Two continental collision zones, Plateau X and Plateau Y, lie at similar elevations and both have thick continental crusts. Plateau X shows widespread volcanic cones, lava fields, and geothermal activity, while Plateau Y shows intense mountain-building but no surface volcanism. Seismic studies confirm the absence of subducting slabs beneath both regions. Which explanation best accounts for volcanism in Plateau X but not in Plateau Y?
Answer
A
The absence of a subducting slab beneath Plateau Y causes magma to cool rapidly, leading to shallow intrusions rather than eruptions.
B
Plateau X may be located above a mantle plume, providing a localized heat source that promotes partial melting despite the absence of subduction.
C
Plateau Y’s mountain-building processes consume crustal material too quickly for magma chambers to form, preventing surface volcanism.
D
Volcanic activity in Plateau X is likely due to crustal thinning from extensional tectonics common to all continental collisions.
Explanation
A mantle plume can supply concentrated heat that causes mantle rock to partially melt and generate magma, even where no slab is subducting. This explains why Plateau X can have volcanic cones, lava fields, and geothermal activity while Plateau Y does not. The absence of a slab alone does not explain the difference, and extension is not present in all continental collision zones.
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