  The equations that govern the weakly nonlinear near-resonant interaction of a
parent magnetorotational instability with two linearly stable daughter modes in
thin nonuniform magnetized Keplerian discs are derived. While the equations for
the daughter modes resemble their first order classical uniform counterparts,
the parent mode is governed by a second order forced Duffing equation. It is
demonstrated that the solutions of those three coupled equations exhibit a wide
and rich spectrum of dynamical behavior. In particular, it is shown that
amplitudes of unstable triads may grow explosively with time, namely reaching
infinite values in a finite time. Paradoxically, explosively unstable near-
resonance triads may grow much faster than their strict-resonance counterparts.
