What is mantle metasomatism?

A geological process involving the alteration of the Earth's mantle by introducing new chemical components.

Which elements commonly migrate during metasomatism?

Heavy metals only found in the lithosphere.

What happens to mantle peridotite when it contacts CO2-rich fluids?

It decomposes into smaller mineral fragments.

What new minerals can form through mantle metasomatism?

Aluminous minerals like garnet and mica, and hydrous minerals.

What geological phenomena is the mantle wedge associated with?

Direct creation of continental crust.

Mantle Metasomatism: Definition & Process

mantle metasomatism

Mantle metasomatism is a geological process where the Earth's mantle undergoes chemical alteration due to the infiltration of fluids or melts, enriching it with elements like potassium, sodium, and trace minerals. This process significantly influences the composition of mantle-derived magmas and impacts the development of mineral deposits and volcanic activity. Understanding mantle metasomatism is crucial for interpreting geotectonic phenomena and natural resource distribution.

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Mantle Metasomatism Definition

Mantle metasomatism is a geological process that involves the alteration of the Earth's mantle due to the introduction of new chemical components. When these components infiltrate the mantle, they change its chemical and mineral composition, leading to significant geological transformations.

The Impact and Process of Mantle Metasomatism

Metasomatism occurs when fluids or melts, often rich in volatile elements, migrate through the mantle's rocks. These components can come from:

Subducting oceanic plates introducing seawater and sediments.
Magma from deeper in the Earth’s mantle.

As these elements and compounds interact with the surrounding rocks, they replace some of the original minerals, creating new ones and altering the mantle's geochemistry.

An essential concept is the partial melting point, which refers to the temperature at which some parts of a rock begin to melt. This is crucial in mantle metasomatism as it affects the extent and type of magma generated.

When mantle peridotite, a rock made mostly of olivine, comes into contact with carbon dioxide-rich fluids, it can transform into carbonatite. This is a new type of rock, demonstrating how metasomatism creates diverse mineral compositions.

Knowing the original mineral composition of mantle rocks helps geologists trace the history of metasomatic processes.

Process of Mantle Metasomatism

Understanding the process of mantle metasomatism is key to studying the Earth's interior and the formation of various geological structures. This process significantly alters the composition and properties of mantle rocks, which plays an essential role in volcanic and tectonic activities.

Chemical Alteration in the Mantle

The process begins when fluids or melts, enriched with different elements, permeate the mantle. This occurs frequently in regions where tectonic plates converge, such as subduction zones. Here, water and other elements from the oceanic crust infiltrate the mantle, instigating metasomatic reactions. Some key points include:

Water drastically lowers the melting point of mantle rocks, aiding the creation of magma.
New minerals form as original minerals dissolve or restructure.

Let's explore the formation of potassium-rich metasomatites. When potassium-bearing fluids penetrate the mantle, they can stabilize new minerals like phlogopite and amphibole, which aren't typically present. These adaptations can inform us about past geochemical processes, indicating rich histories of fluid interaction and tectonic movement.

Consider a scenario where mantle peridotite interacts with silica-rich fluids. This can lead to the formation of pyroxene minerals. These changes illustrate the replacement process characteristic of mantle metasomatism.

Mantle metasomatism can explain the presence of exotic deposits like diamonds, formed deep in the Earth and brought to the surface through volcanic eruptions.

Effects of Mantle Metasomatism

Mantle metasomatism significantly influences the mineral composition and physical properties of the Earth's mantle, impacting various geological processes. By transforming the chemical makeup of mantle rocks, this process can drive changes that shape the Earth's surface and tectonic activity.

Formation of New Minerals and Rocks

The introduction of foreign elements into the mantle through metasomatism leads to the formation of new minerals. This occurs as original minerals dissolve or transform to accommodate the new chemical components. Important changes include:

The development of aluminous minerals like garnet and mica.
Creation of hydrous minerals, which are crucial for magma formation.

A notable example of metasomatism's effects is the creation of eclogite, which consists predominantly of garnet and omphacitic pyroxene. This transformation illustrates how high-pressure conditions can alter basaltic protoliths during metasomatism.

The presence of metasomatic minerals in volcanic rocks can provide clues to the mantle source and history of magmas.

Deep diving into the effects of mantle metasomatism reveals its role in diamond formation. Mantle metasomatism can introduce carbon and other critical elements, facilitating the creation of diamond-stabilizing minerals and conditions. Such insights are unravelling the mysteries of high-pressure environments and mineral resource deposits.

