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.
Consequently, what is meant by metamorphic grade?
As the temperature and/or pressure increases on a body of rock we say the rock undergoes prograde metamorphism or that the grade of metamorphism increases. Metamorphic grade is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form.
What is the texture of metamorphic rocks?
TEXTURES Textures of metamorphic rocks fall into two broad groups, FOLIATED and NON-FOLIATED. Foliation is produced in a rock by the parallel alignment of platy minerals (e.g., muscovite, biotite, chlorite), needle-like minerals (e.g., hornblende), or tabular minerals (e.g., feldspars).
What is a metamorphic zone?
In geology, a metamorphic zone is an area where, as a result of metamorphism, the same combination of minerals occur in the bedrock. These zones occur because most metamorphic minerals are only stable in certain intervals of temperature and pressure.
What are the different metamorphic facies?
A metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram at right).
What makes Blueschist blue?
The blue color of the rock comes from the presence of the predominant minerals glaucophane and lawsonite. Blueschists are typically found within orogenic belts as terranes of lithology in faulted contact with greenschist or rarely eclogite facies rocks.
What is subduction zone metamorphism?
A subduction zone is a region of the earth’s crust where one tectonic plate moves under another tectonic plate; oceanic crust gets recycled back into the mantle and continental crust gets created by the formation of arc magmas.
What is mineral assemblage?
The mineral assemblages that occur in metamorphic rocks depend on four factors: The bulk chemical composition of the original rock. The pressure reached during metamorphism. The temperature reached during metamorphism. The composition of any fluid phase that was present during metamorphism.
What is the index minerals?
An index mineral is used in geology to determine the degree of metamorphism a rock has experienced. Depending on the original composition of and the pressure and temperature experienced by the protolith (parent rock), chemical reactions between minerals in the solid state produce new minerals.
What is the grade of metamorphism?
Metamorphic Grade is a scale of metamorphic intensity which uses indicator minerals as geothermometers and geobarometers. SLATE -> PHYLITE -> SCHIST is a sequence of metamorphic rocks of increasing grade. The corresponding indicator minerals are chlorite, biotite and garnet.
What is a sedimentary facies?
Sedimentary facies are bodies of sediment that are recognizably distinct from adjacent sediments that resulted from different depositional environments. Generally, geologists distinguish facies by the aspect of the rock or sediment being studied.
What is an index mineral in metamorphic rock?
Common minerals in metamorphic rocks include quartz, feldspar, mica, calcite, and hornblende. Index minerals in metamorphic rocks indicate how much the original rock was metamorphosed, called the grade of metamorphism. Index Minerals minerals include chlorite, epidote, garnet, staurolite, kyanite and sillimanite.
What is Metasomatism in geology?
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.
What is the parent rock?
Parent rock, also referred to as substratum, refers to the original rock from which something else was formed. It is mainly used in the context of soil formation where the parent rock (or parent material) normally has a large influence on the nature of the resulting soil.
What is the Protolith of a marble?
Protolith (Parent Rock) – A rock which undergoes metamorphism, resulting in formation of a new metamorphic rock. Example: The protolith of the metamorphic rock marble is the sedimentary rock limestone. The protolith of the metamorphic rock quartzite is the sedimentary rock sandstone.
What are the chief types of metamorphic rocks?
There are two basic types of metamorphic rocks. Foliated metamorphic rocks such as gneiss, phyllite, schist, and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure.
What are the three most important agents of metamorphism?
The three agents of metamorphism are heat, pressure, and chemically active fluids. Heat is the most important agent of metamorphism because it provides the energy that drives the chemical reactions responsible for mineral and textural changes during metamorphism.
What are the three different types of metamorphism?
There are three ways that metamorphic rocks can form. The three types of metamorphism are Contact, Regional, and Dynamic metamorphism. Contact Metamorphism occurs when magma comes in contact with an already existing body of rock.
What is the most important agent of metamorphism and why?
Heat as a Metamorphic Agent – The most important agent of metamorphism is heat because it provides the energy to drive the chemical changes that result in the recrystallization of minerals.
What are the different types of metamorphism?
There are two major kinds of metamorphism: regional and contact. Regional metamorphism. Most metamorphic rocks are the result of regional metamorphism (also called dynamothermal metamorphism). These rocks were typically exposed to tectonic forces and associated high pressures and temperatures.
How do you classify metamorphic rocks?
As with igneous and sedimentary rocks, metamorphic rocks are classified on the basis of texture (grain size, shape, orientation) and mineral composition. However, the classifiction of metamorphic rocks is more difficult to get into than with igneous and sedimentary rocks, for a couple of reasons.
Why do the minerals in metamorphic rocks often rearrange in layers?
Great masses of rock are exposed to pressure from rock and sediment layers on top of it. The rock may also be compressed by other geological processes. If the rock is buried deeply, it may experience high temperatures. (A) Regional metamorphic rocks often display layering called foliation.
Is a diamond a metamorphic rock?
Metamorphic Rocks. This is because the minerals that make up the rocks form only at certain temperatures and pressures. At high temperatures or pressures, the elements will rearrange their crystal structure to form a different mineral. Graphite and diamond are two minerals that are both made entirely out of carbon.
Which is the highest grade metamorphic rock?
Schist, the next higher grade rock, typically contains easily visible crystals of muscovite or biotite. Gneiss, the highest grade metamorphic rock, contains bands of easily visible quartz, feldspar, and/or mica. More metamorphic rocks.