Rock Cycle & Igneous Rocks

The Rock Cycle

Differences between rocks and minerals 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’=Fire Occurrence 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 Rocks Form from Magma [Greek=“paste”] Hot, partially molten mixture of solid, liquid, and gas Gases: H2O, CO2, etc. less dense than solid rock solidifies upon cooling

Magma vs. Lava Magma Vs. Lava (again) Magma: molten rock beneath the surface Lava: molten rock that has reached the surface Magma: form intrusive igneous rocks Lava: form extrusive igneous rocks

Igneous Rocks in NM- Cornudas Peak

Composition varies widely Magma Composition Composition varies widely Oxygen plus major elements Generally a silica (SiO2) melt Silica and water content control viscosity Silica 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 Plagioclase Pyroxene

Rocks formed from Mafic Magmas

Felsic Magma Silica content: 65-77% High Al, Na and K (Aluminum, Sodium, Potassium) Lower temperature magmas Less than 850oC (1575 oF) Major minerals: Feldspars - Micas Quartz

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 viscosity Higher Temperatures=lower viscosity More Links=higher viscosity Fewer 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: Formation (by magma or lava) Texture 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 Texture the size, shape and relationship of minerals in the rock Cooling history of the magma or lava Crystal size increases as rate of cooling slows There are 5 main textures: coarse, fine, glassy, porphyritic, pyroclastic

Igneous Rocks: Classification Coarse (Phaneritic)Texture Slow cooling rate Large Crystals Equigranular, interlocking crystals Ex. Granite

Igneous Rocks: Classification Fine (Aphanitic)Texture Fast cooling rate Smaller, interconnected crystals Few crystals visible in hand specimen Ex. Rhyolite

Igneous Rocks: Classification Glassy Texture Very fast cooling rate No visible crystals Volcanic Glass Ex. Obsidian

Igneous Rocks: Classification Porphyritic Texture Complex cooling history Different cooling rates throughout the rock Different sized crystals Ex. Andesite

Igneous Rocks: Classification Pyroclastic Texture forms 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 crystals A 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 Composition Also called basaltic composition Dark colored minerals Mostly composed of pyroxene, plagioclase feldspar, olivine Low amounts of: Si, Na, K High amounts of: Fe, Mg, Ca Examples: Gabbro (I) Basalt (E)

Mafic Rocks

Igneous Rocks: Classification Ultramafic Composition Very Dark colored minerals (usually has dark greens) Mostly composed of pyroxene and olivine Very Low amounts of: Si, Na, K Very High amounts of: Fe, Mg, Ca Examples: 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: 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: The discontinuous series - includes minerals with differing arrangement of Si-O tetrahedra; (olivine, pyroxene, amphibole, biotite) 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