Petrography

Hornfels...

have less or no foliation, and recrystallized without shear stress.

Marble...

have no foliation, and its protolith is limestone.

Quartzite...

have no foliation, and its protolith is sandstone.

Garnet is...

isotropic.

Usually, metamorphic rocks experience their maximum pressure...

on the prograde path.

Calcite is...

uniaxial (-).

What index mineral indicates the highest grade of metamorphism?

2nd Sillimanite

What does a phase represent in metamorphic reactions?

A certain mineral

An example of a polymorphic phase reaction would be...

Al2SiO5

Mineral paragenesis:

An equilibrium mineral assemblage created by metamorphic reactions.

What scenario would result in a large zone of contact metamorphism?

An intrusion of a granitic pluton 10 km in diameter.

Al2SiO5 polymorphs are...

Andalusite, kyanite, and silimanite.

Hydrothermal metamorphism:

Changes caused by interaction of rocks with hot aqueous fluids.

What index mineral indicates the lowest grade of metamorphism?

Chlorite

What metamorphic zones does the Barrovian Facies contain?

Chlorite, biotite, garnet, staurolite, kyanite, sillimanite, and 2nd sillimanite.

At equilibrium, the mineralogy for metamorphic rocks is determined by T, P, and X. What does X stand for?

Composition

What metamorphic facies does the Barrovian Facies contain?

Green schist, amphibolite, and granulite.

Kyanite is formed under...

High pressure

Sillimanite is formed under...

High temperature

To name metamorphic rocks one must put the ____________ first and then the __________.

Highest mineral grade ... texture

Andalusite is formed under...

Low pressure

As temperature and pressure increases in regional metamorphism, what does not occur?

Major changes in bulk composition.

What metamorphic rock is experienced at the highest temperature?

Migmatite.

What is the lowest grade index mineral in an Amphibolite facies?

Staurolite

Confining pressure:

Stress that is applied uniformly in all directions.

Index minerals:

They form under a relatively restricted range of pressure and temperature.

Retrograde reaction:

When mineral changes take place during a decreasing temperature.

Prograde reaction:

When mineral changes take place during an increasing temperature.

Metamorphic phase diagrams mainly have ________ component diagrams.

3

Amphibolite facies conditions are approximately...

400 Celsius and 15km depth.

Metamorphic foliation:

A fabric defined by parallel surfaces or layers that develop in a rock as a result of metamorphism; schistocity and gneissic layering are examples.

Metamorphic facies:

A family of metamorphic rocks with characteristic minerals formed under specific temperature and pressure conditions.

When does the prograde reaction changes to retrograde?

At maximum temperature

Where can we find hydrothermal metamorphism?

At oceanic ridges.

Why are retrograde reactions rare in metamorphic rocks?

Because the rates of these reactions are dependent on temperature and because the fluids have been expelled from the rocks.

Mylonitic texture:

Crystals undergo grain size reduction due to high strain.

Gneissic texture:

Dark and light-colored minerals segregate into compositional bands.

What process happens before metamorphism?

Diagenesis

Schistosity:

Elongate and platy minerals recrystallize along parallel planes.

The Phase Rule

F = C - P + 2

What textural feature is most associated with regional metamorphism?

Foliation

Differential stress:

Forces that are unequal in different directions.

What is the highest grade index mineral in a Green schist facies?

Garnet

High grade metamorphic rocks would be...

Gneiss and migmatite.

Metamorphism:

Isochemical changes of a rock, usually little or no gain or loss of mass.

Regional metamorphism:

Large scale metamorphism associated with mountain building.

Contact metamorphism:

Local scale metamorphism, due to intrusion of igneous rocks.

How do we figure out the stable phases of a bulk (star) composition in a phase diagram?

Look for the triangle in which the bulk (star) composition is located. The three corners of the triangle would be the stable phases.

Devolatization:

Loss of a volatile phase. Dependent on partial pressure of a volatile.

Which group of minerals is most likely responsible for the strong foliation in a garnet-kyanite schisy?

Muscovite and biotite

Continuous (divariant) net transfer reactions:

Phases change proportions and compositions, but do not suddenly appear or disappear.

Agents of metamorphism include:

Pressure, heat, and chemically active fluids.

Ion exchange reaction:

Reciprocal exchange of components between two or more minerals. Basis for geothermobarometers.

What minerals are remnants of a previous assemblage that are present but are no longer stable?

Relict minerals

What is the most likely protolith of a metamorphic rock with the assemblage... wollastonite-calcite-garnet-epidote?

Sandy limestone.

What is the most likely protolith of a metamorphic rock that now has the assemblage kyanite-staurolite-muscovite-quartz?

Shale.

We do not often include what in metamorphic 3-component diagrams, because its always present?

Silica

What is the highest grade index mineral in an Amphibolite facies?

Sillimanite

Low grade metamorphic rocks would be...

Slate and phyllite.

Slaty cleavage:

Tendency to split along parallel planes.

The pressure and heat that drive metamorphism result from which three forces?

The internal heat of the Earth, the weight of the overlying rocks, and horizontal pressures developed as rocks become deformed.

Zone:

The map area between two isograds, named after the lower of the isograds.

Protolith:

The original rock from which a metamorphic rock formed.

Metasomatism:

The process by which a rock's overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove elements.

Univariant (discontinuous) net transfer reactions:

The process in which 2 phase react to form a third (or more phase) at a single pressure and temperature.

Exsolution:

The process where an initially homogeneous solid solution separates into two (or more) distinct crystalline minerals without the addition or removal of material to or from the system.

Metamorphic zone:

The region between two metamorphic isograds, typically named after an index mineral found within the region. (Index mineral)

Metamorphism:

The solid-state change in composition, mineralogy, or texture of pre-existing rocks due to the change in temperature, pressure or chemical components.

Isograd:

The trace in outcrop of the appearance of a mineral phase.

There is never any garnet in a rock from the biotite zone in Barrovian metamorphism. True/False

True

The reaction kyanite to andalusite is an example of...

a polymorphic phase transition.

Staurolite is...

brown to black in hand sample, and strong golden yellow and shaped like Swiss cheese under the microscope.

What minerals are not likely to be found together in a metamorphic rock?

calcite and wollastonite.

Green schist facies conditions often produce rocks with...

chlorite and quartz.

Amphibolites...

come from hornblende-plagioclase rocks, they contain garnet, and have variable foliation.

The hornfels facies forms during ____________________ metamorphism.

contact

As grade of metamorphism increases...

crystal size and foliation increases.

Strained quartz is indicative of...

deformation.

At equilibrium, the number of components in a rock should...

equal the number of phases.

Protolith rocks for metamorphism are grouped into ______ families.

five

Eclogite facies happens at...

high T, high P

Granulite facies is a _______ metamorphic facies.

high grade

The petrogenetic grid...

is a diagram that links the stability ranges of metamorphic minerals or mineral assemblages to the conditions of metamorphism.

Eclogite...

is a garnet-pyroxene rich rock.

Granulite...

is a very high grade metamorphic rock, that usually comes from granitic rocks.

Protoliths of marble and schist are...

limestone and shale.

Blue schist facies happens at...

low T, high P

Zeolite facies is a __________ metamorphic faceis.

low grade

A polymorphic phase transformation is when...

there is no change in phase compositions, only in crystal structure of a single phase.

The only shape allowed in phase diagrams are...

triangles.