  Protoplanets growing within the protoplanetary disk by pebble accretion
acquire hydrostatic gas envelopes. Due to accretion heating, the temperature in
these envelopes can become high enough to sublimate refractory minerals which
are the major components of the accreted pebbles. Here we study the sublimation
of different mineral species and determine whether sublimation plays a role
during the growth by pebble accretion. For each snapshot in the growth process,
we calculate the envelope structure and sublimation temperature of a set of
mineral species representing different levels of volatility. Sublimation lines
are determined using and equilibrium scheme for the chemical reactions
responsible for destruction and formation of the relevant minerals. We find
that the envelope of the growing planet reaches temperatures high enough to
sublimate all considered mineral species when the mass is larger than 0.4 Earth
masses. The sublimation lines are located within the gravitionally bound
envelope of the planet. We make a detailed analysis of the sublimation of FeS
at around 720 K, beyond which the mineral is attacked by H2 to form gaseous H2S
and solid Fe. We calculate the sulfur concentration in the planet under the
assumption that all sulfur released as H2S is lost from the planet by diffusion
back to the protoplanetary disk. Our calculated values are in good agreement
with the slightly depleted sulfur abundance of Mars, while the model
overpredicts the extensive sulfur depletion of Earth by a factor of
approximately 2. We show that a collision with a sulfur-rich body akin to Mars
in the moon-forming impact lifts the Earth's sulfur abundance to approximately
10% of the solar value for all impactor masses above 0.05 Earth masses.
