In general, if a body of mantle (source) rock is subjected to partial melting, the magma that is produced is expected to be

Basaltic magma

Explanation:

Basaltic magma refers to those magma that are originated from the deeper asthenosphere layer which is located at a depth of approximately 70 to 80 km. These magma are responsible for the formation of oceanic crust.

These are formed when the temperature of the mantle exceeds its melting point, which mainly occurs due to the increasing heat and decreasing amount of pressure and also changes that occurs in terms of its composition.

This type of magma are highly comprised of magnesium, calcium and iron, and have relatively lesser concentration of sodium and potassium.

Thus, when a body of mantle rock undergoes partial melting, then basaltic magma is produced.