Rock Cycle: shows the interrelationships among the three rock types (igneous, sedimentary, and metamorphic)

• Magma is molten material that forms deep beneath the Earth’s surface.

• Lava is magma that reaches the surface.

• Weathering is a process in which rocks are broken down by water, air, and living things.

• Sediment is weathered pieces of Earth elements.

The Rock Cycle

Energy that drives the Rock Cycle

Earth’s Interior (Internal Processes): Igneous & Metamorphic Rocks

Sun (External processes): Sedimentary rocks.

Weathering and the movement of weathered materials are external processes powered by energy from the sun.

Igneous Rocks & Magma

Igneous Rocks

Named for the Latin ‘Ignis’=FireOccurrence

Found globally Found in discrete geologic locations

Convergent plate boundaries Divergent plate boundaries Mantle plumes

Formed by the crystallization of magma or lava

The Nature of Igneous RocksForm from Magma [Greek=“paste”]

Hot, partially molten mixture of solid, liquid, and gas

Gases: H2O, CO2, etc. less dense than solid rocksolidifies upon cooling

Magma Vs. Lava (again)

Magma vs. LavaMagma: molten rock beneath the

surfaceLava: molten rock that has reached

the surfaceMagma: form intrusive igneous

rocksLava: form extrusive igneous rocks

Igneous Rocks in NM- Cornudas Peak

Magma Composition

Composition varies widelyOxygen plus major elementsGenerally a silica (SiO2) meltSilica and water content control

viscositySilica content used in classification

Mafic Magmas

Silica content ~ 50%High Fe, Mg and Ca (Iron,

Magnesium, and Calcium) High temperature molten magma

1000o to 1200oC (1800-2200oF)Major minerals:

Olivine - Ca PlagioclasePyroxene

Rocks formed from Mafic Magmas

Felsic Magma

Silica content: 65-77%High Al, Na and K (Aluminum, Sodium, Potassium)

Lower temperature magmasLess than 850oC (1575 oF)

Major minerals:Feldspars - MicasQuartz

Magma Viscosity

Viscosity: resistance to flow

High Viscosity= HIGH resistance, SLOWER flow

Low Viscosity=LOW resistance=FASTER flow

Magma Viscosity

• Controlled by silica and water content, and temperature

• As magma cools-silica tetrahedron form links

• Linkages control viscosity

Magma Viscosity

High Silica=high viscosity (slow)Low Silica=low viscosity (fast)

Cooler Temperatures=higher viscosityHigher Temperatures=lower viscosity

More Links=higher viscosityFewer Links=lower viscosity

Water=lower viscosity

Plate Tectonic Setting of Igneous Rocks

Divergent Plate Boundaries Partial melting of mantle produces basaltic

magma (MAFIC)Convergent Plate Boundaries

Subduction produces partial melting of basalt, sediments, parts of mantle

Andesitic and rhyolitic magma (INTERMEDIATE & FELSIC)

Ascending magma assimilates lower crustal material

Plate Tectonic Setting of Igneous Rocks

Mantle Plumes Partial melting of plumes of mantle material Basaltic magma is produced (MAFIC) Rising magma produce

Intraplate island chains Flood basalt [Columbia River Basalts]

Igneous Rocks-Classification

Igneous Rocks are classified by 3 main factors:1. Formation (by magma or lava)2. Texture3. Composition

Igneous Rocks: Classification

Formation Intrusive Igneous Rocks:

formed when magma hardens beneath Earth’s surface.

