Question

Mafic rocks like basalt and gabbro ________.

A) are major constituents of the continental crust
B) are very low in their iron and magnesium contents
C) form mainly in continental mountain belts
D) make up most of the ocean floor and volcanic island chains

Answer 1

Mafic rocks like basalt and gabbro make up most of the ocean floor and volcanic island chains, differing from the mainly granite composition of the continental crust.

Step-by-step explanation:

Mafic rocks such as basalt and gabbro make up most of the ocean floor and volcanic island chains. These rocks are rich in iron and magnesium, which contrasts with rocks like granite that make up a significant portion of the continental crust. The oceanic crust is largely composed of basalt, which is an igneous rock that forms from the cooling of mafic magma either on the seafloor or as an intrusive rock deeper down like gabbro. Furthermore, these types of rocks are also found in large igneous provinces which are extensive areas of predominantly mafic rock formation beyond normal seafloor spreading.