Earth Mat Flashcards - Ch 8 Flashcards by Bien Mendoza

Solidify to produce igneous rocks in Earth’s crust are initially formed by a process called ___, which refers to the partial melting of a source rock.

anatexis

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Anatexis produces:

A liquid melt fraction enriched in lower temperature constituents.
A residual rock component enriched in higher temperature, refractory elements.

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In the simplest approach, rock melting within Earth’s interior is modeled as two idealized end-member processes:

equilibrium melting and disequilibrium (fractional) melting.

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occurs in a closed system where chemicals are neither added nor removed from the plutonic environment.
requires that the melt remains in contact with the residual rock throughout the melting process.

Equilibrium melting

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Incomplete chemical reactions may be due to

large crystal size, high magma viscosity, and/or low ion migration rates.

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The net result of inequilibrium melting is the generation of

zoned crystals

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Cause of Fractional (disequilibrium)melting

melts are separated from the refractory crystals, liquids and crystals do not remain in equilibrium

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what happens in fractional melting of rocks containing plagioclase and olivine

The early melts are highly enriched in low melting temperature constituents, such as sodium plagioclase and iron olivine.
This leaves behind a more refractory residual solid enriched in calcium plagioclase and magnesium olivine.

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Pressure is related to rock depth, whereby 10 km depth corresponds approximately to

3.3 kbars.

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is the primary means by which basaltic magmas are generated at ocean spreading ridges and continental rifts.

Decompression melting of mantle peridotite

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Volatiles act as a ____, which is an agent that reduces the melting temperature of a substance.

flux

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As the degree of partial melting increases, the degree of enrichment of incompatible elements ________.

decreases

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Light rare earth elements (LREE) are generally less incompatible with solid minerals than heavy rare earth elements (HREE).
T or F

F; more incompatible

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processes involve changes in bulk magma chemistry after its initial generation.

Diversification

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includes all processes where the original melt evolves into one or more melts with a different composition, without material being exchanged with an external source.

Closed-system diversification

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Father of Modern petrology

Norman Bowen

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The subject of study in Bowens reseach

Palisades Sill

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When discontinuous and continuous reactions in magmas do not reach completion under equilibrium, chemical variations are preserved in crystals, leading to the formation of

zoned crystals and reaction rims.

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show a systematic chemical variation from the core to the edge, recording incomplete continuous reactions between the crystal and surrounding melt.

Zoned crystals

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occur when a new mineral forms around the edges of a crystal with a partially resorbed core.

Reaction rims

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Crystallization along the walls of the magma chamber in which crystals preferentially form and adhere to the edges results in

marginal accretion.

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Heat rises so that the upper margin of the magma chamber may cool relatively quickly.
As a result, __________ results from early crystallization of minerals along the ceiling or roof due to preferential heat loss.

roof accretion

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___________develops as the magma chamber walls release heat to the relatively cold country rock, generating crystals that adhere to the side margins of the magma chamber.

Sidewall accretion

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occurs as crystals form along the base of the magma chamber.

Floor accretion

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Because they lose heat rapidly to the wall rocks, pluton margins adjacent to cool country rock commonly display finer grained ____________ compared to the coarser grained crystals of the pluton interior.

chilled margins

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

Gravitational separation

occurs when higher density, ferromagnesian crystals settle to the base of a magma chamber relative to the lower density liquid magma.

Crystal settling

can occur if early formed crystals, such as plagioclase, are less dense than the magma. As a result, crystals may float towards the roof of a magma chamber, effectively segregating them from the remaining melt.

Crystal flotation

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

Convective flow

Cooling can be accompanied by deformation whereby crystals are compacted and rotated while liquids experience expulsion. This variation on crystal–liquid fractionation involves a set of processes under the umbrella of

filter pressing.

In _________, one parent magma fractionates to produce two or more distinctly different daughter magmas with different compositions.

liquid fractionation

Liquid fractionation processes include

differential diffusion and liquid immiscibility.

involves the preferential diffusion of select ions within the magma in response to compositional, thermal, or density gradients as well as water content.

Differential diffusion

also called liquid–liquid fractionation, occurs when magma separates into two or more distinct immiscible liquid phases.

Liquid immiscibility,

How does carbonitite form

CO₂ exsolves as a separate fluid phase from alkalic magmas, generating a carbonate-rich fluid which crystallizes as a carbonatite.

processes such as assimilation, magma mixing, and magma mingling involve chemical changes due to interaction of magma with the surrounding country rock or with other magmas entering the system

Open-system

occurs whereby the surrounding wall rock (country rock) is intruded by and reacts chemically with the magma.

Assimilation

Forceful injection of magma commonly fractures the surrounding wall rock by a process called .

stoping

involving multiple magma injections over time, produces complex relationships and constitutes an important diversification mechanism.

Magma replenishment,

occurs when two or more dissimilar magmas coexist, displaying contact relations but retaining their distinctive individual magma characteristics.

Magma mingling

implies thorough mixing so that the individual magma components are no longer recognizable.

Magma mixing

consists of genetically related magmas that have changed composition from a common original parental magma

magma series

Igneous rock series include:

(1) alkaline (or alkalic), and (2) sub-alkaline assemblages.

have high Na₂O and K₂O concentrations compared to SiO₂ and are generally undersaturated with respect to SiO₂.

Alkaline rocks

rocks have moderate to high Na₂O, K₂O, and SiO₂ concentrations.

Calc-alkaline

have low Na₂O and K₂O but high FeO and CaO concentrations.

Tholeiites

provide a means to concisely and clearly display rock chemistry variations between samples collected in an area with an eye to establishing their origins and relationships.

