Which crust types are involved in forming ocean basins during seafloor spreading?

• A. Sedimentary crust
• B. Only continental crust
• C. Oceanic basalt crust and continental granite crust
• D. Only oceanic crust

Answer: (C)

Seafloor spreading creates new oceanic crust at mid-ocean ridges from upwelling mantle, and this oceanic crust is basalt. At the same time, the nearby continental crust is stretched and thinned as the continents split apart, and that continental crust is granitic. The ocean basin forms as the continental margins separate and the space is filled with newly created oceanic crust. So both types—oceanic basalt crust and continental granite crust—are involved in forming ocean basins during this process. Sedimentary crust isn’t the primary crust type here, and focusing on only one crust would miss the role of the other in creating and bounding the basin.