We develop a theory of minors for alternating dimaps - orientably embedded digraphs where, at each vertex, the incident edges (taken in the order given by the embedding) are directed alternately into, and out of, the vertex. We show that they are related by the triality relation of Tutte. They do not commute in general, though do in many circumstances, and we characterize the situations where they do. We give a characterization of alternating dimaps of at most a given genus, using a finite set of excluded minors. We also use the minor operations to define simple Tutte invariants for alternating dimaps and characterize them. We establish a connection with the Tutte polynomial, and pose the problem of characterizing universal Tutte-like invariants for alternating dimaps based on these minor operations.