  Enceladus is a primary target for astrobiology due to the $\rm H_2O$ plume
ejecta measured by the Cassini spacecraft and the inferred subsurface ocean
sustained by tidal heating. Sourcing the plumes via a direct connection from
the ocean to the surface requires a fracture through the entire ice shell
($\sim$10 km). Here we explore an alternative mechanism in which shear heating
within shallower tiger stripe fractures produces partial melting in the ice
shell and interstitial convection allows fluid to be ejected as geysers. We use
an idealized two-dimensional multiphase reactive transport model to simulate
the thermomechanics of a mushy region generated by an upper bound estimate for
the localized shear heating rate in a salty ice shell. From our simulations, we
predict the temperature, porosity, salt content, melting rate, and liquid
volume of an intrashell mushy zone surrounding a fracture. We find that the
rate of internal melting can match the observed $\rm H_2O$ eruption rate and
that there is sufficient brine volume within the mushy zone to sustain the
geysers for $\sim350$ kyr without additional melting. The composition of the
liquid brine is, however, distinct from that of the ocean, due to partial
melting. This shear heating mechanism for geyser formation applies to Enceladus
and other icy moons and has implications for our understanding of the
geophysical processes and astrobiological potential of icy satellites.
