Which one of the following is not an agent of metamorphism?

Metamorphism involves the mineralogical and structural adjustment of rocks in a solid state due to changes in physical and chemical conditions. The primary agents of metamorphism are heat, pressure (including compression or directed pressure), and chemically active fluids [1]. Heat is the most critical agent, providing energy for recrystallization. Pressure, often resulting from tectonic compression or burial, induces changes in rock volume and texture [3]. Chemically active fluids facilitate mineral changes through solution and reaction [4]. While 'solution' is a valid mechanism within the context of chemically active fluids, 'decomposition' is primarily associated with chemical weathering and the breakdown of organic matter or minerals at the Earth's surface [1]. Metamorphism specifically excludes weathering and surface processes, focusing instead on transformations occurring deep within the crust under high temperature and pressure [4].

Sources

1. [1] https://oms.bdu.ac.in/ec/content-bucket/30-31-1039-64-20241224_095748.pdf
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Dynamic Metamorphism > p. 173
3. [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Diastrophism > p. 38
4. [4] https://www.usgs.gov/faqs/what-are-metamorphic-rocks