The "zen circle" is the enso. The enso represents our unconditioned nature, to use the zen phrase, "your face before your parents are born." There's no connection with the chakras. Meditation on the chakras is connected with tantra, both Hindu and Buddhist, and more recently, theosophy. The dharmachakra refers to three cycles of teaching in Buddhism: the first on cause and effect, the second on emptiness, and the third on buddha nature. It has no connection to meditation on the chakras.
Imagine a man who stands before a mirror; a stone strikes it, and it falls to ruin all in an instant. And the man learns that he is himself, and not the mirrored man he had believed himself to be.
-- Gene Wolfe