Where a user has answered a question, I propose that either
that user cannot vote to close the question
the user's close vote ability is suspended on that question for one week
Conversely, a user who answers a question should be banned or delayed from casting a close vote on that question. Any earlier close vote on that question from that user should be automatically cancelled when they post the answer.
Ability to comment, request closing of the question in meta threads, and to do anything except add a close vote would not be affected. Logically the same request applies to delete votes, but if there are subtle problems with applying it to both I am primarily talking about close votes.
There are several reasons one might want this enforced as a feature [see first revision, or some of the comments here], but I am also posting this question to invite discussion of what "social norms" might exist about the use of the close and delete votes in parallel with answers.