Questions or comments? mailto:warburto@fau.eduGLY 4310C
WORD LIST FOR FINAL EXAMINATION
The final examination will be given on Friday, April 30, 2010 7:45 a.m. - 10:15 a.m. The test will concentrate on material from chapters 21, 22, and 25 of Winter, but will include a review of material from the entire course. Homework 4 will also be tested. You should bring a calculator to the exam.
Definition of metamorphism-classic
Boundary with diagenesis
Minerals characteristic of onset of metamorphism
Boundary with magma
Protolith
IUGS-SCMR
Definition of metamorphism
Substances excluded from treatment as metamorphosis
Agents of Metamorphism
Temperature
Promotes recrystallization
Devolatilization reactions
Crystallization reactions
Kinetic barriers
Mineralizers
Pressure
Continental geotherm
Oceanic geotherm
Metamorphic field gradients (aka Metamorphic trajectories)
Metamorphic grade
Lithostatic pressure, σ1=σ2=σ3
Deviatoric Stress
Stress tensor
Principle components - σ1, σ2, σ3
Strain ellipsoid
Tension - σ1>σ2>σ3 , σ3 = negative
Fractures perpendicular to σ3
Compression
Folding, σ1>σ2>σ3
Flattening, σ1>σ2≈σ3, (Simple shear)
Foliation and lineation resulting from compression in two directions
σ1>σ2=σ3, Foliation, no lineation
σ1=σ2>σ3, Lineation, no foliation
σ1>σ2>σ3, Both foliation and lineation
Shear
Pure shear - foliation ⊥ to short axis of deformation
Simple shear - foliation not orthogonal to short axis of deformation
Metamorphic fluids
Water
Critical Point
Evidence for composition
Planar array of fluid inclusions = post metamorphic
Relationship between Plith and Pfluid
Plith = ρmineralgh
Pfluid = ρwatergh
ρmineral > ρwater, ∴ Plith >Pfluid
If Plith >>Pfluid, then:
Mineral grains deform, compressing pore space, or
Pressure solutioning occurs
Relationship between total fluid pressure and its components
PH2O = XH2O ●Pfluid
Potential fluid sources
Meteoritic water
Juvenile water
Water associated with subducted material
Sedimentary brines
Water from metamorphic dehydration reactions
Degassing from the mantle
Metasomatism
Fluids hot and under pressure
Chemical exchange
Types of metamorphism - know agents, locations
Contact metamorphism
Contact aureole - size
Affect of metasomatism
Reaction with carbonates to produce skarns or tactites
Hornfels
Granofels
Pyrometamorphism
Regional metamorphism
Orogenic
Orogenic welt
Tectonic underplating
Magmatic underplating
Gneiss domes, or metamorphic core complexes
Polymetamorphic imprint
Burial
Implication of vein metamorphism
Lack of structural deformation
Ocean-floor metamorphism
T varies widely, P low
Substantial local variations in degree of metamorphism
Most metamorphism occurs very near the ridge
Alternate name - Ocean-ridge metamorphism
Spillite
Faut-zone metamorphism
AKA dislocation metamorphism, shear-zone metamorphism
Strain in crystal lattices lowers kinetic barriers
Cataclasis
Fault breccia
Fault gouge
Impact metamorphism
Presence of high-pressure silica phases - coesite, stishovite
Shocked quartz crystals - shock lamellae
Shatter cones
Progressive metamorphism - equilibrium maintained throughout ongoing changes
Prograde - results from increase in temperature, pressure, or both
Endothermic
Cause devolatization
Retrograde - results from decrease in temperature, pressure, or both
Exothermic
Hindered by previous loss of volatiles
Geothermobarometry
Exchange reactions
Prolith types - know characteristic chemistries, rock types
Ultramafic - Very high Mg, Fe, Ni, Cr
Mafic - High Mg, Fe, Ca
Pelitic - High Al, K, Si
Calcareous - High Ca, Mg, CO2
Quartz - High SiO2
Quartzo-feldspathic rocks - High Si, Na, K, Al
Mixture - psammitic
Exceptions - evaporites, iron-stones, phosphates, alkaline igneous rocks, coal and other organic-rich rocks, manganese sediments, and ore bodies
Examples of metamorphism
Orogenic regional metamorphism, Scottish Highlands
George Barrow
Barrovian metamorphic zones - High P/T
Chlorite - slates, phyllites
Biotite - Phyllites, schists
Garnet - Garniferous schists
Staurolite - Schist
Kyanite - Schist
Sillimanite - Schists and gneisses
Isograd - C..E. Tilley
Persistence of minerals beyond their regions of stability
Zones in Buchan and Abukuma type localities - Low P/T
Chlorite
Biotite
Cordierite
Andalusite
