Why would a plume of solid silicate rock rising slowly from deep in the mantle begin melting as it neared the base of

Question

Question: Why would a plume of solid silicate rock rising slowly from deep in the mantle begin melting as it neared the base of the lithosphere?

Options:

1. The rock heats up and expands at lower pressures, causing it to liquefy.
2. Temperatures remain high as lowered pressures decrease melting temperatures.
3. The lowered pressures cause rapid heat loss accompanied by melting.
4. None of the above

Answer 1

2. Temperatures remain high as lowered pressures decrease melting temperatures.

A plume of solid silicate rock rising slowly from deep in the mantle begin melting as it neared the base of the lithosphere because temperatures remain high as lowered pressures decrease melting temperatures.