  We address the formation of 3D nullpoint topologies in the solar corona by
combining Hinode/XRT observations of a small dynamic limb event, which occurred
beside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. To
this end, we model the boundary-driven kinematic emergence of a compact,
intense, and uniformly twisted flux tube into a potential field arcade that
overlies a weakly twisted coronal flux rope. The expansion of the emerging flux
in the corona gives rise to the formation of a nullpoint at the interface of
the emerging and the pre-existing fields. We unveil a two-step reconnection
process at the nullpoint that eventually yields the formation of a broad 3D
fan-spine configuration above the emerging bipole. The first reconnection
involves emerging fields and a set of large-scale arcade field lines. It
results in the launch of a torsional MHD wave that propagates along the
arcades, and in the formation of a sheared loop system on one side of the
emerging flux. The second reconnection occurs between these newly formed loops
and remote arcade fields, and yields the formation of a second loop system on
the opposite side of the emerging flux. The two loop systems collectively
display an anenome pattern that is located below the fan surface. The flux that
surrounds the inner spine field line of the nullpoint retains a fraction of the
emerged twist, while the remaining twist is evacuated along the reconnected
arcades. The nature and timing of the features which occur in the simulation do
qualititatively reproduce those observed by XRT in the particular event studied
in this paper. Moreover, the two-step reconnection process suggests a new
consistent and generic model for the formation of anemone regions in the solar
corona.
