Chaos Rift has been cast on 2 of my cities. I tried Disenchant Area and with the bonus mana set to the max of 200 MP. I can never get rid of it.

I wonder the same thing.

Disenchant Area seems to be the primary way to get rid of Chaos Rift, although if you have Life spells Consecration is probably the most effective way.

You have to cast the Disenchant repeatedly to see success. I remember having been frustrated by the mechanism and I thought it was broken. It is not. The disenchant spells are less effective than the spells being dispelled (good concept, try to think about it).

So, you need repeated casting. Reloading does NOT help. Also, the most effective way is not to cast maximum (as you did). This will bring you the quickest success, but for huge mana price. I made a mathematical analysis of it on lost Dragonsword forums. IIRC I suggested using about 30-50% cost of dispelled spell's mana cost. This give you good punch for average mana. Still, you should expect to spend about 200% mana on average before the spell is dispelled. It's costly to destroy a spell.

That's why Disenchant True is so important asset, much more effective. Consecration is not a bad idea either.

There is a life spell consecration you cast on your city which will get rid of and protect one hundred percent against any chaos or death spells including meteor storm and chaos rift..
Also disenchant magic true (sorcery) has a good chance of dispelling any spell against your city and in battle as well.
As well with sorcery you can get a spell (spell ward) which you can choose to stop any spell directed against your city.
Otherwise just keep trying with Disenchant area.
I found it more efficient to cast it at about 2/3s maximum magic power,but I never kept track, that was just my impression.

I always cast the disenchant spells at the base cost, no added mana. Being able to cast 2 base spells is cheaper and a faster way to dispel something than adding mana, which still doesn't guarantee success.

Is it even possible, or feasible, to take down a high-level enchantment fielded by a Chaos Master?

Just wondering if a regular schmuck throwing a Disenchant Area is going to break through THAT spell resistance (Elemental Masters have resistance to dispel magic).

It's late but disenchant with a minor spell cost(IE add 50 over and over or you might get lucky right away),Consecration will take it down,if you have life,once you have it down if you can get the sorcery ward spell you can make it never happen again during that game.