Igneous Petrology (intro) Flashcards by Deann Tatco

Known as “primary rocks” that originated from solidified magma or lava.

Igneous rock

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Known as “secondary rocks” which formed as a result of lithified fragments of pre-existing rocks.

Sedimentary

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Rocks that formed as a result of pre-existing rocks undergoing metamorphism due to being subjected to heat, pressure, and fluids.

Metamorphic

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rock that consists of multiple crystals of a single mineral.

Monomineralic rock

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A rock that consists of multiple types of minerals and/or mineraloids.

Polymineralic rock

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A model showing the origins, relationships and processes between rock types and other geologic materials.

Rock cycle

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A model showing the origins, relationships and processes between rock types and other geologic materials.

Rock cycle

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Magma is generated by

Partial melting

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contains liquids, crystals, gases, and rock fragments in varying proportions depending upon temperature, pressure and chemistry conditions.

Magma

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Magma that rises and erupts onto the surface of Earth.

Lava

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The liquid portion of the magma.

Melt

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The gaseous portion of the magma (H20, COz, S, Cl, F).

Volatiles

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The solid portion of the magma.

Crystal

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The processes were the magma or lava looses its heat and crystallizes.

Crystallization

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Rocks that formed as a result of crystallization of magma or lava

Igneous rocks

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Igneous rocks that formed beneath the surface as a result of loosing mobility.

Plutonic rock

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Other name for intrusive igneous rock

Plutonic rock

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Will tend to have larger crystal sizes as they have time to grow.

Plutonic rocks

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Igneous rocks that solidified at the surface as a result of extrusion.

Extrusive rock

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Will tend to have smaller crystal sizes as they rapidly cool and crystallize from the cooler environment.

Volcanic rock

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The process where your pre-existing rock is heated to the point of partially melting.

Partial melting

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The partial melting within the Earth’s crust.

Anatexis

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When magmas that were generated by some other mechanism intrude into cold crust, they bring with them heat. Upon solidification, they lose this heat and transfer it to the surrounding crust

Temperature increase

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Increase of temperature with depth

Geothermal gradient

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Known as adiabatic melting

Decompression melting

occurs as a result of decrease in pressure in the system.

Decompression melting

Where do decompression melting occur

Divergent plate boundaries

Agents that reduces melting temperature of a substance.

Flux

The presence of volatiles in rocks acts as fluxes, weakening the bonds of atoms in the minerals, such as the Si-o bond, making them easier to melt.

Addition of volatile

Where do addition of volatiles usually occur

Subduction zone

Occurs when crystallization along the walls of the magma chamber in which crystals preferentially form and adhere to the edges.

Marginal accretion

Includes fractionation processes that occur when crystals develop with significantly different densities than the surrounding magma.

Gravitational separation

A process during fractional crystallization where the first dense minerals that mineralize SINK and accumulate at the BOTTOM of the magma body.

Crystal settling

process during fractional crystallization where the first lighter minerals that mineralize FLOAT and accumulate at the top of the magma body.

Crystal floatation

process during magma cooling that occurs when the magma body is subjected to stress, squeezing off the melt from the magma body,

Filter pressing

Occurs whereby liquids and crystals are segregated due to factors such as velocity, density or temperature.

Convective flow segregation

Two or more dissimilar magmas coexist but retaining their distinctive characteristics.

Magma mingling

Thorough mixing of two or more magmas, with the individual characteristics no longer recognizable.

Magma mixing

Thorough mixing of two or more magmas, with the individual characteristics no longer recognizable.

Magma Mixing

The incorporation and digestion of solid or fluid foreign materials, such as the wall rock.

Magmatic assimilation

Inclusions in magmatic bodies.

Xenolith

One parent magma fractionates to produce two or more distinctly different daughter magmas with different compositions.

Liquid fractionation

Involves the selective diffusion of ions in the magma due to compositional, thermal or density gradients, and water content,

Differential diffusion

Also known as liquid-liquid fractionation,

Liquid immiscibility

separation of magma into two or more distinct immiscible liquid phases.

Liquid immiscibility

A graphical method used to discriminate samples through their chemical content into correctly identifying an igneous rock.

Variation diagram

Igneous rocks that are dominantly composed of dark-colored silicates, but can commonly appear green,

Ultramafic

These are major constituents of ophiolites and mantle.