See these after erosion occurs Ex: Granite

Extrusive Igneous Rocks: Formed when lava hardens above Earth’s surface Ex: Rhyolite

Granite

Rhyolite

Igneous Rocks: Classification

Texturethe size, shape and relationship of

minerals in the rockCooling history of the magma or lavaCrystal size increases as rate of cooling

slowsThere are 5 main textures: coarse, fine,

glassy, porphyritic, pyroclastic

Igneous Rocks: Classification

Coarse (Phaneritic)TextureSlow cooling rateLarge CrystalsEquigranular, interlocking crystalsEx. Granite

Igneous Rocks: Classification

Fine (Aphanitic)TextureFast cooling rateSmaller, interconnected crystalsFew crystals visible in hand specimenEx. Rhyolite

Igneous Rocks: Classification

Glassy TextureVery fast cooling rateNo visible crystalsVolcanic GlassEx. Obsidian

Igneous Rocks: Classification

Porphyritic TextureComplex cooling historyDifferent cooling rates throughout the

rockDifferent sized crystalsEx. Andesite

Igneous Rocks: Classification

Pyroclastic Textureforms as an explosive volcanic eruption

mixes fragments of the volcano with hot ash in the atmosphere

As this hot combination of tiny ash particles and larger, angular fragments settles to the ground, they blanket the Earth's surface and weld together

Appear porphyritic with visible crystalsA generic term for all these rocks is “tuff”

Igneous Rocks: Classification

Composition Which types of minerals make up the rock Composition determined by Bowen’s reaction

series (later) Range from light colored (felsic) to very dark

colored (ultramafic)

Igneous Rocks: Classification

Felsic Composition Also called silicic or granitic

composition Light colored rocks White to pink in color Mostly composed of quartz and

potassium feldspar Very High amounts of: Si, Na, K Very Low amounts of: Fe, Mg, Ca Examples: Granite (I) Rhyolite (E)

Felsic Rocks

Igneous Rocks: Classification

Intermediate Composition Also called andesitic composition Combination of light and dark colored

minerals Salt and Pepper OR gray coloration Mostly composed of amphibole,

plagioclase feldspar, quartz, pyroxene High amounts of: Si, Na, K Low amounts of: Fe, Mg, Ca Examples: Diorite (I) Andesite (E)

Intermediate Rocks

Igneous Rocks: Classification

Mafic CompositionAlso called basaltic compositionDark colored mineralsMostly composed of pyroxene,

plagioclase feldspar, olivineLow amounts of: Si, Na, KHigh amounts of: Fe, Mg, CaExamples: Gabbro (I) Basalt (E)

Mafic Rocks

Igneous Rocks: Classification

Ultramafic CompositionVery Dark colored minerals (usually

has dark greens)Mostly composed of pyroxene and

olivineVery Low amounts of: Si, Na, KVery High amounts of: Fe, Mg, CaExamples: Peridotite (I) Komatiite (E)

Ultramafic Rocks

Classification of Igneous Rocks

Classification of Igneous Rocks

Bowen’s Reaction Series

Chemical Evolution of Igneous Rocks proposed by Norman Bowen in the early 1900s.

Proposed mafic magmas may evolve by cooling and crystallization to produce more silica-rich magmas

Found the following through experiment:1. There is a regular sequence of silicate mineral

crystallization Minerals common to mafic rocks crystallize at the

highest temperatures Minerals common to felsic rocks crystallize at the

lowest temperatures

Bowen’s Reaction Series

Once a mineral forms, it will undergo a chemical reaction with the surrounding melt to produce the next  lower temperature mineral in the sequence

Example: Olivine undergoes a reaction with the surrounding melt to form pyroxene. Pyroxene reacts with the surrounding melt to form amphibole, etc.

Bowen’s Reaction Series

There are two important parts of the reaction series: a) The discontinuous series - includes minerals

with differing arrangement of Si-O tetrahedra; (olivine, pyroxene, amphibole, biotite)

b) The continuous series - includes plagioclase feldspar minerals, all of which are framework silicates; (Ca-rich plagioclase (anorthite), Na-rich plagioclase (albite))

Bowen’s Reaction Series

Importance of Bowen’s Reaction Series

Explains how a variety of igneous rock types can come from a single (mafic) magma composition Fractional Crystallization Crystal Settling Volcanic Eruption

Allows interpretation of crystallization temperature based on mineralogical composition. Ultramafic=highest temps Felsic=lowest temps