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首页> 外文期刊>Contributions to Mineralogy and Petrology >The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep
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The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep

机译：溶解镁对方解石II蠕变的影响：从扩散蠕变到位错蠕变

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We extended a previous study on the influence of Mg solute impurity on diffusion creep in calcite to include deformation under a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2-30 h) at 850 deg C and 300 MPa confining pressure. The HIP treatment resulted in high-magncsian calcite aggregates with Mg content ranging from 0.5 to 17 mol percent. Both back-scattered electron images and chemical analysis suggested that the dolomite phase was completely dissolved, and that Mg distribution was homogeneous throughout the samples at the scale of about two micrometers. The grain size after HIP varied from 8 to 31 mu m, increased with time at temperature, and decreased with increasing Mg content (>3.0 mol percent). Grain size and time were consistent with a normal grain growth equation, with exponents from 2.4 to 4.7, for samples containing 0.5-17.0 mol percent Mg, respectively. We deformed samples after HIP at the same confining pressure with differential stresses between 20 and 200 MPa using either constant strain rate or stepping intervals of loading at constant stresses in a Paterson gas-medium deformation apparatus. The deformation tests took place at between 700 and 800 deg C and at strain rates between 10~(-6) and 10~(-3) s~(-1). After deformation to strains of about 25 percent, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The deformation data indicated a transition in mechanism from diffusion creep to dislocation creep. At stresses below 40 MPa, the strength was directly proportional to grain size and decreased with increasing Mg content due to the reductions in grain size. At about 40 MPa, the sensitivity of log strain rate to log stress, (n), became greater than 1 and eventually exceeded 3 for stresses above 80 MPa. At a given strain rate and temperature, the stress at which that transition occurred was larger for samples with higher Mg content and smaller grain size. At given strain rates, constant temperature, and fixed grain size, the strength of calcite in the dislocation creep regime increased with solute content, while the strength in the diffusion creep regime was independent of Mg content. The results suggest that chemical composition will be an important element to consider when solid substitution can occur during natural deformation.
机译：我们扩展了对镁溶质杂质对方解石扩散蠕变影响的先前研究，以包括在更宽的应力条件范围和更宽的镁含量范围内的变形。通过在850℃和300 MPa的围压下，以不同间隔（2-30小时）对方解石粉和白云石粉进行热等静压（HIP）混合物来生产合成大理石。经HIP处理后，镁含量高的方解石聚集体的Mg含量为0.5至17 mol％。反向散射电子图像和化学分析均表明白云石相已完全溶解，并且整个样品中Mg的分布在大约2微米的范围内是均匀的。 HIP后的晶粒尺寸从8到31μm不等，在温度下随时间增加，而随着Mg含量（> 3.0 mol％）增加而减小。含0.5-17.0 mol％Mg的样品的晶粒尺寸和时间与正常晶粒生长方程式一致，指数从2.4到4.7。在帕特森气体介质变形装置中，我们采用恒定应变率或恒定应力加载的步进间隔，在相同的约束压力下，在相同的约束压力下，以相同的约束压力使样品变形，变形率为20到200 MPa。变形试验在700至800摄氏度之间进行，应变率在10〜（-6）和10〜（-3）s〜（-1）之间。变形至约25％的应变后，在较高应力下加载的一些样品中，大的原胚细胞和小的重结晶的新胚细胞共存双峰分布。变形数据表明机理从扩散蠕变到位错蠕变。在低于40 MPa的应力下，强度与晶粒尺寸成正比，并且由于晶粒尺寸的减小而随Mg含量的增加而降低。在约40 MPa时，对数应变速率对对数应力（n）的灵敏度变得大于1，最终对于80 MPa以上的应力超过3。在给定的应变速率和温度下，具有较高Mg含量和较小晶粒尺寸的样品，发生转变的应力较大。在给定的应变速率，恒定的温度和固定的晶粒尺寸下，位错蠕变态下的方解石强度随溶质含量的增加而增加，而扩散蠕变态下的方解强度与镁含量无关。结果表明，当自然变形过程中发生固体置换时，化学成分将成为重要的考虑因素。

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