What is the metamorphic field gradient useful for?

Asked by: Jude Clausen

What is a metamorphic field gradient?

A metamorphic field gradient (MFG) is defined by the array of maximum temperature conditions preserved by a series of exposed rocks which underwent a common orogenic evolution.

What is geothermal gradient in geology?

The geothermal gradient is defined as the increase in temperature with depth in the Earth. In normal continental crust a typical geothermal gradient within the first 3 to 5 kilometers (2 or 3 miles) of Earth’s surface is about 25°C/km.

What is metamorphism time?

Time. Most metamorphic reactions take place at very slow rates. For example, the growth of new minerals within a rock during metamorphism has been estimated to be about 1 mm per million years. For this reason, it is very difficult to study metamorphic processes in a lab.

What is ACF diagram?

ACF diagram A three-component, triangular graph used to show how metamorphic mineral assemblages vary as a function of rock composition within one metamorphic facies. Besides SiO ₂, the five most abundant oxides found in metamorphic rocks are Al ₂O ₃, CaO, FeO, MgO, and K ₂O.

What are metamorphic facies and how are they used to decipher geologic history?

A metamorphic facies is a set of mineral assemblages in metamorphic rocks 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 in Figure 1).

Why is geothermal gradient important?

It indicates heat flowing from the Earth’s warm interior to its surface. On average, the temperature increases by about 25°C for every kilometer of depth. This difference in temperatures drives the flow of geothermal energy and allows humans to use this energy for heating and electricity generation.

Why is the geothermal gradient important for generating melts?

For rocks to melt the geothermal gradient (or geotherm) must cross the solidus (blue line). The solidus marks the transition from solid rock to rock that can melt and form pockets of magma. Because of pressure increases the solidus increases in temperature the further down you go.

What is the importance of temperature gradient in the atmosphere?

The difference in temperature causes differences in air pressure between the two spots. This air pressure differential leads to the formation of winds as the atmosphere tries to equalize the air pressure. Generally, the larger the temperature difference, the stronger the resulting winds will be.

What is the most efficient agent of metamorphism?

Heat is the most efficient agent of metamorphism because it provides the energy to drive reactions.

What are the 2 main factors causing the metamorphism of rocks?

Temperature and pressure. Temperature and pressure are important factors in determining the new minerals that form in a metamorphic rock. Different minerals form under different pressure and temperature conditions.

What controls the metamorphic process?

The main factors that control metamorphic processes are:



The temperature at which metamorphism takes place. The amount and type (direction) of pressure during metamorphism. The amount and type of fluid (mostly water) that is present during metamorphism. The amount of time available for metamorphism.

What does the nature of metamorphic facies depend on?

This pressure and temperature environment is referred to as Metamorphic Facies. The sequence of metamorphic facies observed in any metamorphic terrain, depends on the geothermal gradient that was present during metamorphism.

How do metamorphic facies series relate to geothermal gradient?

The low-P/T type metamorphic facies series occurs in an arc where the geothermal gradient is high, resulting in the progressive change from greenschist facies through amphibolite to granulite facies metamorphic grade as shown in Fig.

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 does the metamorphic grade of a rock tell you?

Metamorphic grade is the degree to which pressure and temperature have altered parent rock. Rocks start as a protolith and progress up from low grade to high grade. Foliated metamorphic rocks increase metamorphic grade from slate→phyllite→schist→gneiss. 2.

What does high and low metamorphic grade mean?

Metamorphic grade refers to the range of metamorphic change a rock undergoes, progressing from low (little metamorphic change) grade to high (significant metamorphic change) grade. Low-grade metamorphism begins at temperatures and pressures just above sedimentary rock conditions.

What can be used to define metamorphic intensity?

The intensity or rank of metamorphism, measured by the amount or degree of difference between the original parent rock and the metamorphic rock. It indicates in a general way the pressure-temperature environment or facies in which the metamorphism took place.

What is metamorphic grade quizlet?

Metamorphic grade is the degree to which a rock has undergone metamorphic change or how much a metamorphic rock differs from the parent rock. It is determined by the increase in pressure and temperature that the parent rock has undergone.

What does a metamorphic grade refer to and how can it be determined?

(Metamorphic grades refer to the degree and intensity of the metamorphism: they are determined by the pressure and temperatures to which the rock has been subjected.) Such areas are generally referred to as metamorphic core complexes.

What is the most efficient agent of metamorphism?

Heat is the most efficient agent of metamorphism because it provides the energy to drive reactions.