Geology 101 Chapter 7 UNLV

Foliated rocks include...

slate, phyllite, schist, and gneiss

shock metamorphism

the changes that can occur in a rock due to the passage of a shock wave, generally resulting from a meteorite impact (also lightning)

metamorphic aureole

the distinct belt of metamorphic rock that forms around an igneous intrusion

metamorphic grade

the intensity of metamorphism that formed the rock

isograd

the line on a map along which an index mineral first appears

protolith

the original rock from which a metamorphic rock formed; "parent rock"

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

metamorphism

the process in which one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure

Phase Change

transforms one mineral into another mineral (a polymorph) with the same composition but a different crystal structure. On an atomic scale, _________ involves the rearrangement of atoms.

contact metamorphism

A change in the texture, structure, or chemical composition of a rock due to contact with magma.

stress

A force that acts on rock to change its shape or volume

Greenstone

A low-grade granoblastic rock produced by the metamorphism of mafic volcanic rock and containing abundant chlorite, which accounts for its greenish cast

phyllite

A low-grade, fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica. Has a sheen, unlike slate. Tend to be green.

metaconglomerate

A metamorphic rock produced by metamorphism of a conglomerate; typically, it contains flattened pebbles and cobbles.

migmatite

A rock formed when gneiss is heated high enough so that it begins to partially melt, creating layers, or lenses, of new igneous rock that mix with layers of the older gneiss.

metamorphic facies

A set of metamorphic mineral assemblages indicative of metamorphism under a specific range of pressures and temperatures.

slate

A type of low grade Metamorphic rock that was once shale rock formed by heat and pressure. Most common metamorphic rock. Harder than shale, won't fall apart in water.

metamorphic rock

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.

foliation

An arrangement of minerals in flat or wavy parallel bands.

At what temperatures do metamorphic rocks usually form at?

Between 250 and 850 degrees celsius

What forces create a metamorphic mineral assemblage?

Change in temperature and/or pressure, application of compression or shear, and interaction with hydrothermal fluids

hydrothermal metamorphism

Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock.

Where is bluschist formed?

Deep in the ocean where temperatures are low but pressure is high; in accretionary prisms.

Geologists separate metamorphic rocks into what two groups?

Foliated and nonfoliated rocks

What is migmatite a mixture of?

Igneous and metamorphic rock

What is the difference between low, intermediate, and high grade rocks?

Low grade rocks are formed at low temperatures. High grade rocks are formed at high temperatures. Intermediate rocks are formed at temperatures between low and high.

gneiss

Metamorphic Foliated rock- formed from granite; has dark and light bands, hard, durable

What can be found at mountain ranges?

Metamorphic rocks can be found at mountain ranges

What are the features of metamorphism?

Recrystallization, phase changes, metamorphic reactions, pressure solutions, and/or plastic deformation. If hydrothermal fluids bring in or remove elements, we say that metasomatism has occurred.

hornfels

Rock that undergoes metamorphism simply because of a change in temperature, without being subjected to differential stress.

Low to High Grade Metamorphism Changes (Foliated)

Shale (protolith) > Slate > Phyllite > Schist > Gneiss > Migmatite

Trinitite (also known as atomsite or Alamogordo glass)

The glassy residue left on the desert floor after the plutonium-based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico. The glass is primarily composed of arkosic sand composed of quartz grains and feldspar that was melted by the atomic blast. It is usually a light green, although color can vary. It is mildly radioactive but safe to handle.

An isograd indicates what?

The location at which an index mineral first appears.

preferred orientation

The metamorphic texture that exists where platy grains lie parallel to one another and/or elongate grains align in the same direction.

exhumation

The process (involving uplift and erosion) that returns deeply buried rocks to the surface.

metamorphic zone

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

shield

a broad region of long-lived, stable continental crust where sedimentary "cover" either was not deposited or has been eroded away so that Precambrian "basement" rocks are exposed

quartzite

a metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone; it is extremely durable

Recrystallization

changes the shape and size of grains without changing the identity of the mineral making up the grains

regional metamorphism (tectonic burial)

formation of metamorphic rock bodies that are hundreds of square kilometers in size

Plastic Deformation

happens when a rock becomes warm enough to behave like soft plastic, so the minerals within it can change shape without breaking.

Pressure Solution

happens where the surface of one mineral grain pushes against the surface of another, under conditions that allow a water film to exist between the grains. The grains preferentially dissolve at the surface of contact and the resulting ions migrate away, through the water film. The ions may precipitate on the sides of grains that aren't being pushed together.

Non-Foliated rocks include...

hornfels, quartzite, marble, greenstone, and some mylonite

Geologist track the distributions of different grades of rock by looking for...

index minerals

marble

metamorphic rock that was once limestone; often used for sculptures

schist

metamorphic, foliated, lots of mica, intermediate grade

thermal metamorphism

metamorphism caused by heat conducted into country rock from an igneous intrusion

burial metamorphism

metamorphism due only to the consequences of very deep burial; mostly get low-grade rocks under this

dynamic metamorphism

metamorphism that occurs as a consequence of shearing alone, with no change in temperature or pressure; happens along fault

When you fire up a kiln, a pot recrystallizes and clay turns into...

mica

metamorphic mineral

new minerals that grow in place within a solid rock under metamorphic temperatures and pressures

Metamorphic foliation can be defined by....

preferred mineral orientation (aligned inequant crystals) or by compositional banding

Metamorphic Reaction (Neocrystallization)

results in growth of new minerals that differ from those of the protolith. During _________________, chemical reactions effectively "digest" minerals of the protolith, so the chemicals can go into the production of new minerals.