Final answer:
The polymorph of andalusite at 7 kbars of pressure and 450 degrees Celsius is kyanite, indicating a medium-pressure terrane and metamorphism that occurs typically at greater depths.
Step-by-step explanation:
The polymorph of andalusite at 7 kbars of pressure and 450 degrees Celsius is kyanite. Andalusite, kyanite, and sillimanite are polymorphs with the same chemical composition but different crystal structures, which form under different temperature and pressure conditions.
Rocks containing andalusite typically form in low-pressure terranes, whereas kyanite is indicative of a medium-pressure terrane. Thus, at 7 kbars, which corresponds to a depth of approximately 23 km considering the relationship that 300 MPa converts to 10 km depth, andalusite would have undergone a phase change to become kyanite due to the increase in pressure and temperature.