We performed creep experiments on synthetic fine-grained polycrystalline anorthite (d<30 &mgr;m) at temperatures from T=1000 ¿C to 1300 ¿C, oxygen fugacities of fO2=10-19--10-4 MPa, and stresses of &sgr;=5--80 MPa at room pressure. Experimental results show creep with high strain-rate sensitivity for stresses below &sgr;<30 MPa. We found the empirical flow law: ϵ=(3.8¿11.5)¿1010&sgr;13¿0.3d-2.5¿0.3¿exp(-420¿38 kJ/mol/RT) Transmission electron microscopy shows that the material is free of melt. The dislocation density is less than 1¿108 cm-2. We suggest that the samples deformed in diffusion-controlled grain size sensitive creep. ¿ American Geophysical Union 1996