Science Olympiad Dynamic Planet Practice Test

What rock does the basalt of the oceanic crust transform into at subduction depths of 80-120 kilometers?

1. Granite

2. Eclogite

3. Pumice

4. Gabbro

The correct answer is: Eclogite

The basalt of the oceanic crust undergoes significant metamorphic processes under high pressures and temperatures at subduction depths of 80-120 kilometers. At these depths, basalt, which is a volcanic rock primarily composed of plagioclase and pyroxene, is subjected to conditions that facilitate transformation into eclogite. Eclogite is a high-pressure metamorphic rock that typically contains the minerals omphacite (a type of pyroxene) and garnet. The formation of eclogite occurs due to the increasing pressure and temperature conditions associated with the subduction of oceanic crust into the mantle. This metamorphic process involves the breakdown of basaltic minerals and the recombination of elements under extreme conditions, leading to the emergence of eclogite with distinct mineral compositions suited for such environments. In contrast, granite is an intrusive igneous rock that forms under different conditions, and it is not a product of the subduction-related metamorphism of basalt. Pumice is a volcanic rock that forms from explosive eruptions and is not related to the metamorphic processes occurring at significant depths in subduction zones. Gabbro, while similar in composition to basalt, is also an intrusive igneous rock and