Metamorphism is the process by which a pre-existing rock (the protolith) is altered into a new metamorphic rock by heat, pressure, or chemically active fluids, without melting. The type of metamorphism depends on the dominant geological process at play.
Step 1: Understanding the Question:
The question asks for the specific type of metamorphism that transforms limestone (a sedimentary rock) into marble (a metamorphic rock).
Step 2: Detailed Explanation:
Let's analyze the transformation and the types of metamorphism:
The transformation from limestone to marble involves the recrystallization of calcite (\(CaCO_3\)) grains into a coarser, interlocking crystalline texture. This process is driven primarily by an increase in temperature.
Contact metamorphism: This occurs when a body of magma intrudes into cooler surrounding rock. The heat from the magma "bakes" the adjacent rock, causing recrystallization. This is a high-temperature, low-pressure process and is the classic setting for the formation of marble from limestone.
Regional metamorphism: This affects large areas and is associated with mountain building, involving both high temperature and high pressure. While marble can form this way, the simple recrystallization of limestone is most commonly cited as an example of contact metamorphism.
Dynamic metamorphism: This is caused by high shear stress along fault zones, primarily involving mechanical deformation.
Hydrothermal metamorphism: This involves chemical alteration of a rock by hot, ion-rich water.
The primary agent for changing limestone to marble is heat, which is the defining characteristic of contact metamorphism.
Step 3: Final Answer:
The transformation of Limestone into Marble is a classic example of contact metamorphism.