Deviations from an idealized equilibrium phase transition picture in nuclear multifragmentation is studied in terms of the entropic index. We investigate different heat-capacity features in the canonical quantum statistical fragmentation model generalized in the framework of non-extensive thermostatistics, and show that in this model the negative branch of heat capacity in quasi-peripheral Au+Au reactions is consistent with the dominance of non-extensive effects in these reactions.

PACS numbers: 25.70.Pq, 05.20.--y, 05.70.Jk, 24.60.Ky