A revised diamond-graphite transition curve
A revised diamond-graphite transition curve
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DOI：
10.2138/am.2011.3763
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发表时间：
2012-01-01
影响因子：
3.1
通讯作者：
Day, Howard W.
中科院分区：
文献类型：
--
作者：
Day, Howard W.
从金刚石到石墨的转变是解释超高压变质岩的关键平衡。尽管引起了广泛的兴趣，P 和 T 的最佳可用实验测定（Kennedy 和 Kennedy 1976）与许多转变的热力学计算之间仍然存在显着的系统差异。在低于 1400 K 的温度下，计算出的平衡压力比实验的外推值低 5 kbar。在 3000 K 时，计算出的压力范围从高于推断转变位置 8 kbar 到低于推断转变位置近 20 kbar。基于对实验和热力学数据的严格审查的修订曲线与扩展的实验范围和首选的量热数据一致。它比 Kennedy 和 Kennedy (1976) 提出的转变以及之前的计算更陡峭，并经过 16.2 kbar、298 K； 33.9 kbar，1000 K； 63.5 kbar，2000 K；和 98.4 kbar，3000 K。修正后的曲线意味着形成含金刚石地壳岩石的最小压力比实验外推所暗示的小 3-4 kbar。由于修改后的转变比之前的大多数计算更陡峭，因此石墨、金刚石和液态碳之间的三相点可能比之前估计的高出 40 kbar。
The transition from diamond to graphite is a key equilibrium for interpreting ultrahigh-pressure metamorphic rocks. Despite widespread interest, there remain significant systematic differences between the best available experimental determinations of P and T(Kennedy and Kennedy 1976) and numerous thermodynamic calculations of the transition. At temperatures below 1400 K, calculated equilibrium pressures are lower than extrapolations of the experiments by as much as 5 kbar. At 3000 K, calculated pressures vary from more than 8 kbar above to almost 20 kbar below the position of the extrapolated transition. A revised curve based on a critical review of the experimental and thermodynamic data is consistent with expanded experimental brackets and the preferred calorimetric data. It is steeper than the transition proposed by Kennedy and Kennedy (1976) and previous calculations and passes through 16.2 kbar, 298 K; 33.9 kbar, 1000 K; 63.5 kbar, 2000 K; and 98.4 kbar, 3000 K.The revised curve implies that the minimum pressure for formation of diamond-bearing crustal rocks is 3-4 kbar less than implied by extrapolation of the experiments. Because the revised transition is steeper than most previous calculations, the triple point among graphite, diamond, and liquid carbon may be as much as 40 kbar higher than previously estimated.