  We report the detection of extended (>0.5-1kpc) high-ionization [MgIV] 4.487
$\mu$m (80 eV) emission in four local luminous infrared galaxies observed with
JWST/NIRSpec. Excluding the nucleus and outflow of the Type 1 active galactic
nucleus (AGN) in the sample, we find that the [MgIV] luminosity is well
correlated with that of H recombination lines, which mainly trace star forming
clumps in these objects, and that the [ArVI] 4.530 $\mu$m (75 eV), usually seen
in AGN, is undetected. On 100-400pc scales, the [MgIV] line profiles are
broader (sigma([MgIV])=90 +- 25 km/s) and shifted (Delta_v up to +- 50 km/s)
compared to those of the H recombination lines and lower ionization transitions
(e.g., sigma(Hu-12)=57 +- 15 km/s). The [MgIV] kinematics follow the large
scale rotating velocity field of these galaxies and the broad [MgIV] profiles
are compatible with the broad wings detected in the H recombination lines.
Based on these observational results, extended highly ionized gas more
turbulent than the ambient interstellar medium, possibly as a result of
ionizing shocks associated with star-formation, is the most likely origin of
the [MgIV] emission. We also computed new grids of photoionization and shock
models to investigate where the [MgIV] line originates. Shocks with velocities
of 100-130 km/s reproduce the observed line ratios and the [MgIV] luminosity
agrees with that expected from the mechanical energy released by supernove
(SNe) in these regions. Therefore, these models support shocks induced by SNe
as the origin of the [MgIV] line. Future studies on the stellar feedback from
SNe will benefit from the [MgIV] line that is little affected by obscuration
and, in absence of an AGN, can only be produced by shocks due to its high
ionization potential.
