Carter (2007) uses the term "metagenre" to designate "broader patterns of language as social action, similar kinds of typified responses to related recurrent situations" (p 393). He does this in the context of a discussion of academic ways of knowing, doing, and writing across the disciplines. "Metagenre" in this sense describes similar ways of knowing, doing, and writing, in related disciplines.
Carter, M. (2007). Ways of Knowing, Doing, and Writing in the Disciplines. College Composition and Communication, 58(3), 385–418.
In a dataset from one land-grant institution Carter (2007) finds four metagenres, that is, academic situations, that call for four kinds of responses: problem-solving, empirical inquiry, research from sources, and performance.
Compare with Giltrow's earlier use of the hyphenated term, meta-genre (2002), which Carter cites in a footnote as a different term.
Ruth Mirtz first used this word to describe student writing: "a kind of experimental, knowledge-building writing which contains many other kinds of writing" (p. 194).
Mirtz, R. (1994). The territorial demands of form and process: The case for student writing as a genre. In W. Bishop & H. Ostrom (Eds.), Genre and writing: Issues, arguments, alternatives. Portsmouth: Boynton/Cook, 190-98.