There are three different types of enchantments we use as a tank. Armor enchantments, weapon enchantments and jewelry enchantments. I will touch on all three below.
Prismatic Defense Enchantment
Increases max Health, max Stamina and max Magicka
The prismatic Defense enchantment is optimal for a tank. We rely on all three resources, Health, Magicka and Stamina. This enchantment gives the largest amount of flat resources. Since we use all three these enchantments are excellent to use. The more total stats we can get, the better our resource management will be.
Runes needed to craft: Kuta + Repora + Hakeijo
Reduces the enemy's physical and spellresistance
As a tank we are not only someone who keeps the angry boss away. We also make sure bosses and mobs are debuffed as much as possible. This enchantment contains a small debuff. It is small, yes, but it is worth something and there is definitely no other useful enchantment to run as a tank.
Runes needed to craft: Kuta + Itade + Deteri
Shield Play Enchantment
Reduces the cost of bash and block
Now these are the real enchantments for tanks. These are the only things in the game that reduce your block cost by a flat amount. Also they are in the very end of the block cost formula, making them very strong. If you want to know more about block cost check out this page. I advise to use this enchantment on all three pieces of jewelry.
Runes needed to craft: Kuta + Itade + Kaderi