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The hydrogen mobilities in andradite and zircon were investigated by performing H-D exchange experiments under ambient pressure in a horizontal furnace flushed with a gas mixture of Ar/D2(10％).The temperature range investigated was 400-700 ℃ for andradite and 900-1150 ℃ for zircon.The andradite samples are single crystals from an iron-skarn deposit on Serifos island, Greece, while the zircon samples are single crystals from Madagascar.FTIR analyses were performed before and after each annealing run.At contrary to the same type of experiments performed in NAMs, it was not possible to replace all hydrogen atoms in the structure by deuterium, 15％ to 35％ for andradite and 25％ to 40％ for zircon of OH remaining after completion of the exchange.However, a steady-state equilibrium was reached at the end of the experiments and it was possible to determine the diffusion law of the exchange process.In andradite, all bands follow the same kinetics regarding exchange of H by D (H-D exchange) or D by H (D-H exchange), with diffusion law:D0 exp[(96 ± 11)kJ/mol/RT]with logD0 (in m2/s) =-5.9 ± 0.7.The activation energy is similar to those of hydrogen diffusion in grossular, but the diffusivity is more than 2 orders of magnitude faster.Our results demonstrate that, composition has a major effect on H diffusion and it must be considered in any discussion of δD signatures in garnets.In andradite-rich garnets, hydrogen isotope data can only be used to record short, low-grade metamorphic or metasomatic events, at temperatures lower than 400 ℃.In zircon, hydrogen diffusion is anisotropic, slightly faster along [001] than along [100] and [010]:D[100][010]=D0exp[-(374±39)kJ/mol/RT]with log D0 (m2s-1) =2.24 ± 1.57.D[001] =D0 exp[-(334±49)kJ/mol/RT] with log D0 (m2s-1) =1.11 ±0.22.H diffusion in zircon has much higher activation energy and slower diffusivity thanother NAMs.During H-D exchange zircon incorporates also deuterium.For the first time, the hydration reaction U5+ + OH =U4+ + O2-+ 1/2H2, involving uranium reduction is observed.The kinetics of deuterium incorporation is just slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen diffusion.It confirms that hydrogen isotopic memory of zircon is higher than other NAMs.Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures.At 500 ℃, a zircon with a radius of 300μm would retain its H isotopic signature over more than a million years.