Slab of sorts, asphalt?

Hey guys, I was digging up the yard the other day and found a piece of asphalt under the soil.

Must have been buried there or at least 10-20 years, covered in roots. It’s still solid or at least it didn’t break under a hammer.

I’m thinking of trying to use it as a slab but not sure if it would be safe for the tree.

Any thoughts?