Characteristics of Green Schist Facies

Which of these minerals assemblage is characteristic of a greenschist facies?

1) chlorite, actinolite, epidote, albite
2) Quartz, muscovite, biotite, garnet
3) Calcite, dolomite, gypsum, halite
4) Pyroxene, olivine, plagioclase, orthoclase

Answer:

The mineral assemblage of chlorite, actinolite, epidote, and albite is characteristic of greenschist facies, indicating low to medium grade metamorphism. So, the correct answer is option 1.

Explanation: The mineral assemblage characteristic of a greenschist facies is 1) chlorite, actinolite, epidote, albite. These minerals are indicative of low to medium grade metamorphic conditions typically associated with the greenschist facies. Greenschist facies rocks generally form under conditions of low temperature and moderate pressure and have a greenish color due to the presence of green minerals like chlorite and epidote.

Understanding the mineral assemblages and characteristics of different metamorphic facies is important in determining the conditions under which rocks have undergone metamorphism. By identifying key minerals like chlorite, actinolite, epidote, and albite in greenschist facies rocks, geologists can infer the temperature and pressure conditions that existed during the metamorphic process.

Studying metamorphic facies not only provides insights into the geological history of a region but also helps in interpreting the tectonic processes that have shaped the Earth's crust over time. The presence of specific minerals can reveal details about the pressure-temperature conditions and the type of metamorphism that occurred.

Overall, the mineral assemblages found in different metamorphic facies are a key to unraveling the complex processes that have influenced the formation and evolution of rocks in the Earth's crust. By recognizing the characteristic minerals of greenschist facies, geologists can piece together the puzzle of Earth's geological past.