  In inhomogeneous cosmology, restricting attention to an irrotational dust
matter model, backreaction arises in terms of the deviation of the averaged
spatial scalar curvature from a constant-curvature model on some averaging
domain $D$, $W_D$, and the kinematical backreaction $Q_D$. These backreaction
variables can be modeled as an effective scalar field, called the `morphon
field'. The general cosmological equations still need a closure condition to be
solved. A simple example is the class of scaling solutions where $W_D$ and
$Q_D$ are assumed to follow a power law of the volume scale factor $a_D$. But
while they can describe models of quintessence, these and other models still
assume the existence of dark matter in addition to the known sources. Going
beyond scaling solutions by using a model for structure formation that we argue
is reasonably generic, we investigate the correspondence between the morphon
field and fundamental scalar field dark matter models, in order to describe
dark matter as an effective phenomenon arising from kinematical backreaction
and the averaged spatial curvature of the inhomogeneous Universe. While we find
significant differences with those fundamental models, our main result is that
the energy budget on typical collapsing domains is provided by curvature and
matter in equal parts already around the turn-around time, leading to curvature
dominance thereafter and increasing to a curvature contribution of $3/4$ of the
energy budget at the onset of virialization. Kinematical backreaction is
subdominant at early stages, but its importance rises quickly after turn-around
and dominates the curvature contribution in the final phase of the collapse. We
conclude that backreaction can indeed mimic dark matter (in the energy budget)
during the collapse phase of megaparsec-scale structures.
