  In this paper, we study heterodimensional cycles of two-parameter families of
3-dimensional diffeomorphisms some element of which contains nondegenerate
heterodimensional tangencies of the stable and unstable manifolds of two saddle
points with different indexes, and prove that such diffeomorphisms can be well
approximated by another element which has a quadratic homoclinic tangency
associated to one of these saddle points. Moreover, it is shown that the
tangency unfolds generically with respect to the family. This result together
with some theorem in Viana, we detect strange attractors appeared arbitrarily
close to the original element with the heterodimensional cycle.
