Earth Mat Flashcards - Ch 15 Flashcards by Bien Mendoza

Metamorphism refers to predominantly solid state mineral and/or textural changes to a pre-existing “ parent ” rock, or

protolith

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results from increasing temperature and/or pressure conditions over time

Prograde metamorphism

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Devolatilization processes are particularly important in convergent margins where the loss of volatiles results in:

loss of highly mobile volatile components
Enhanced melting by an influx of volatiles
generation of high temperature anhydrous minerals

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results from decreasing temperature and/or pressure so that lower temperature/pressure mineral assem blages develop that overprint earlier peak temperature/pressure mineral assemblages.

Retrograde metamorphism

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serve as catalysts in retrograde metamorphism

Volatile components

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involves the use of mineral assemblages or deformation characteristics of specific minerals to infer peak temperature and/or pressure conditions of metamorphism.

Geothermobarometry

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A mineral assemblage of a metamorphic rock stable at current PTt is represented by an equilibrium assemblage

equilibrium assemblage

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The onset of metamorphism begins at

~150–200°C.

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a set of sedimentary processes that occur at temperatures less than ~ 150 – 200 ° C and at relatively low pressures (< 3 kbar or 10 km depth).

Diagenesis

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occurs when the bulk composition of rocks changes as a result of chemical reactions with hot fluids of variable origin

Hydrothermal alteration

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Volatile sources consist of:

“ Juvenile ” fluids derived from magma,
Seawater, which infi ltrates fractures and pore spaces
Fluids derived by devolatilization reactions, releases
H2O from amphibole, mica and serpentine minerals.
CO2 from limestone and dolostone
Meteoritic fluids
Connate fluids

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High temperature alteration resulting in Na enrichment

Albitic
Albite, paragonite (Na - rich mica)

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Occurs in hot spring environments and gold and copper porphyry deposits by the oxidation of sulfide minerals

Alunitic
Alunite and sulfate minerals

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Low temperature decomposition of feldspars in acidic (low pH) conditions; occurs in gold deposits hosted by sedimentary rocks; clays

Argillic
Kaolinite, smectite, illite

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Replacement by carbonate minerals at variable temperatures

Carbonatization

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Decomposition of silicic rocks; associated with porphyry copper deposits

Phyllic
Sericite, quartz, pyrite

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High temperature alteration of silicic magma resulting in K enrichment; commonly underlies phyllic zones

Potassic
Biotite, K - feldspar, adularia

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Low to moderate temperature decomposition of basic and ultrabasic rocks enriched in pyroxene, amphibole, biotite and plagioclase; also occurs in gold and copper porphyry deposits

Propylitic
Chlorite, epidote, actinolite, tremolite

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Alteration of feldspars

Sericitic
Sericite (fine - grained, white mica)

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Low temperature alteration of basic and ultrabasic rocks

Serpentinization
Serpentine, talc

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Replacement by silica minerals at variable temperatures

Silicification
Quartz, chert

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Low temperature alteration of Ca - plagioclase to albite

Spilitization
Albite

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Low temperature replacement of glass in volcanic rocks

Zeolite
Zeolite minerals

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reactions involve reactions in which igneous rocks are “stewing in their own juices.”
Hot, vapor-rich fluids are commonly associated with igneous intrusions that provide the heat, fluid, and corrosive compounds to chemically alter minerals.

Deuteric

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involves changes in solid rock composition resulting from hydrothermal fluids exchanging constituents with an outside source

Metasomatism

Uniform (isotropic) stress tend to produce metamorphic rocks with:

Equant grains Non foliated textures

Non - uniform stress is not equal in all directions and tends to produce metamorphic rocks containing

Inequant grains Foliated textures

such protoliths include aluminum - rich rocks such as shale, mudstone and altered volcanic tuff (bentonite).

Pelite

The aluminous polymorph minerals kyanite, andalusite and sillimanite are useful temperature and pressure indicators –_________ – based on their respective mineral stability field

geothermobarometers

commonly develop from mud stone protoliths.

slates, phyllites and mica schists

Contact metamorphism of pelitic protoliths produces

non - foliated Hornfels

commonly occurs with andalusite in low pressure assemblages

Cordierite

____________ protoliths include quartz sandstone, arkosic sandstone and intermediate to silicic igneous rocks such as granite, granodiorite and their volcanic, equivalents.

Quartzofeldspathic or psammitic

_______ protoliths include carbonate sedimentary rocks such as limestone and dolostone

Calcareous

in calcareous rocks ________ may form under high pressure conditions,

lawsonite and coesite

include igneous rocks such as basalt, andesite, diorite and gabbro.

intermediate to basic

zeolite, pumpellyite, chlorite,chrysotile serpentine and epidote occur in

low temperature/low pressure environments

Glaucophane, lawsonite, jadeite, crossite and riebeckite occur in

low temperature/ high pressure rocks

include pyroxenites and peridotites.

