Here's the text from the Minecraft Wiki (minecraft.gamepedia.com):
" [...] Upon detonation after activating on activator rail, it will not destroy its rails and the blocks the rail is on, however other nearby carts can. [...] "
I tried to detonate a minecart with TNT on an activator rail powered by a redstone torch, but the rail and blocks under are destroyed.
I researched with word "minecart" and "minecart with TNT" before creating this ticket. Sorry if it's duplicate.