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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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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