Ultramafic

Igneous rocks that are dominantly composed of dark-colored silicates, such as pyroxenes, plagioclase and amphiboles.

Mafic

These are major constituents of oceanic crusts.

Mafic

Also called as basaltic

Mafic

Igneous rocks that are gray-colored to salt-and-pepper, depending on the size of the mineral grains.

Intermediate

These are major constituents of volcanic arcs.

Intermediate

Igneous rocks that are dominantly composed of light-colored silicates, such as quartz and feldspars.

Felsic

These are major constituents of continental crust.

Felsic

A direct type of classification of composition that involves visual comparison of minerals and determining their volume percentages.

Modal classification

indirect type of classification of composition that analyzes the chemical composition of rocks.

Normative classification

SiO2% content of ultrabasic

Less than 45

SiO2% content of basic

45 - 52%

SiO2% content of intermediate

52-63%

SiO2% content of acidic

66%

A volcanic Ultramafic rock

Komatiite

A plutonic ultramafic rock.

Peridotite

A plutonic mafic rock

Gabbro

A volcanic mafic rock.

Basalt

A plutonic, salt and pepper colored rock

Diorite

A volcanic, gray colored rock

Andesite

A plutonic, light-colored (felsic) rocks, containing approximately two-thirds SiO2

Granodiorite

A volcanic, light-colored (felsic) rocks, containing approximately two-thirds SiOz,

Dacite

A plutonic, light-colored (felsic) rocks containing more than two-thirds SiO, (silicic or acidic)

Granite

A volcanic, light-colored (telsic) rocks containing more than two-thirds SiO, (silicic or acidic)

Rhyolite

Light-colored, felsic, frothy, vesicular rock.

Pumice

Dark-colored, mafic, frothy, vesicular rock.

Scoria

A dark-colored, silicic, non-crystalline igneous rock that has a glassy texture.

Obsidian

A dark-colored, basic, non-crystalline igneous rock that has a glassy texture.

Tachylite

INTRUSIVE IGNEOUS STRUCTURES (IIS): Plutons of more or less irregular shape with surface exposures ≥ 100 square kilomemetres.

Batholith

INTRUSIVE IGNEOUS STRUCTURES (IIS): Plutons with surface exposures ≤ 100 square kilometres.

Stocks

Intrusive Igneous Structures: Concordant Plutonic Structures A tabular, concordant pluton that parallels the country rock.

Sill

Intrusive Igneous Structures: Concordant Plutonic Structures A dome-like concordant pluton characterized by a dome roof and flat floor.

Laccolith

Intrusive Igneous Structures: Concordant Plutonic Structures A dish-shaped concordant pluton that has a “champagne glass” appearance in a section view.

Lopolith

Fractured rocks along a magma chamber’s wall.

Stopes

Consists of genetically-related magmas with a composition that evolved from a common, original, parental magma.

Magma Series

Record a progressive decrease in iron and magnesium with increasing SiO₂, and alkali concentrations due to the early crystallization of ferromagnesian minerals, hence, an enrichment in alkaline minerals. Produce largely andesites, dacites, rhyolites, and high-alumina basalts (BADR). Dominantly occurs along convergent margin environments with volcanic arcs and subduction zones.

Calc-Alkaline Magmas

Experience enrichment in iron at low to moderate SiO2 concentrations with increasing fractionation due to depleted MgO and CaO from early crystallization of forsterite olivine and Ca-plagioclase. Produce large volumes of basalt with little variations in composition. Dominantly occurs extensional environments such as ocean ridges and continental rifts, and some hotspots in intraplate settings and immature arcs in thin volcanic arc crusts.

Tholeiitic Magmas

Magmas that are less common than calc-alkaline or tholeiitic magmas, highly enriched in Na₂O and/or K₂O and contains an extremely diverse compositions that have SiO₂ contents ranging from 0-65%. Occurs in a wide variety of environments that include stable cratons, continental rifts and subduction zones.

Alkaline Magmas

Characterized by high concentrations of silicic and basic rocks, with little intermediate rocks, and associated with continental rifts. Its basic component is derived from partial melting of the mantle, while its silicic component is derived from the partial melting of the continental crust from the heating of the rising basic magmas.

Bimodal Magma Suites