Mantle Wedge Metasomatism

The mantle wedge is a critical site where mantle metasomatism can lead to fascinating geological phenomena. Lying above a subducting tectonic plate, the wedge plays host to processes that alter both chemical and physical properties of mantle rocks.

Mantle Metasomatism and Alkaline Magmatism

Mantle metasomatism has a profound relationship with alkaline magmatism. When mantle rocks undergo metasomatism, they are enriched with volatile components, which can decrease the melting point, leading to the generation of alkaline magma. This magma is notable for its richness in alkali metals like sodium and potassium, exhibiting distinct characteristics:

A classic example of alkaline magmatism influenced by mantle metasomatism is the formation of nepheline syenite and phonolite volcanic rocks. These rocks are indicative of a mantle source that has undergone extensive metasomatic processes.

Delving deeper, mantle metasomatism may lead to the development of rare earth element (REE) enriched magmas. As metasomatic fluids impart elements such as zirconium, niobium, and tantalum into the mantle, the resulting magmas are not only alkaline but also possess high concentrations of these economically valuable elements. Understanding these processes can have implications for mineral exploration and extraction.

Alkaline magmas often erupt in tectonic settings such as rift zones and within continental interiors, where mantle metasomatism plays a pivotal role.

Metasomatized Mantle Characteristics

Characteristics of a metasomatized mantle distinctively include the development of new mineral assemblages and changes in physical properties. Some identifiable features of metasomatized mantle rocks encompass:

For instance, the presence of phlogopite mica and amphibole within mantle peridotites becomes a hallmark of metasomatism. These hydrous minerals indicate previous fluid activity altering the mantle's original mineral composition.

Mineralogical changes: Introduction of hydrous minerals such as amphibole and phlogopite.
Geochemical signals: Enrichment of incompatible elements like chlorine, fluorine, and light rare earth elements.

The alteration also affects the mantle's density and seismic velocity, often making it more buoyant and less rigid. It provides clues to mantle dynamics and aids in understanding plate tectonics and volcanic activity.

mantle metasomatism - Key takeaways

Mantle metasomatism definition: A geological process involving the alteration of Earth's mantle by the introduction of new chemical components, changing its chemical and mineral composition.
Process of mantle metasomatism: Involves the migration of fluids or melts through mantle rocks, leading to changes in mineral and chemical composition, often occurring in subduction zones.
Mantle wedge metasomatism: Occurs above subducting tectonic plates, altering the chemical and physical properties of mantle rocks, influencing mantle dynamics.
Effects of mantle metasomatism: Alters mineral composition and properties of mantle rocks, forming new minerals and influencing volcanic and tectonic activities.
Mantle metasomatism and alkaline magmatism: The process enriches mantle rocks with volatiles, lowering melting points and generating alkaline magma rich in alkali metals.
Metasomatized mantle characteristics: Distinguished by new mineral assemblages, such as hydrous minerals like amphibole and phlogopite, and geochemical enrichments, affecting density and seismic velocity.

Frequently Asked Questions about mantle metasomatism

How does mantle metasomatism affect the composition of the Earth's crust?

Mantle metasomatism affects the Earth's crust composition by introducing new elements and minerals from the mantle, altering the chemical and mineralogical makeup. This process can lead to the formation of enriched magmas, which upon crystallization, contribute to crustal growth and diversification in continental crust structures.

What is the role of mantle metasomatism in the formation of igneous rocks?

Mantle metasomatism enriches the mantle with volatile components and trace elements, altering its composition and lowering its melting point. This process leads to partial melting, which generates magma that can ascend to form igneous rocks, influencing their mineral and chemical composition.

What are the mechanisms driving mantle metasomatism?

Mantle metasomatism is driven by the infiltration of fluids or melts that alter the chemical and mineralogical composition of the mantle. These fluids or melts introduce new elements and promote reactions that form new minerals. This process can be triggered by plate tectonics, subduction zones, and mantle plumes.

How does mantle metasomatism influence volcanic activity?

Mantle metasomatism alters the chemical composition of the mantle by introducing volatile-rich fluids or melts, which can lower the melting point and enhance magma generation. This process can increase magma production, potentially leading to more intense or frequent volcanic activity.

How does mantle metasomatism contribute to mineral resource formation?

Mantle metasomatism alters the chemical composition of the mantle by fluid or melt interactions, which can lead to the formation of economically important mineral deposits. This process can enrich the mantle in elements such as gold, copper, and rare earth elements, creating potential mineral resource zones.

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mantle metasomatism

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Mantle Metasomatism Definition

The Impact and Process of Mantle Metasomatism