What is “metamorphism” ? What is “metamorphism” ?

• transformation of pre-transformation of pre-existing existing rock from one to anotherrock from one to another throughthrough pressurepressure and and temperaturetemperature relationshipsrelationships

• metameta (change)(change) morphismmorphism (form)(form)

• all changes take place throughall changes take place through solid state transformationsolid state transformation

Types of Metamorphism• takes place around 150oC (temperature)(temperature) • typically at depths of 5 km below the earth’s surface (Pressure)(Pressure)

At this temperature and pressure new mineralsare formed – changed from one mineral to

another

Low-grade Metamorphism• between 5-15 km below the earth’s surface

• temperatures up to 400oC

• common low-grade minerals• quartz, chlorite, muscovite

QuartzQuartz

ChloriteChlorite MuscoviteMuscovite

High-grade metamorphism• 15 km below the surface to the point melting (when melting occurs)

• Temperatures greater than 400oC

• Common high-grade minerals•garnet, kyanite, sillimanite

GarnetGarnet kyanite sillimanitesillimanite

How do fluids enhance metamorphism?• minerals dissolve – re-precipitated in the rock

• fluids speed up chemical reactions – reduces mineral melting points creating “migmatites”

MigmatiteMigmatite

Melting occurs from loweredmelting points creating small pockets of igneous rocks surrounded by metamorphic rocks

Igneous rock materialIgneous rock material

Metamorphic rockMetamorphic rock

When does metamorphism take place?When does metamorphism take place?

• solid rock coming in contact with hotsolid rock coming in contact with hot magmamagma

• solid rock contacts hot fluids (hot solid rock contacts hot fluids (hot water)water)

• during episodes of intense mountainduring episodes of intense mountain buildingbuilding

• along earthquake fault zonesalong earthquake fault zones

I I I I Solid-state transformations Solid-state transformations Solid-state transformations Solid-state transformations

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

1.1.Define metamorphism, and what is meantDefine metamorphism, and what is meant by a “solid-state-transformation” ?by a “solid-state-transformation” ?

2. What conditions below the surface2. What conditions below the surface characterizes the onset of metamorphism?characterizes the onset of metamorphism?3. What conditions distinguishes the differences3. What conditions distinguishes the differences between high-grade and low-grade metamorphism?between high-grade and low-grade metamorphism?

4. What is a migmatite?4. What is a migmatite?

What are the various types of What are the various types of metamorphism processes?metamorphism processes?

• contact metamorphismcontact metamorphism

• hydrothermal metamorphismhydrothermal metamorphism

• regional metamorphismregional metamorphism

• MetasomatismMetasomatism

What is contact metamorphismWhat is contact metamorphism

• Contact metamorphism:Contact metamorphism:

magma “contacts” solid rock –magma “contacts” solid rock – heat is transferred into overlyingheat is transferred into overlying

rocks through rocks through conductionconduction – changing – changing the pre-existing rock it intrudedthe pre-existing rock it intruded

• high heat / low pressurehigh heat / low pressure• localized metamorphismlocalized metamorphism• “ “fast acting” like touching a fast acting” like touching a hot frying panhot frying pan

Country rock (surrounding) is baked by conductionCountry rock (surrounding) is baked by conduction

What is regional metamorphism?What is regional metamorphism?

Regional MetamorphismRegional Metamorphism

pre-existing rock is subjected to intensepre-existing rock is subjected to intensestresses and strains (deformation) usuallystresses and strains (deformation) usuallyfrom the forces of mountain buildingfrom the forces of mountain building

• high heat / high pressurehigh heat / high pressure• very wide spread geographicallyvery wide spread geographically• like experiencing a slow sun burnlike experiencing a slow sun burn

Mountain building Mountain building

Wide spread beltsWide spread belts

What is hydrothermal metamorphismWhat is hydrothermal metamorphism

Hydrothermal metamorphismHydrothermal metamorphism

the chemical alteration of pre-existingthe chemical alteration of pre-existingrock from the action of hot water –rock from the action of hot water –usually hot water from a magma sourceusually hot water from a magma sourcethat is that is ionion rich rich

• low pressures / high heatlow pressures / high heat• hot water alterationhot water alteration

Black smokersBlack smokers on the ocean floor on the ocean floorhydrothermal alteration – “spewing” hothydrothermal alteration – “spewing” hotwater concentrated in sulfide metalswater concentrated in sulfide metals

Metasomatism• fluids pass in / out of the rock changing thefluids pass in / out of the rock changing the overall chemical compositionoverall chemical composition

• fluids take away or add chemical compoundsfluids take away or add chemical compounds to the rockto the rock

Chemical alteration from fluids --- moving andChemical alteration from fluids --- moving andout of the rockout of the rock

I I I I all types of metamorphism. all types of metamorphism. all types of metamorphism. all types of metamorphism.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

1.1.Briefly describe the conditions for theBriefly describe the conditions for the following types of metamorphisms:following types of metamorphisms:

• contact metamorphismcontact metamorphism• regional metamorphismregional metamorphism• hydrothermal metamorphismhydrothermal metamorphism• metasomatismmetasomatism

What does each metamorphic processWhat does each metamorphic processhave in common?have in common?

