Chemical diffusion of Ca has been characterized in natural enstatite under buffered conditions (IW, NNO) and in air. Experiments were conducted using synthesized powder sources, with Ca diffusion profiles measured with Rutherford Backscattering Spectrometry. A variety of sources of diffusant were used to investigate the effects of silica activity and Ca concentration on diffusion. Calcium diffusion appears relatively insensitive to crystallographic orientation and oxygen fugacity under the range of investigated conditions, and also appears little influenced by differences in silica activity and Ca concentration in the diffusant source. For Ca diffusion in a natural enstatite, we obtain the following Arrhenius relation for diffusion over the temperature range 750 – 1150°C,

D = 1.17x10^-10exp(-240 ± 10 kJ mol^-1/RT) m²sec^-1 .

Calcium diffusion is slower than Mg, Cr and Fe in enstatite, but faster than larger divalent cations Pb and Eu that also are likely to preferentially occupy the M2 site. Calcium diffusion is also faster than that for trivalent REE and tetravalent Ti in enstatite. Calcium diffusivities in enstatite are intermediate between Ca diffusivities in clinopyroxene and olivine, with Ca diffusion in enstatite about 2 orders of magnitude faster than Ca self-diffusion in diopside and 2 orders of magnitude slower than Ca diffusion in olivine.

Diffusion parameters obtained from this study were used to develop a simple model for closure temperature of the Ca-in-opx thermometer of Brey and Köhler (1990). By coupling closure temperature and the Ca-in-opx thermometer, it is possible to constrain cooling rates of peridotites and pyroxenites. Applications to peridotites from the Lanzo Massif and the Oman ophiolite are presented.

在缓冲条件（IW、NNO）和空气中，Ca 的化学扩散已在天然顽火辉石中进行了表征。使用合成粉末源进行实验，用卢瑟福背散射光谱法测量 Ca 扩散曲线。使用多种扩散剂来源来研究二氧化硅活性和 Ca 浓度对扩散的影响。在所研究的条件范围内，钙扩散似乎对晶体取向和氧逸度相对不敏感，并且似乎几乎不受扩散剂源中二氧化硅活性和 Ca 浓度差异的影响。对于天然顽火辉石中的 Ca 扩散，我们在 750 – 1150°C 的温度范围内获得以下扩散的 Arrhenius 关系，

D = 1.17x10 ^-10 exp(-240 ± 10 kJ mol ^-1 /RT) m ² sec ^-1。

钙在顽火辉石中的扩散比 Mg、Cr 和 Fe 慢，但比也可能优先占据 M2 位点的较大二价阳离子 Pb 和 Eu 快。钙的扩散也比顽火石中的三价 REE 和四价 Ti 快。顽火辉石中的钙扩散率介于单斜辉石和橄榄石中的 Ca 扩散率之间，顽火辉石中的 Ca 扩散比透辉石中的 Ca 自扩散快约 2 个数量级，比橄榄石中的 Ca 扩散慢 2 个数量级。

从这项研究中获得的扩散参数用于开发 Brey 和 Köhler (1990) 的 Ca-in-opx 温度计的闭合温度的简单模型。通过耦合闭合温度和 Ca-in-opx 温度计，可以限制橄榄岩和辉石岩的冷却速率。介绍了兰佐地块和阿曼蛇绿岩对橄榄岩的应用。