Does Cavern of Souls trigger when it enters the battlefield and does its naming ability use the stack?
Please autocard: [c]Shard Phoenix[/c] = Shard Phoenix.
Mana abilities don't use the stack and can't be responded to. Even if they did, since you played a land, it's probably your main phase, so your opponent doesn't have priority. He can't activate Tectonic Edge even if he wanted to.