关键词: 白云石, 有序度, 晶格优选定向, 位错蠕变, 扩散蠕变

Abstract: Dolomite CaMg(CO3)2 widely occurs in dolostone, limestone and marble. The wide P-T stability conditions of dolomite make it an important mineral for understanding deformation in subduction channels, global carbon cycle and mantle metasomatism. The degree of cation order in dolomite probably relates with recrystallization process. Cation ordering in dolomite is controlled by temperature, and weakly dependent on pressure. At pressure of 1-3 GPa, complete disordering in dolomite is achieved at 1150-1200℃. The addition of Fe, Mn and Cd could significantly decrease the order/disorder transition temperature of dolomite. Naturally deformed dolomite often develops the crystallographic preferred orientation due to activation of c slip. According to flow laws of dolomite, under the natural strain rate of 10-15-10-12 s-1, diffusion creep is the dominant deformation mechanism in fine-grained dolomite above 400℃ and in coarse-grained dolomite above 600-700℃. Below these temperature, dislocation creep controls ductile deformation of dolomite. Decomposition reaction or dynamic recrystallization can significantly decrease strength of dolomite and results in strain localization. The increasing of critical shear stress of c slip in dolomite with increasing temperature may be related with the cation order. The influence of confining pressure, water fugacity and composition on rheology of dolomite is still not clear. Quantitative study of the correlation between cation order and rheological properties of dolomite will provide new information to trace petrogenesis and deformation history of carbonates and marble.

Key words: dolomite, cation order, crystallographic preferred orientation, dislocation creep, diffusion creep