The old archive feature was removed.. Apple decided you no longer need it.
But TM in the Mountain Lion can backup to two different locations.. you can use a USB disk plugged occasionally into the computer and backup to that. (This was always possible by changing target for backup but ML has automated it somewhat).
Or you can manually copy the sparsebundle..
See Q18 http://pondini.org/TM/FAQ.html
He (the grand master pondini) covers most of the possible scenarios..