Sillimanite
Cordierite and andalusite are low-P minerals
Regional Burial Metamorphism - Otago, New Zealand
Isograds
Zeolite
Prehnite-pumpellyite
Pumpellyite(-actinolite)
Chlorite(-clinozoisite)
Biotite
Almandine garnet
Oligoclase
Presence of laumontite, prehnite, and pumpellyite imply CO2 free conditions
Paired Orogenic Metamorphic Belts, Japan
Abukuma or Ryoke belt - Buchan type, Low P/T
Sanbagawa belt - Higher P/T
Glaucophane
Belts separated by a major fault zone (Median Line)
Offset is dip-slip, with notable strike-slip component
Contact Metamorphism of Pelitic Rocks - Skiddaw Aureole, UK
Intruding body - granite to granodiorite
Isograds not useful, since mineralogy doesn’t change
Zones - structural, rather than grade
Outer - Spotted slate
Middle - Andalusite slate
Inner - Hornfels
Width of aureole suggests igneous contacts dip outward at a small angle
Comrie schists, Scotland
Intruding body - diorite
Inner aureole - granofels
Opx - highest grade in both regional and contact
Differences in mineral assemblages based on protolith, loss of fluidContact Metamorphism and Skarn formation, Crestmore, California
Contact Pyrometamorphism
Intruding body - quartz monzonite porphyry
Country rock - Mg-bearing carbonates, previously metamorphosed
Metamorphic zones and sub-zones
Clear progression of minerals
Appearance of index minerals is clear
What is actually happening in terms of chemistry?
Chemical reactions
Hard to determine
Provide additional information
Treat all isograds as chemical reactions when possible
Chemographic compatibility (aka composition-paragenesis) diagrams
Tie-lines
Choose end-members carefully
Volatiles usually omitted
Other oxides may need to be omitted - at Crestmore, Al2O3
At Crestmore, trend is increase in silica
Must come from fluids released by magma
Porphyries involve loss of volatiles
Metamorphic Terminology - Chapter 22
Foliation
Lineation
Rock cleavage
Schistoscity
Gneissose structure
Metamorphic rock names
Slate
Phyllite
Schist
Gneiss
Hornfels
Granofels
Marble
Quartzite
Greenschist
Amphibolite
Serpentinite
Blueschist
Eclogite
Skarn (or Tactite)
Granulite
Migmatite
Porphyroblast
Porphyroclast
Augen (sing. auge)
Ortho-
Para-
High-Strain Rocks
Non-cohesive
Fault breccia
Fault gouge
Cohesive
Non-foliated
Microbreccia
Cataclasite
Foliated
Protomylonite
Mylonite
Ultramylonite
Blastomylonite
Pseudotachylyte
Metamorphic Facies - Chapter 25
Pentii Eskola
Definition of metamorphic facies
Viktor Goldschmidt
Characteristics of and differences between Norwegian and Finnish hornfels
Eskola’s's Original Facies
Greenschist
Amphibolite
Hornfels
Sanidinite
Eclogite
Eskola's additional facies
Granulite
Epidote-amphibolite
Glaucophane Schist
Changed hornfels to pyroxene hornfels
Coombs additions
Zeolite
Prehnite-pumpellyite
Fyfe's additions
Albite-epidote hornfels
Hornblende hornfels
Facies groups
High pressure - Blueschist, eclogite
Medium pressure - Greenschist, amphibolite, granulite
Low pressure - Albite-epidote hornfels, hornblende hornfels, pyroxene hornfels, sanidinite
Low grade - Zeolite, prehnite-pumpellyite (sub-greenschist facies)
Facies Series
High P/T series
Medium P/T series
Low P/T series
Metamorphism of Mafic Rocks
Importance of hydration reactions
Exothermic
Lack of sufficient fluid may limit complete reaction
Breakdown of plagioclase and clinopyroxene
Peristerite solvus - An 7-17
Low P/T series facies
Zeolite Facies
Heulandite
Analcime
Laumontite - some petrologists believe this mineral marks the start of metamorphism
Prehnite
Pumpellyite
Wairakite
Prehnite-pumpellyite
Loss of laumontite marks transition to this facies
Pumpellyite-actinolite subfacies
Medium P/T series facies
Greenschist facies
Correlates with chlorite and biotite zones from pelitic rocks
Chlorite, actinolite, epidote give the characteristic green color
Characteristic mineral assemblage
Chlorite + Albite + Epidote + Actinolite + Quartz
Amphibolite facies
Marked by two changes from greenschist
Transition from albite to oligoclase across peristerite solvus
Transition from actinolite to hornblende
Albite-epidote amphibolite facies
Hornblende appears before oligoclase
Seen in high P/T terranes
Corresponds to garnet, staurolite, and kyanite zones from pelitic rocks
