Time-resolved coherent anti-Stokes Raman scattering is applied to prepare and interrogate vibrational coherences on the ground electronic surface of molecular iodine isolated in Ar matrices. The coherence decay time shows a linear dependence on vibrational quantum numbers, for v = 3 - 15. The temperature dependence of decoherence rates is negligible for <$E v~<<~7>, in the experimental range T = 18 - 32 K. For a v = 13, 14 superposition, the temperature dependence indicates dephasing by a 66 <$E roman cm sup -1> pseudo-local phonon, just outside the Debye edge of the solid. The accuracy of the data is limited due to two-photon induced dissociation of the molecule, which process is characterized using polarized fields. The <$E T~symbol О~0> limit of dephasing is discussed.