Earth Mat Flashcards - Ch 15
Metamorphism refers to predominantly solid state mineral and/or textural changes to a pre-existing “ parent ” rock, or
protolith
results from increasing temperature and/or pressure conditions over time
Prograde metamorphism
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
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
serve as catalysts in retrograde metamorphism
Volatile components
involves the use of mineral assemblages or deformation characteristics of specific minerals to infer peak temperature and/or pressure conditions of metamorphism.
Geothermobarometry
A mineral assemblage of a metamorphic rock stable at current PTt is represented by an equilibrium assemblage
equilibrium assemblage
The onset of metamorphism begins at
~150–200°C.
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
occurs when the bulk composition of rocks changes as a result of chemical reactions with hot fluids of variable origin
Hydrothermal alteration
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
High temperature alteration resulting in Na enrichment
Albitic
Albite, paragonite (Na - rich mica)
Occurs in hot spring environments and gold and copper porphyry deposits by the oxidation of sulfide minerals
Alunitic
Alunite and sulfate minerals
Low temperature decomposition of feldspars in acidic (low pH) conditions; occurs in gold deposits hosted by sedimentary rocks; clays
Argillic
Kaolinite, smectite, illite
Replacement by carbonate minerals at variable temperatures
Carbonatization
Decomposition of silicic rocks; associated with porphyry copper deposits
Phyllic
Sericite, quartz, pyrite
High temperature alteration of silicic magma resulting in K enrichment; commonly underlies phyllic zones
Potassic
Biotite, K - feldspar, adularia
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
Alteration of feldspars
Sericitic
Sericite (fine - grained, white mica)
Low temperature alteration of basic and ultrabasic rocks
Serpentinization
Serpentine, talc
Replacement by silica minerals at variable temperatures
Silicification
Quartz, chert
Low temperature alteration of Ca - plagioclase to albite
Spilitization
Albite
Low temperature replacement of glass in volcanic rocks
Zeolite
Zeolite minerals
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
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