Characteristic mineral assemblage
Hornblende + Plagioclase + Quartz + Epidote + Garnet + Clinopyroxene + Biotite
(Epidote disappears in the upper amphibolite facies)
Cordierite-anthophyllite rocks, attributed to ocean-ridge metamorphism, belong to amphibolite facies
Granulite facies
Transition from amphibolite facies occurs between 650-800°C
Characteristic mineral assemblage
Orthopyroxene + Clinopyroxene + Plagioclase + Quartz + Garnet
Presence of a single pyroxene in an assemblage is not diagnostic of the granulite facies
Conditions necessary for granulite to form
Very hot temperatures
Anhydrous conditions
Origin of granulite facies rocks
CO<SUB>2</SUB> displaces water in fluid phase
Traditional view is of deep crustal burial with dehydration
Most are associated with deeply eroded Precambrian rocks in shield regions
Differences between amphibolite and granulite
Granulite facies are depleted in LIL and other incompatible ions
May be removed in aqueous phase generated by dehydration
May be removed in partial melt
Different facies formed from different protoliths
Albite-Epidote Hornfels, Hornblende Hornfels, Pyroxene Hornfels and Sanidinite Facies
Metabasites in these facies very similar to equivalent regional metamorphic facies
Differences
Formation of transitional zone, actinolite-calcic plagioclase
Pyralsite garnets absent
Ca-poor amphiboles are more common (cummingtonite)
Hot, dry intrusions necessary to produce pyroxene hornfels facies
Sanidinite facies does not occur with metabasites
Blueschist Facies
Strong association with subduction zones - high P/T ratio
Precambrian blueschists are rare - why?
No subduction in the Precambrian
Higher geothermal gradients - high P/T ratio unlikely
Later metamorphic events have completely overprinted early events
Presence of initial zeolite facies
Intermediate lawsonite-albite-chlorite facies possible
Blue color due to sodic amphibole
Usually glaucophane, sometimes riebeckite
Characteristic mineral assemblage
Jadeite + Quartz (high pressure blueschist)
Glauophane + Epidote (low pressure metabasites)
Jadeite + albite (low pressure, ultramafic protolith)
Eclogite facies
Characteristic mineral assemblage
Omphacite + garnet
Garnet may be almandine (Fe), grossularite (Ca) or pyrope (Mg)
Eclogite environments
Xenoliths in basalt or kimberlite
In migmatitic gneisses
In blueschist
Eclogite temperature ranges
Low 450°- 550°C - Pyrope content < 30%
Medium 550° - 900°C - Pyrope content 30-55%
High 900° - 1600°C - Pyrope content > 50%
Greater temperature range than any other facies
P-T-t (Pressure-Temperature-time) paths
Evidence
Overprints of one mineral assemblage on another
Geothermometry and geobarometry
Heat-flow models
Reverse vs. forward methods
Contributions to regional metamorphism
Crustal thickening
Extra radioactive heat from thickened crust
Heat generated by orogenic processes
Types of heat-flow models
Orogenic belt experiencing crustal thickening - clockwise
Shallow magmatism - clockwise
Types of granulite facies metamorphism -counterclockwise (isobaric cooling) or clockwise (isothermal decompression)
Parameters affecting models
Rate of crustal thickening
Rate of heat transfer
Degree of magmatism
Degree and rate of erosion ("unroofing")
Difficulties with granulite facies models
Prolonged high T conditions may allow retrograde reactions
Paths may be artifact of thermobaric techniques
Other counterclockwise paths
Buchan trajectory in eastern zone of Acadian orogeny
Lack of explicit representation of time in diagrams
Inferences from P-T-t path studies
P and T do not necessarily increase together
P and T maxima occur at different points on path
Metamorphic grade usually represents Tmax
Significant differences in reactions during cooling
Spatial changes in mineralogy do not correspond to temporal changes
Blueschist facies conditions may occur during regional metamorphism
Blueschist with greenschist/amphibolite overprints occur
Why aren't blueschists formed during regional metamorphism generally seen?
Initial rate or pressure increase may be too steep - no blueschist forms
Early, rapid uplift, necessary to preserve blueschist, is uncommon during regional metamorphism
Questions or comments? mailto:warburto@fau.edu
Last updated: April 16, 2010