  A near-symplectic structure on a 4-manifold is a closed 2-form that is
symplectic away from the 1-dimensional submanifold along which it vanishes and
that satisfies a certain transversality condition along this vanishing locus.
We investigate near-symplectic 4-manifolds equipped with singular Lagrangian
torus fibrations which are locally induced by effective Hamiltonian torus
actions. We show how such a structure is completely characterized by a singular
integral affine structure on the base of the fibration whenever the vanishing
locus is nonempty. The base equipped with this geometric structure generalizes
the moment map image of a toric 4-manifold in the spirit of earlier work by the
second author on almost toric symplectic 4-manifolds. We use the geometric
structure on the base to investigate the problem of making given smooth torus
actions on 4-manifolds symplectic or Hamiltonian with respect to
near-symplectic structures and to give interesting constructions of structures
which are locally given by torus actions but have nontrivial global monodromy.

Symplectic Geometry;Geometric Topology