Heat:Heat: provides the energy to cause provides the energy to cause recrystallization of pre-existingrecrystallization of pre-existing minerals into “new” type of mineralsminerals into “new” type of minerals

Heat sources:Heat sources:contact with hot magma – heat penetratescontact with hot magma – heat penetrates

overlying rocks (conduction)overlying rocks (conduction)

geothermal gradient – heat increases withgeothermal gradient – heat increases with depth – rocks are hotter when burieddepth – rocks are hotter when buried

Geothermal GradientGeothermal Gradient

• Temperature increasesTemperature increases as depth increasesas depth increases

• Large thermal gradientLarge thermal gradient at the surfaceat the surface

• gradient decreases gradient decreases after 1000 km depthafter 1000 km depth

Geothermal GradientGeothermal Gradient

• Temperature increasesTemperature increases as depth increasesas depth increases

• Large thermal gradientLarge thermal gradient at the surfaceat the surface

• gradient decreases gradient decreases after 1000 km depthafter 1000 km depth

1000100010001000 2000200020002000 3000300030003000 40004000400040000000

Steep gradientSteep gradientSteep gradientSteep gradient

Pressure –Pressure – increases with depth increases with depthvarious types of pressure rearrangevarious types of pressure rearrangeminerals – compacts or elongatesminerals – compacts or elongates

Confining pressureConfining pressure Differential pressureDifferential pressure

I I I I heat and pressure. heat and pressure. heat and pressure. heat and pressure.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

1.1. Describe the characteristics of the geothermalDescribe the characteristics of the geothermal gradient and it influences metamorphism.gradient and it influences metamorphism.

2. Distinguish the differences between both2. Distinguish the differences between both confining and differential pressure.confining and differential pressure.

3. How does confining and differential pressure3. How does confining and differential pressure influence the orientation of mineral grainsinfluence the orientation of mineral grains found in a metamorphic rock?found in a metamorphic rock?

Chemically active fluidsChemically active fluids• commonly hot water carries ions incommonly hot water carries ions in solution and ppt various solids (metals)solution and ppt various solids (metals)

• hot water dissolves minerals and depositshot water dissolves minerals and deposits minerals to other sites – concentratedminerals to other sites – concentrated

goldgold, , silversilver, other earth metals, other earth metals

GoldGold in Quartz vein in Quartz vein

Native Native CopperCopper (Cu) (Cu)

How does one know how much aHow does one know how much arock has been metamorphosed?rock has been metamorphosed?

• the degree of metamorphism isthe degree of metamorphism is reflected in the rocks reflected in the rocks texturetexture and and compositioncomposition

Regional MetamorphismRegional Metamorphism (HP/HT) – high grade(HP/HT) – high grade• rock exhibits arock exhibits a foliationfoliation texturetexture• rocks show a “preferred” mineralrocks show a “preferred” mineral orientationorientation

• parallel mineral alignmentsparallel mineral alignments

How does one know how much How does one know how much aarock has been rock has been metamorphosed?metamorphosed?

Contact MetamorphismContact Metamorphism (HT / LP) low-grade(HT / LP) low-grade

• rock textures decrease in rock textures decrease in foliated textures – “sub” parallel typefoliated textures – “sub” parallel type texturestextures• rocks composed of one type of rocks composed of one type of mineral mineral (same chemistry)(same chemistry) are called are called non-foliatednon-foliated

How does one know the amount of temperature / pressure the rock has beensubjected?

The Metamorphic facies• the set of metamorphic mineral assemblages that form under various temperature/pressure relationships

• Associated with different plate boundaries• Blueschist / Eclogite facies occur in the high pressure environment --- subduction • Greenschist, amphibolite, granulite facies occur along convergent boundaries

Metamorphic faciesMetamorphic facies – mineral assemblages that – mineral assemblages thatrepresent various P / T relationshipsrepresent various P / T relationships

What plate tectonic settings do What plate tectonic settings do metamorphic rocks form?metamorphic rocks form?

Divergent boundariesDivergent boundaries• hydrothermal metamorphismhydrothermal metamorphism with black smokerswith black smokers

Convergent plate boundaryConvergent plate boundary• metamorphism along platemetamorphism along plate boundaryboundary• regional and contact regional and contact metamorphismmetamorphism

ContactContact

RegionalRegional