What are metamorphic facies used for?

A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area.

Why is identifying metamorphic minerals useful?

Much as the minerals and textures of sedimentary rocks can be used as windows to see into the environment in which the sediments were deposited on the Earth’s surface, the minerals and textures of metamorphic rocks provide windows through which we view the conditions of pressure, temperature, fluids, and stress that …

What is the concept of metamorphic facies?

In current usage, a metamorphic facies is a set of metamorphic mineral assemblages, repeatedly associated in space and time, such that there is a constant and therefore predictable relation between mineral composition and chemical composition. The facies concept is more or less observation-based.

How we use index minerals and metamorphic facies to learn the geologic history of a region?

Geologists use index minerals that form at certain temperatures and pressures to identify metamorphic grade. These index minerals also provide important clues to a rock’s sedimentary protolith and the metamorphic conditions that created it.

What two variables are used to define metamorphic facies?

One of the two variables, temperature and pressure, is very high and the other moderate to very high. The presence of water is important in the genesis of these rocks, since rocks that are originally anhydrous may recrystallize in these facies at lower temperatures and pressures than are otherwise required.

What is amphibolite facies in geology?

amphibolite facies, one of the major divisions of the mineral-facies classification of metamorphic rocks, the rocks of which formed under conditions of moderate to high temperatures (500° C, or about 950° F, maximum) and pressures. Water is usually lost from the parent rock as these changes take place.

What are important minerals found in metamorphic rocks?

These minerals are known as index minerals. Examples include sillimanite, kyanite, staurolite, andalusite, and some garnet. Other minerals, such as olivines, pyroxenes, hornblende, micas, feldspars, and quartz, may be found in metamorphic rocks, but are not necessarily the result of the process of metamorphism.

How are metamorphic rocks used in everyday life?

Quartzite and marble are the most commonly used metamorphic rocks. They are frequently chosen for building materials and artwork. Marble is used for statues and decorative items like vases (Figure 4.15). Ground up marble is also a component of toothpaste, plastics, and paper.

What rock characteristics do geologists use to identify metamorphic facies?

Metamorphic facies are groups of metamorphic rocks that form under the same range of pressure and temperature conditions, but from different parent rocks. Geologists use index minerals such as chlorite, garnet, andalusite, and sillimanite to identify metamorphic zones.

What is an index mineral and why are they important to the study and interpretation of metamorphic rocks?

When an index mineral is found in a metamorphosed rock, it indicates the minimum pressure and temperature the protolith must have achieved in order for that mineral to form. The higher the pressure and temperature in which the rock formed, the higher the grade of the rock.

How do you identify metamorphic facies?

Geologists determine a facies in the lab after examining many specimens under the microscope and doing bulk chemistry analyses. Metamorphic facies is not obvious in a given field specimen. To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition.

What metamorphic facies is Quartzite?

Quartzite is a nonfoliated metamorphic rock composed almost entirely of quartz. It forms when a quartz-rich sandstone is altered by the heat, pressure, and chemical activity of metamorphism.

The concept of metamorphic facies is a systematic way to look at the mineral assemblages in rocks and determine a potential range of pressure and temperature (P/T) conditions that were present when they formed.

What are the characteristic mineral assemblages of metamorphic rocks?

Characteristic mineral assemblages are: The amphibolite facies is a facies of medium pressure and average to high temperature. It is named after amphiboles that form under such circumstances. It has the following mineral assemblages: The granulite facies is the highest grade of metamorphism at medium pressure.

Do mineral assemblages of contact meta- morphism differ at higher pressure?

Mineral assemblages in mafic rocks of the facies of contact meta- morphism do not differ substantially from that of the corresponding regional facies at higher pressure. 2 It is convenient to consider metamorphic facies in

Why are index minerals important in metamorphic zones?

Because index minerals can have overlapping stability conditions, a lower-intensity index mineral can still be present in a higher-intensity metamorphic zone. Knowledge of metamorphic zones makes it possible to draw conclusions about the geological conditions in which metamorphic rocks formed.