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Rock Cycle & Igneous Rocks
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Rock Cycle & Igneous Rocks

Feb 22, 2016

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Rock Cycle & Igneous Rocks. The Rock Cycle. Differences between rocks and minerals. 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. - PowerPoint PPT Presentation
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Page 1: Rock Cycle & Igneous Rocks

Rock Cycle & Igneous Rocks

Page 2: Rock Cycle & Igneous Rocks

The Rock Cycle

Page 3: Rock Cycle & Igneous Rocks

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

Page 4: Rock Cycle & Igneous Rocks

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.

Page 5: Rock Cycle & Igneous Rocks

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.

Page 6: Rock Cycle & Igneous Rocks

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.

Page 7: Rock Cycle & Igneous Rocks

The Rock Cycle

Page 8: Rock Cycle & Igneous Rocks

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.

Page 9: Rock Cycle & Igneous Rocks

Igneous Rocks & Magma

Page 10: Rock Cycle & Igneous Rocks

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

Page 11: Rock Cycle & Igneous Rocks

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

Page 12: Rock Cycle & Igneous Rocks

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

Page 13: Rock Cycle & Igneous Rocks

Igneous Rocks in NM- Cornudas Peak

Page 14: Rock Cycle & Igneous Rocks

Magma Composition

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

viscositySilica content used in classification

Page 15: Rock Cycle & Igneous Rocks

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

Page 16: Rock Cycle & Igneous Rocks

Rocks formed from Mafic Magmas

Page 17: Rock Cycle & Igneous Rocks

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

Page 18: Rock Cycle & Igneous Rocks
Page 19: Rock Cycle & Igneous Rocks

Magma Viscosity

Viscosity: resistance to flow

High Viscosity= HIGH resistance, SLOWER flow

Low Viscosity=LOW resistance=FASTER flow

Page 20: Rock Cycle & Igneous Rocks

Magma Viscosity

• Controlled by silica and water content, and temperature

• As magma cools-silica tetrahedron form links

• Linkages control viscosity

Page 21: Rock Cycle & Igneous Rocks

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

Page 22: Rock Cycle & Igneous Rocks

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

Page 23: Rock Cycle & Igneous Rocks

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]

Page 24: Rock Cycle & Igneous Rocks
Page 25: Rock Cycle & Igneous Rocks

Igneous Rocks-Classification

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

Page 26: Rock Cycle & Igneous Rocks

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

Page 27: Rock Cycle & Igneous Rocks

Granite

Page 28: Rock Cycle & Igneous Rocks

Rhyolite

Page 29: Rock Cycle & Igneous Rocks

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

Page 30: Rock Cycle & Igneous Rocks

Igneous Rocks: Classification

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

Page 31: Rock Cycle & Igneous Rocks

Igneous Rocks: Classification

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

Page 32: Rock Cycle & Igneous Rocks

Igneous Rocks: Classification

Glassy TextureVery fast cooling rateNo visible crystalsVolcanic GlassEx. Obsidian

Page 33: Rock Cycle & Igneous Rocks

Igneous Rocks: Classification

Porphyritic TextureComplex cooling historyDifferent cooling rates throughout the

rockDifferent sized crystalsEx. Andesite

Page 34: Rock Cycle & Igneous Rocks

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”

Page 35: Rock Cycle & Igneous Rocks
Page 36: Rock Cycle & Igneous Rocks

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)

Page 37: Rock Cycle & Igneous Rocks

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)

Page 38: Rock Cycle & Igneous Rocks

Felsic Rocks

Page 39: Rock Cycle & Igneous 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)

Page 40: Rock Cycle & Igneous Rocks

Intermediate Rocks

Page 41: Rock Cycle & Igneous 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)

Page 42: Rock Cycle & Igneous Rocks

Mafic Rocks

Page 43: Rock Cycle & Igneous 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)

Page 44: Rock Cycle & Igneous Rocks

Ultramafic Rocks

Page 45: Rock Cycle & Igneous Rocks

Classification of Igneous Rocks

Page 46: Rock Cycle & Igneous Rocks

Classification of Igneous Rocks

Page 47: Rock Cycle & Igneous Rocks
Page 48: Rock Cycle & 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

Page 49: Rock Cycle & Igneous Rocks

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.

Page 50: Rock Cycle & Igneous Rocks

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))

Page 51: Rock Cycle & Igneous Rocks

Bowen’s Reaction Series

Page 52: Rock Cycle & Igneous Rocks

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