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首页> 外文期刊>Contributions to Mineralogy and Petrology >Fe-Mg interdiffusion rates in clinopyroxene: experimental data and implications for Fe-Mg exchange geothermometers
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Fe-Mg interdiffusion rates in clinopyroxene: experimental data and implications for Fe-Mg exchange geothermometers

机译：Fe-Mg在辉石中的互扩散速率：实验数据及其对Fe-Mg交换地热仪的影响

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Chemical interdiffusion of Fe-Mg along the c-axis [001] in natural diopside crystals (X_(Di) = 0.93) was experimentally studied at ambient pressure, at temperatures ranging from 800 to 1,200 °C and oxygen fugacities from 10~(-11) to 10~(-17) bar. Diffusion couples were prepared by ablating an olivine (X_(Fc) = 0.3) target to deposit a thin film (20-100 nm) onto a polished surface of a natural, oriented diopside crystal using the pulsed laser deposition tech nique. After diffusion anneals, compositional depth profiles at the near surface region (~400 nm) were measured using Rutherford backscattering spectroscopy. In the experi mental temperature and compositional range, no strong dependence of D~(Fe-Mg) on composition of clinopyroxene (Fe/Mg ratio between Di_(93)-Di_(65)) or oxygen fugacity could be detected within the resolution of the study. The lack of fO_2~dependence may be related to the relatively high Al content of the crystals used in this study. Diffusion coef ficients, D~(Fe-Mg), can be described by a single Arrhenius relation with D~(Fe-Mg)=2.77±4.27×10~(-7)exp(-320.7±16.0kj/mol/RT)m~2/s D~(Fe-Mg) in clinopyroxene appears to be faster than diffusion involving Ca-species (e.g., D~(Ca-Mg)) while it is slower than D~(Fe-Mg) in other common mafic minerals (spinel, olivine, garnet, and orthopyroxene). As a consequence, diffusion in clinopyroxene may be the rate-limiting process for the freezing of many geothermometers, and compositional zoning in clinopyroxene may preserve records of a higher (compared to that preserved in other coexisting mafic minerals) temperature segment of the thermal history of a rock. In the absence of pervasive recrystallization, clino pyroxene grains will retain compositions from peak tem peratures at their cores in most geological and planetary settings where peak temperatures did not exceed ~l,100°C (e.g., resetting may be expected in slowly cooled mantle rocks, many plutonic mafic rocks, or ultra-high temperature metamorphic rocks).
机译：在环境压力，温度范围为800至1,200°C，氧逸度为10〜（-）的条件下，实验研究了Fe-Mg在天然透辉石晶体（X_（Di）= 0.93）中沿c轴[001]的化学扩散。 11）至10〜（-17）bar。通过使用脉冲激光沉积技术烧蚀橄榄石（X_（Fc）= 0.3）靶材以在自然取向的透辉石晶体的抛光表面上沉积薄膜（20-100 nm），从而制备扩散对。扩散退火后，使用卢瑟福反向散射光谱仪在近表面区域（约400 nm）测量成分深度分布。在实验温度和组成范围内，D〜（Fe-Mg）对斜辉石的组成（Di_（93）-Di_（65）之间的Fe / Mg比）或氧逸度均无强烈依赖性。研究。缺乏fO_2依赖性可能与本研究中所用晶体的较高Al含量有关。扩散系数D〜（Fe-Mg）可以通过单个Arrhenius关系来描述，其中D〜（Fe-Mg）= 2.77±4.27×10〜（-7）exp（-320.7±16.0kj / mol / RT斜茂铁中的）m〜2 / s D〜（Fe-Mg）似乎快于涉及Ca物种（例如D〜（Ca-Mg））的扩散，而慢于其他物种中的D〜（Fe-Mg）扩散。常见的铁镁质矿物（尖晶石，橄榄石，石榴石和邻苯二甲酚）。结果，在次氯苯比芬中的扩散可能是许多地热仪冻结的限速过程，并且在次氯苯比芬中的成分分区可以保留更高温度（与其他共存的铁镁质矿物中保存的相比）的温度记录。一块石头。在没有普遍的重结晶的情况下，单斜辉石颗粒将在大多数地质和行星环境中在其峰值温度不超过约1100°C的环境中保留其峰值温度组成的成分（例如，在缓慢冷却的地幔岩石中可能会发生重置） ，许多深部镁铁质岩或超高温变质岩）。

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