  Inspired by recent measurement of possible fully charmed tetraquarks in LHCb
Collaboration, we investigate the mass spectra of fully heavy tetraquarks $QQ
\bar Q \bar Q$ in an extended relativized quark model. Our estimations indicate
that the broad structure around 6.4 GeV should contain one or more ground $cc
\bar c \bar c$ tetraquark states, while the narrow structure near 6.9 GeV can
be categorized as the first radial excitation of $cc \bar c \bar c$ system.
Moreover, with the wave functions of the tetraquarks and mesons, the strong
decays of tetraquarks into heavy quarkonium pair are qualitatively discussed,
which can be further checked by the LHCb and CMS Collaborations.
