The two major prophecies that help ground the dating are the Animal Apocalypse (chs. 85-90) and the Apocalypse of Weeks (chs. 91-93).
Qumran is the site of the Dead Sea Scrolls. It seems to have been a community of apocalyptic Jewish separatists who were in conflict with the Jerusalem establishment over issues of purity, sacrifice, and the calendar. They regarded the Hasmonean (Maccabean) priesthood in particular to be quite corrupt. Scholars disagree whether or not the community was made up of the Essenes mentioned by Josephus and Pliny.
The Similitudes or Parables of Enoch has not been found among the Qumran materials causing speculation about a late date (post-Christian) for this section. Championed by Milik in his edition of the Qumran fragments, this view has not gained widespread support.
John J. Collins, The Apocalyptic Imagination: An Introduction to the Jewish Matrix of Christianity, (New York: Crossroad, 1984), 33-34.
1 Enoch gives us great insight into how the apocalyptic groups at the turn of the era regarded their world-a highly elaborate architecture populated by angelic beings and spirits, both benign and malevolent-and expectations for a messiah and God's initiation of a messianic age.