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Kinds of metamorphism. Lecture based on http://csmres.jmu.edu/geollab/Fichter/MetaRx/MetaKind.html And PowerPoint lecture of Dr. J.D. Winter http://www.whitman.edu/geology/winter/. The Types of Metamorphism. Different approaches to classification. 1. Based on principal process or agent

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kinds of metamorphism

Kinds of metamorphism

Lecture based on http://csmres.jmu.edu/geollab/Fichter/MetaRx/MetaKind.html

And PowerPoint lecture of Dr. J.D. Winterhttp://www.whitman.edu/geology/winter/

slide2

The Types of Metamorphism

Different approaches toclassification

  • 1. Based on principal process or agent
    • Dynamic Metamorphism
    • Thermal Metamorphism
    • Dynamo-thermal Metamorphism
slide3

2. Based on setting (P-T conditions/tectonic)

    • Contact Metamorphism
      • Pyrometamorphism
    • Regional Metamorphism
      • Orogenic Metamorphism
      • Burial Metamorphism
      • Ocean Floor Metamorphism
    • Hydrothermal Metamorphism
    • Fault-Zone Metamorphism (cataclastic or mylonitic in your text)
    • ImpactorShockMetamorphism
types of metamorphism based on pressure and temperature conditions
Types of metamorphism based on pressure and temperature conditions

http://csmres.jmu.edu/geollab/Fichter/MetaRx/MetaKind.html

blueschist metamorphism

Geothermal gradient: Indicates the average increase of temperature with depth

Blueschist metamorphism
  • HIGH pressure/Low temperature
  • Typically associated with subduction zones
  • Example: Blueschist (from glaucophane)
slide6

1mm

Glaucophane in a blueschist (ppl).

http://www.union.edu/PUBLIC/GEODEPT/COURSES/petrology/met_minerals.htm#Amphiboles

eclogite metamorphism
Eclogite metamorphism
  • VERY HIGH pressure/moderate temperature
  • Happens in the mantle
  • Example: Eclogite (pyroxene/garnet)
slide8

Eclogite (xpl)

Eclogite (ppl)

hydrothermal metamorphism
Hydrothermal metamorphism
  • Low pressure/low temperature
  • Hot, chemically active waters react with the surrounding rocks
  • Example: Serpentinite, soapstone
hydrothermal metamorphism10
Hydrothermal metamorphism
  • Usually involves METASOMATISM (metamorphism plus exchange of ions from an external source)
  • Difficult type to constrain: hydrothermal effects often play some role in most of the other types of metamorphism
contact metamorphism
Contact metamorphism
  • Low pressure/HIGH temperature
  • “Country” rocks baked by igneous intrusion (pluton)
  • Example: Hornfels, skarn (baked carbonate rocks), quartzite, marble
slide13

Contact Metamorphism

Most easily recognized where a pluton is introduced into shallow rocks in a static environment

(Pluton=intrusive igneous body, like a batholith)

  • ®Hornfelses (granofelses) commonly with relict textures and structures
spotted hornfels
Spotted hornfels

http://www.geolab.unc.edu/Petunia/IgMetAtlas/meta-micro/spottedhornfels.X.html

slide15

Pyrometamorphism

A minor type of contact metamorphism

Very high temperatures at very low pressures, generated by a volcanic or subvolcanic body

Also developed in xenoliths (pieces of solid rocks carried up by magma)

Pyrometamorphism may be accompanied by various degrees of partial melting

barrovian metamorphism
Barrovian metamorphism

Also referred to as “regional” metamorphism

  • Intermediate pressure/Low-high temperature
  • Example: Slate-phyllite-schist-gneiss, also quartzite and marble
slide17

Regional Metamorphismsensu lato: metamorphism that affects a large body of rock, and thus covers a great lateral extent

  • Three principal types:
    • Orogenic metamorphism
    • Burial metamorphism
    • Ocean-floor metamorphism

The term, “regional metamorphism” is often used synonymously with “orogenic metamorphism” (OROGENY=mountain building)

slide18

Orogenic Metamorphism is the type of metamorphism associated with convergent plate margins

  • Dynamo-thermal: one or more episodes of orogeny with combined elevated geothermal gradients and deformation (differential stress)
  • Foliated rocks are a characteristic product
slide19

Foliation

Slate (ppl)

Phyllite (xpl)

Quartz

Muscovite

Quartz-muscovite schist (xpl)

http://www.geolab.unc.edu/Petunia/IgMetAtlas/meta-micro/metamicro.html

slide20

Crenulation cleavage in a muscovite-biotite-garnet schist (xpl)

http://www.geolab.unc.edu/Petunia/IgMetAtlas/meta-micro/metamicro.html

slide21

Gneiss under a microscope (xpl)

Biotite

Feldspar

Quartz

Gneiss in hand specimen

http://www.geolab.unc.edu/Petunia/IgMetAtlas/meta-micro/metamicro.html

slide23

Burial metamorphism=low-grade metamorphism in sedimentary basins

    • Metamorphic effects attributed to increased temperature and pressure due to burial
    • Occurs in areas that have not experienced significant deformation or orogeny
    • Mild deformation, no igneous intrusions discovered
slide24

Restricted to large, relatively undisturbed sedimentary piles away from active plate margins

    • Term coined by Coombs (1961) based on Southland Syncline in New Zealand: thick pile (> 10 km) of Mesozoic volcaniclastics
    • Modern examples:
    • The Gulf of Mexico?
    • Bengal Fan?
slide25

Ocean-Floor Metamorphismaffects the oceanic crust at ocean ridge spreading centers

  • A wide range of temperatures at relatively low pressure
  • Seawater penetrates down fracture systems, where it becomes heated, and leaches metals and silica from the hot basalts
  • Considerable metasomatic alteration, notably loss of Ca and Si and gain of Mg and Na
slide26

Highly altered chlorite-quartz rocks- distinctive high-Mg, low-Ca composition

Black smokers - Another example of hydrothermal metamorphism

slide27

Fault-Zone and Impact Metamorphism

    • High rates of deformation and strain with only minor recrystallization

(a) Shallow fault zone with fault breccia

(b) Slightly deeper fault zone (exposed by erosion) with some ductile flow and fault mylonite

slide29

Fault-Zone and Impact Metamorphism

    • High rates of deformation and strain with only minor recrystallization
  • Impact metamorphism at meteorite (or other bolide) impact craters
  • Both correlate with dynamic metamorphism, based on process