What is metasomatism?
The chemical alteration of rocks by fluids (H₂O and CO₂) that causes a change in the rock’s composition and mineralogy
Derived from the Greek word meta: ‘change’ and soma: ‘body’. This process occurs while the rock remains in a solid state.
Name the types of metasomatic processes based on transport mechanism.
- Diffusional
- Infiltrational
Diffusional involves diffusion of a solute through a stagnant fluid, while infiltrational refers to the transfer of material in solution through the host rock.
What is hydrothermal alteration?
The action of H₂O in altering rocks
Hydrothermal fluids are hot water, steam, and volcanic gases in motion within fractured rocks, influenced by heat from magma.
What is autometasomatism?
Alteration of a recently crystallized igneous rock by its own last water-rich liquid fraction
This generally occurs by an impermeable chilled border.
What is contact metasomatism?
Alteration of rocks due to interaction with hot, fluid-rich magmas or their emanations
This process changes the chemical composition of the rocks.
Define bimetasomatism.
Occurs through two-way diffusion of different chemical elements between rocks
Characterized by the formation of reaction zones where mineral compositions change due to chemical exchange.
What is sericitization?
Feldspars altered to sericite (fine muscovite)
This is a specific type of metasomatic alteration.
What is albitization?
Replacement by albite (Na-plagioclase)
This process alters the mineral composition of rocks.
What is the geological importance of metasomatism?
- Forms ore deposits (Cu, Fe, W, Sn, Au, U)
- Explains chemical zoning around plutons
- Helps in reconstructing fluid pathways and tectonic–magmatic processes
These aspects are crucial for understanding geological formations and resource distribution.
Where is greisenization commonly found?
In granitic rocks altered by hydrothermal fluids
Results in the formation of greisen, characterized by quartz, mica, and topaz.
What is skarn formation?
Metasomatism of carbonates near igneous intrusions
This process leads to the formation of minerals such as garnet, pyroxene, and wollastonite.
What does carbonatization involve?
Addition of CO₂ leading to calcite and dolomite formation
This process can be observed in various geological settings.
What is chloritization?
Ferromagnesian minerals altered to chlorite
This alteration is commonly observed in metabasalt.
Name the types of metasomatism based on rock types.
- Silicification
- Near vein metasomatism
- Regional metasomatism
Silicification involves the addition of SiO₂, while regional metasomatism refers to alteration over a large area.
What is metasomatism?
The chemical alteration of rocks by fluids (H₂O and CO₂) that causes a change in the rock’s composition and mineralogy
Derived from the Greek word meta: ‘change’ and soma: ‘body’. This process occurs while the rock remains in a solid state.
Name the types of metasomatic processes based on transport mechanism.
- Diffusional
- Infiltrational
Diffusional involves diffusion of a solute through a stagnant fluid, while infiltrational refers to the transfer of material in solution through the host rock.
What is hydrothermal alteration?
The action of H₂O in altering rocks
Hydrothermal fluids are hot water, steam, and volcanic gases in motion within fractured rocks, influenced by heat from magma.
What is autometasomatism?
Alteration of a recently crystallized igneous rock by its own last water-rich liquid fraction
This generally occurs by an impermeable chilled border.
What is contact metasomatism?
Alteration of rocks due to interaction with hot, fluid-rich magmas or their emanations
This process changes the chemical composition of the rocks.
Define bimetasomatism.
Occurs through two-way diffusion of different chemical elements between rocks
Characterized by the formation of reaction zones where mineral compositions change due to chemical exchange.
What is sericitization?
Feldspars altered to sericite (fine muscovite)
This is a specific type of metasomatic alteration.
What is albitization?
Replacement by albite (Na-plagioclase)
This process alters the mineral composition of rocks.
What is the geological importance of metasomatism?
- Forms ore deposits (Cu, Fe, W, Sn, Au, U)
- Explains chemical zoning around plutons
- Helps in reconstructing fluid pathways and tectonic–magmatic processes
These aspects are crucial for understanding geological formations and resource distribution.
Where is greisenization commonly found?
In granitic rocks altered by hydrothermal fluids
Results in the formation of greisen, characterized by quartz, mica, and topaz.
