  We study the spreading of entanglement produced by the time evolution of a
local fermionic excitation created above the ground state of the XXZ chain. The
resulting entropy profiles are investigated via density-matrix renormalization
group calculations, and compared to a quasiparticle ansatz. In particular, we
assume that the entanglement is dominantly carried by spinon excitations
traveling at different velocities, and the entropy profile is reproduced by a
probabilistic expression involving the density fraction of the spinons reaching
the subsystem. The ansatz works well in the gapless phase for moderate values
of the XXZ anisotropy, eventually deteriorating as other types of quasiparticle
excitations gain spectral weight. Furthermore, if the initial state is excited
by a local Majorana fermion, we observe a nontrivial rescaling of the entropy
profiles. This effect is further investigated in a conformal field theory
framework, carrying out calculations for the Luttinger liquid theory. Finally,
we also consider excitations creating an antiferromagnetic domain wall in the
gapped phase of the chain, and find again a modified quasiparticle ansatz with
a multiplicative factor.
