Final answer:
An isograd represents a line of equal metamorphic intensity or grade that separates different levels of metamorphic rocks based on changes in pressure and temperature. Isograds can be identified by mapping the changes in mineral assemblages or the appearance of new minerals in the rocks at different locations.
Step-by-step explanation:
An isograd represents a line of equal metamorphic intensity or grade. It is a boundary line that separates different levels of metamorphic rocks based on the changes in pressure and temperature that occur during metamorphism.
For example, in the Barrovian sequence of metamorphic rocks, the further away from the collision center or the higher up in the crust the rock is, the lower the grade of metamorphism. As you approach the collision center or go deeper into the crust, the grade of metamorphism increases. The isograds mark these changes in metamorphic grade.
Isograds can be identified by mapping the changes in mineral assemblages or the appearance of new minerals in the rocks at different locations.