EARTH MATERIALS — Name the metamorphism type driven by fluid-driven chemical replacement. Which term describes metamorphism in which gases and liquids permeate bedrock and chemically replace elements in mineral grains?

Introduction / Context:
Metamorphism alters rocks in the solid state under changing temperature, pressure, and fluid conditions. A key subtype involves chemical exchange between external fluids and rock, replacing original components with new ones. Identifying this process is fundamental in petrology and ore-deposit studies.

Given Data / Assumptions:

• Fluids (gases/liquids) infiltrate bedrock.
• Elements in minerals are chemically replaced rather than merely recrystallized.
• We seek the correct metamorphism term describing fluid-driven compositional change.

Concept / Approach:
Metasomatism is the process of chemical alteration of a rock by hydrothermal fluids, leading to addition or removal of components. When extensive, the resulting texture and mineralogy can differ markedly from the protolith. This contrasts with simple thermal recrystallization that preserves bulk composition.

Step-by-Step Solution:
Recognize key phrase: “chemical replacement by permeating fluids.”Match to definition: metasomatic metamorphism = metasomatism + metamorphic conditions.Exclude alternatives that emphasize stress or heat without significant fluid-driven mass transfer.Conclude: the correct term is “Metasomatic metamorphism.”

Verification / Alternative check:
Classic examples include skarn formation at limestone–granite contacts, where Ca–Mg carbonates are replaced by calc-silicate minerals via hydrothermal fluids.

Why Other Options Are Wrong:
Dynamic metamorphism — dominated by high stress and deformation (cataclasis, mylonitization).Thermal metamorphism — heat-driven recrystallization with little chemical exchange.Contact metamorphism — local heating near an intrusion; may include fluids but not necessarily pervasive chemical replacement.Regional metamorphism — broad T–P changes over large areas; fluids may act, but the defining feature here is fluid-driven replacement.

Common Pitfalls:
Assuming all contact metamorphism is metasomatic. While they can overlap, metasomatism specifically requires significant mass transfer and chemical replacement.

Final Answer:
Metasomatic metamorphism