Yes, there's a chemical component as well. I was simplifying. Regardless, though, they're not core material rising up. They're still basically olivine+pyroxen

Yes, there's a chemical component as well. I was simplifying. Regardless, though, they're not core material rising up. They're still basically olivine+pyroxenes+etc, same as what's around them. They're not the exact same, and indeed they bring deep mantle material up, but they're not nickle-iron rising up from the outer core, which is what I was trying to get across.