Chapter 7 Metamorphism and Metamorphic Rocks

Isotherm

A line along which the temperature of rock (or other material) is the same.

What is the difference between a foliated and non-foliated metamorphic rock? Why?

Foliated- parallel alignment of textural and structural features of a rock. Platy minerals. (Have layered or banded appearance) Non-foliated- Not layered or banded.

What happens to a rock as metamorphism increases to higher grades?

Higher metamorphic grade = higher temperature lower metamorphic grade = lower temperature.

What does an index mineral indicate? An assemblage?

Index minerals- minerals found in rocks that can help determine pressure and temperature in which it was formed.

What does a P-T-t diagram tell us?

Index/assemblage of minerals can help determine approximate temperature and pressure from where it formed.

How are metamorphic rocks brought to the surface?

Metamorphic rocks rise to the surface because hot magma is less dense.

Metasomatism

Metamorphism coupled with the introduction of ions from an external source.

How does parent rock composition influence metamorphism?

Metamorphism- changes to rock that take place in earths interior. 3 characteristics of parent rock that can change it 1.) pressure 2.) temperature 3.) fluids

What is prograde vs. retrograde metamorphism? How does tectonic boundary influence the P-T path?

Prograde metamorphism- when a rock is buried deeper and deeper it is subjected to higher temperature/pressure. It must recrystallize into a higher grade rock. Retrograde- absence of water = cooler temperature when water is introduced to the rock after peak metamorphism.

Geothermal Gradient

Rate of temperature increase associated with increasing depth beneath the surface or Earth (normally about 25 degrees C per kilometer).

What are major textural classes of metamorphic rock? What determines the textures? What causes these textures?

Salty Cleavage- splits easily along really flat and parallel panels. Schitose- Minerals are platy or needle shape have grown essentially parallel to plane due to differential stress. Gneissic- Rock became ductile and the new minerals separated into distinct layers. The mineral content of the metamorphic rock is controlled by the chemical composition of the parent rocks.

Schistose

The texture of a rock in which visible platy or needle-shaped minerals have grown essentially parallel to each other under the influence of directed pressure.

Metamorphism

The transformation of preexisting rock into texturally or mineralogically distinct new rock as a result of high temperature, high pressure, or both but without the rock melting in the process.

Differential Pressure

When pressures on a body are not of equal strength in all directions.

Pressure

A significant type of mechanical weathering that causes rocks to crack when overburden is removed.

Tensile Stress

A stress due to a force pulling away on a body.

Compressive Stress

A stress due to a force pushing a body together.

Lithostatic Pressure

Confining pressure due to the weight over overlying rock.

Know types of metamorphism (regional, contact, etc.), how is each characterized (high pressure-high temp etc.), where each occurs (type of plate boundary etc.).

Contact metamorphism- (thermal) high temperature, relatively low pressure occurs when a body of magma intrudes cool country rock and "bakes" it. (igneous intrusion) Regional metamorphism- Considerable depth, foliated, differential stress, high temperature and pressure. Usually takes place along mountains ranges. Hydrothermal metamorphism- Rocks that have been precipitated from hot water or have been altered by hot water (mid-ocean ridges). Burial- Transforms sedimentary rocks. High pressure- Along linear belts of volcanic arcs, high pressure, produced continent-cont collision.

Foliation

Parallel alignment of textural and structural features of a rock.