Ultrabasic protoliths

OSHA defines asbestiform minerals

Filiform minerals length > 5 micrometers diameter < 5 micrometers length : width ratio > 3:1 Fibrous length : width ratio > 10:1

two groups of asbestiform minerals

Serpentine/Chrysotile Amphibole

AKA White asbestos Soft, curly, flexible fivers 95% global supply

serpentine/Chrysotile

Around `5% of global asbestos Hard and Brittle

Amphibole Asbestos

Amphibole Asbestos varieties

Crocidolite Amosite Anthophyllite Actinolite Tremolite

blue asbestos; variety of riebeckite

Crocidolite

brown asbestos; variety of grunerite

Amosite

A disease whereby lung tissue encapsulates asbestos particles. As a result, lung tissue hardens and decreases essential O₂/CO₂ exchange. This effect weakens the heart and destroys the lungs.

Asbestosis

A rare disease of the lining of the lung and stomach caused by asbestos.

Mesothelioma

All abestos minerals are equally hazardous?

No. In fact, the most widely used chrysotile fibers decompose naturally within the lungs over a period of 9 months. As a result, the three diseases listed above are not generally associated with chrysotile asbestos. In contrast, the less widely used amphibole asbestos minerals do not decompose over the course of decades and are a serious health hazard.

is a **low temperature, brittle grain - fracturing** process that involves' *grain size reduction** through the mechanical grinding, rotation and crushing of rock

Cataclasis

is a **ductile grain reduction** process that produces oriented grains of smaller diameter

Mylonitization

Mylonitzation occurs in

occurs in high temperature, high strain shear zones of the **lower crust and upper mantle.**

occurs in metamorphic rocks whereby individual atoms or molecules can migrate in gaseous, liquid or solid phases from one location in a rock body to a new location.

Diffusion

diffusion is facilitated by _____________ And by presence of small amounts of ____________ that catalyze chemical reactions

crystal dislocations; intergranular fluids

involves the dissolution of solid grains under high compressive stress conditions.

Pressure solution (pressolution)

soluble minerals dissolve, insoluble minerals (iron oxides, micas, graphite) accumulate as an insoluble seam called a

stylolite

occurs when existing minerals are transformed under higher temperature and/or pressure conditions, **without experiencing a significant change in chemical composition**

Recrystallization

Extracrystalline recrystallization

Grain rotation, grain boundary migration Addition/removal of mineral material by diffusion

Intracrystalline recrystallization

Within individual grains due to microscopic movements related to defects, vacancies or dislocations Recovery is a means by which crystal defects are minimized by the movement of ions within a grain. Permanent, plastic process; does not involve visible breakage

refers to the nucleation and growth of new minerals as pre-existing minerals become unstable due to temperature/pressure changes.

Neocrystallization

In the context of neocrystallization, newly formed minerals distinctly larger than the minerals in the surrounding matrix are referred to as

porphyroblasts

refers to the segregation of minerals in an initially homogeneous rock due to different physical or chemical characteristics such as solubility, ductility, mineral growth or crystallization temperature.

Differentiation

In the context of metamorphic differentiation, less soluble minerals (e.g., ferromagnesium minerals and clays) occur in

concentrated in fold hinges,

In the context of metamorphic differentiation, soluble minerals (e.g., calcite, quartz and feldspars) are

fold limbs.

Through differentiation, more competent (rigid) porphyroblast minerals such as garnet, quartz or feldspars can extend and grow, producing elongated forms This producess _________________ about which more ductile minerals such as micas can accumulate and grow

pressure shadows

Metamorphism occurs on a variety of scales. __________ metamorphism affects areas of less than 100 km^2 __________metamorphism affects areas greater than 100 km2

Local; Regional

is generated by explosive volcanic eruptions or relatively rare collisions of extraterrestrial objects with Earth.

Impact metamorphism

produces breccias, shocked quartz lamelle, pseudotachylites produced by impact melting and ultra high pressure (UHP) minerals (like coesite and stishovite)

Associated high strain rate

rocks produced by impact metamorphism

Impacttites

is induced primarily by non - uniform stress in fault zones and shear zones

Dynamic metamorphism

Characteristics of dynamic metamorphism

High strain rate; local extent mostly Short time intervals High likelihood of recurring at the same fault/shear zone

are fragmented rocks that have experienced the breakage of brittle rock into smaller sized fragments.

Cataclasites

are partially melted rocks that form by quenching under high strain rates in shear zone fractures.

Pseudotachylites

deform plastically producing mylonite rocks. zones of ductile deformation at depths greater than ~10–15 km

Ductile shear zones

are characterized by grain size reduction via microscopic scale cataclasis, plastic stretching and thinning associated

Mylonites

evelops locally where hot magma intrudes relatively cold, upper crustal ( < 10 km) country rock.

Contact metamorphism d

is a general term for fine - grained, contact metamorphic rock rich in silicate minerals

Hornfels

develop when igneous plutons intrude carbonate rocks

Skarns

Common calc-silicate minerals produced by contact metamorphism of carbonate include

wollastonite, tremolite, grossular garnet, spessartine garnet, and andradite garnet.

Serpentinization occurs when

magnesium - rich olivine or pyroxene minerals are altered to serpentinite by seawater - derived hydrothermal fluids.

Spilitization occurs as a result of

the exchange of sodium from seawater for calcium in plagioclase, which converts the plagioclase into albite.

is the name for sodium - rich basalts that form along ocean ridges and volcanic arcs.

Spilite

results from increases in lithostatic stress induced by deep burial of rock and produces non - foliated textures

Burial metamorphism

is a regional metamorphism induced by increases in both pressure and temperature.

Dynamothermal metamorphism