  On the basis of the extensive air shower (EAS) data obtained by the GAMMA
experiment, the energy spectra and elemental composition of the primary cosmic
rays are derived in the 1-100 PeV energy range. The reconstruction of the
primary energy spectra is carried out using an EAS inverse approach in the
framework of the SIBYLL2.1 and QGSJET01 interaction models and the hypothesis
of power-law primary energy spectra with rigidity-dependent knees. The energy
spectra of primary H, He, O-like and Fe-like nuclei obtained with the SIBYLL
interaction model agree with corresponding extrapolations of the balloon and
satellite data to ~1 PeV energies. The energy spectra obtained from the QGSJET
model show a predominantly proton composition in the knee region. The
rigidity-dependent knee feature of the primary energy spectra for each
interaction model is displayed at the following rigidities: ~2.5+/-0.2 PV
(SIBYLL) and ~3.1-4.2 PV (QGSJET). All the results presented are derived taking
into account the detector response, the reconstruction uncertainties of the EAS
parameters, and fluctuations in the EAS development.
