There are of course the cot-caught and father-bother mergers, but I was wondering if there are any others that have been identified. In a song I was listening to a few weeks ago, a Philadelphia AAVE speaker rhymes 'caught' and 'depart' (I know it's a bad source, but that's all I have). His realisation for LOT is very fronted, somewhere around [a], while 'depart' and 'caught were both something like [Q@]. I was wondering if there's such a thing as a start-thought merger?
Other low-back mergers
Do you mean rhymes 'caught' and 'depart' non-rhotically? Would 'part' and 'port' be homophones in this merger?