Metamorphic Intensity: Understanding the Transformation of Rocks

What are the rocks listed in order of increasing metamorphic intensity?

1. A metamorphosed mafic rock containing chlorite, epidote, and amphibole

2. A mafic rock metamorphosed at amphibolite facies conditions

3. A metamorphosed pelitic rock containing sillimanite, garnet, feldspar, and quartz

Answer:

The rocks listed in order of increasing metamorphic intensity are as follows:

1. Metamorphosed mafic rock containing chlorite, epidote, and amphibole: This rock has undergone a relatively low degree of metamorphism.
2. Mafic rock metamorphosed at amphibolite facies conditions: This rock has experienced a higher degree of metamorphism compared to the previous rock.
3. Metamorphosed pelitic rock containing sillimanite, garnet, feldspar, and quartz: This rock exhibits the highest level of metamorphic intensity among the listed rocks.

Metamorphism is a fascinating process that transforms rocks under varying pressure and temperature conditions. It brings about changes in mineral composition and structure, leading to the formation of new rocks. Understanding the different levels of metamorphic intensity is key to deciphering the history and conditions under which rocks have undergone transformation.

The first rock in the list, a metamorphosed mafic rock containing chlorite, epidote, and amphibole, indicates a moderate level of metamorphic intensity. This rock likely experienced greenschist facies conditions, which represent a moderate level of metamorphism. The presence of these minerals suggests some recrystallization and reconstitution of the rock's composition.

Moving up the intensity scale, the mafic rock metamorphosed at amphibolite facies conditions signifies a higher degree of metamorphism. This rock endured higher temperatures and pressures, resulting in more significant mineralogical changes. The transformation indicates a more intense metamorphic process compared to the previous rock.

Finally, the metamorphosed pelitic rock containing sillimanite, garnet, feldspar, and quartz showcases the highest level of metamorphic intensity among the listed rocks. This rock has been subjected to high-grade metamorphic conditions, likely in the sillimanite or granulite facies. The presence of these minerals highlights the profound changes that occurred during metamorphism, pointing towards the most intense form of transformation.

By understanding the order of increasing metamorphic intensity in rocks, we gain insights into the geological processes that have shaped the Earth's crust over millions of years. Each rock tells a story of transformation under varying metamorphic conditions, unraveling the intricate tapestry of our planet's history.