Variation diagrams

are bivariate diagrams in which the vertical ordinate (y-axis) represents weight percents of major or minor oxide compounds such as FeO, MgO, CaO, Na₂O, K₂O, or TiO₂.

Harker diagrams

If Harker diagrams display smooth, curvilinear trends for all rock data points, then the following three inferences can be made:

The rocks are genetically related. Major element variations reflect a liquid line of descent from a common source in which diversification caused major elements to either increase or decrease progressively with respect to variations in weight percent SiO₂. The parent magma from which the rocks are derived has a composition near that of the sample with the least SiO₂, that is, of basaltic composition

In ____________ trace element concentrations on the abscissa are plotted relative to a standard reference for each element on the ordinate.

spider diagrams,

The standard reference of spider diagrams may include

* chondrite meteorites, * primitive mantle, * N-MORB * E-MORB * ocean island basalt

depletion of europium indicates

plagioclase fractionation from the melt, which effectively removes europium from the magma.

europium enrichment would indicate

assimilation of plagioclase components into the melt.

Upon fractionation, ____ magmas record a progressive decrease in iron and magnesium with increasing SiO₂ and alkali concentrations

calc-alkaline

The calc-alkaline series consists largely of

andesite, dacite, and rhyolite, as well as high alumina basalt (16–20% Al₂O₃) (BADR series)

The rocks in convergent margin volcanoes are known colloquially as

BADR series for the basalts, andesites, dacites, and rhyolites that occur in them.

With increasing fractionation, **tholeiitic** magmas experience _at low to moderate SiO₂ concentrations

iron enrichment

**Alkaline** magmas and rocks are highly enriched in _______________ and are less common than calc-alkaline or tholeiitic magmas.

Na₂O and/or K₂O

Alkaline rocks can contain equilibrium quartz.

FALSE

Amphibole minerals in alkaline magmas include

riebeckite and richterite.

Pyroxene minerals found in alkaline rocks include

aegerine, aegerine-augite, and spodumene.

Alkaline rocks occur in diverse environments:

Stable cratonic interiors Continental rifts (Bailey, 1974) Ocean islands away from spreading centers (Sorensen, 1974) Subduction zones (Burke et al., 2003

Tholeiitic magmas are typically produced by

extensive partial melting of mantle rocks at relatively higher temperatures and lower pressures, often from a **depleted source**

Alkaline magmas are more likely to form through ______________________________ particularly from an **undepleted or enriched mantle source**

**limited partial melting (less than 10%)** of the mantle at higher pressure conditions

consist of large amounts of both silicic (rhyolite-dacite) and basic (basalt) rocks, but have very few intermediate (andesite) rocks.

Bimodal suites

The tectonic environments where magma series occur in summary

**Calc-alkaline** magmas: Convergent margins. **Tholeiitic** magmas: Ocean spreading centers, continental rifts, backarc basins, ocean islands, and hotspots. **Alkaline magmas**: Hotspots, ocean islands, and rift environments. **Bimodal** volcanism: Continental rifts.

is the major mechanism by which continental crust has grown since the Archean, over 2.5 billion years ago

Batholith emplacement along convergent plate boundaries

Normal zoning within a pluton is characterized by a

basic rim and a silicic core.

A ___________ is a tabular, concordant pluton that parallels country rock

sill

Sills develop through ____

the injection of magma along a plane (e.g., bedding, foliations) of weakness parallel to the layering in the country rock.

Sills commonly form in__________ magmas and are generally _________ in thickness.

low-viscosity; < 50m

is a blister-like concordant pluton characterized by a flat floor and domed roof

A laccolith

Laccoliths were first described in the _of Utah by G. K. Gilbert in the 1870s.

Henry Mountains

are dish-shaped to funnel-shaped concordant plutons that resemble a champagne glass in cross-section view

Lopoliths

The Bushveld Complex has a length of ___ and is up to_____ thick.

550 km; 8 km

The champagne-glass lopolith structure can develop due to one or more of the following mechanisms:

Meteorite impact and associated crustal melting, as has been suggested for the Sudbury Complex. Normal faulting and crustal melting associated with rifting, as in the Koillismaa Complex. A sill-like structure that receives upwelling magma from a conical feeder tube, which would correspond to the stem in the champagne glass.

Veins can occur in great abundance, resulting in

vein swarms.

are cylindrical plutonic dikes exposed at the surface by subsequent erosion. They represent ancient ______________________ that has long since been removed by erosion.

Necks conduit pipes that funneled magma upward to a volcano

Notable examples of volcanic necks include _______________ which has a central neck with radiating dike ridges, and _______ , which preserves radial columnar jointing.

Ship Rock, New Mexico,; Devil’s Tower of Wyoming

are carrot-shaped, cylindrical pipes that can extend to depths of 200 km (Figure 8.19). develop via _____________________

Diatremes; explosive intrusions that originate deep within the mantle.

are tabular intrusions that cross-cut country rock layers.

Dikes

consist of multiple dikes that can occur in parallel, sub-parallel, radiating, concentric, or random orientations.

Dike swarms

are typically produced when vertical forces related to rising magma produce fractures that radiate outward from the central vent.

Radial dikes

are circular in map view and resemble ring dikes, except that they **converge** at depth in cross-section view.

Cone sheet dikes

sets consist of parallel, offset dikes that form in response to shear.

En echelon dike

sets form perpendicular to extension and are particularly common in rift environments.

Parallel dike

Steeply inclined _________________, composed of gabbro, diabase, and basalt, form layer 2B of the ocean floor at ocean spreading ridges (Figure 8.23).

sheeted dikes

Sheeted dikes form by the

cooling and contraction of magma as it is injected into extensional fractures in oceanic rift valleys.