白云石有序度与流变特征的研究进展

白云石CaMg(CO3)2常见于白云岩、灰岩及大理岩中，其稳定的温压范围很广，是研究俯冲隧道变形、全球碳循环和地幔交代作用的重要矿物。白云石的有序度可能与重结晶过程相关，温度是影响白云石有序度的关键因素，压力对白云石有序度的影响较弱。在1~3 GPa 下白云石完全无序的转变温度为1150~1200℃，Fe、Mn、Cd 离子含量的增高可显著降低白云石结构无序化的转变温度。天然变形的白云石常发育由底面c 滑移控制的晶格优选定向。根据白云石的流变律，在天然应变速率下（10-15~10-12 s-1），>400℃细粒白云石以扩散蠕变为主；而粗粒白云石以位错蠕变为主，只有在高温下（>600~700℃） 扩散蠕变才成为主控变形机制。分解反应或者动态重结晶可导致白云石流变强度的显著下降，应变集中。白云石c滑移的临界剪应力随温度升高而增大的现象可能与白云石有序度的变化有关，而围压、水逸度和成分对白云石流变的影响尚不清楚，定量研究白云石的有序度与流变学性质的相关性将为追踪碳酸盐岩和大理岩的成岩和变形历史提供新的信息。

Research Progress on Ordering and Rheological Properties of Dolomite

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.