Volcanic rock found on island arcs is most likely to be composed of which substance?

Volcanic rock found on island arcs is primarily composed of basalt. This is because island arcs are typically formed at convergent plate boundaries, where an oceanic plate subducts beneath another oceanic plate. The resulting magma generated in these subduction zones is usually basaltic in composition due to the melting of the mantle and the addition of water from the subducting oceanic plate.

Basalt is a mafic rock, characterized by its relatively low silica content and higher amounts of iron and magnesium, which are common in the melting processes associated with subduction zones. It often forms from the rapid cooling of lava flows, resulting in a dense, dark rock that is predominant in volcanic islands such as those found in the Pacific Ocean.

In contrast, granite is a felsic rock that forms from the slow crystallization of magma beneath the Earth's surface, making it less common in volcanic environments like island arcs. Obsidian is a glassy volcanic rock that can form from the rapid cooling of lava but is not as commonly associated with the bulk of volcanic activity in island arcs. Pumice, while also a volcanic rock, is formed from explosive eruptions and contains gas bubbles, making it less abundant in these specific geological settings. Therefore, basalt is