Low T heat capacity measurements and new entropy data for titanite (sphene): implications for thermobarometry of high-pressure rocks
Low T heat capacity measurements and new entropy data for titanite (sphene): implications for thermobarometry of high-pressure rocks
复制标题
钛矿（榍石）的低 T 热容测量和新熵数据：对高压岩石热压测量的影响
DOI：
10.1007/s00410-008-0311-3
复制
发表时间：
2008
影响因子：
3.5
通讯作者：
E. Essene
中科院分区：
文献类型：
--
作者：
M. Manon;E. Dachs;E. Essene
钛铁矿的标准态熵在最近的几个研究中受到了质疑，建议从文献值129.3±0.8J/molK修正为110-120J/molK。因此，用PPMS在5-300K范围内重新测量了钛铁矿的热容，计算出钛铁矿的标准态熵为127.2±0.2J/molK，比建议的修正更接近原始数据。修正的Murgnahan状态方程的体积参数：Vp，T=V298°T×−[1°+−°(T−(298)]=20a°(T−(298)])×−[1/4(1°-11.5×10−4[T−(298])+4p)]1/4与最近高温高压下的单胞测定相吻合，得到常数V298°=5.568 J/bar，a°=3.1J/bar，a°=3.1J×10−5K−1，K=1100KBAR。根据新的熵和体积数据，结合钛矿+蓝晶石+金红石反应的实验数据，计算出钛矿的标准吉布斯生成自由能−为2456.2 kJ/m ol(∆H°f=−2598.4 kJ/m o l)。这个值比实验测定的生成热值要小4-11kJ/mol，比内部一致的数据库中给出的值稍负一些。大多数与钛铁矿有关的计算相平衡的位移不大，但与小∆S的反应除外。重新计算了几个变质岩套的Baric估算值，榴辉岩的压力差约为2kbar，超高压含钛组合的压力差约为10kbar。
The accepted standard state entropy of titanite (sphene) has been questioned in several recent studies, which suggested a revision from the literature value 129.3 ± 0.8 J/mol K to values in the range of 110–120 J/mol K. The heat capacity of titanite was therefore re-measured with a PPMS in the range 5 to 300 K and the standard entropy of titanite was calculated as 127.2 ± 0.2 J/mol K, much closer to the original data than the suggested revisions. Volume parameters for a modified Murgnahan equation of state:VP,T=V298° × [1 + a°(T− 298) − 20a°(T− 298)] × [1 – 4P/(K298× (1 – 1.5 × 10−4[T− 298]) + 4P)]1/4were fit to recent unit cell determinations at elevated pressures and temperatures, yielding the constantsV298° = 5.568 J/bar,a° = 3.1 × 10−5K−1, andK= 1,100 kbar. The standard Gibbs free energy of formation of titanite, −2456.2 kJ/mol (∆H°f= −2598.4 kJ/mol) was calculated from the new entropy and volume data combined with data from experimental reversals on the reaction, titanite + kyanite = anorthite + rutile. This value is 4–11 kJ/mol less negative than that obtained from experimental determinations of the enthalpy of formation, and it is slightly more negative than values given in internally consistent databases. The displacement of most calculated phase equilibria involving titanite is not large except for reactions with small ∆S. Re-calculated baric estimates for several metamorphic suites yield pressure differences on the order of 2 kbar in eclogites and 10 kbar for ultra-high pressure titanite-bearing assemblages.
影响因子：
3.7
作者：
R. L. King;G. Bebout;K. Kobayashi;E. Nakamura;Sebastiaan N. G. C. van der Klauw
通讯作者：
R. L. King;G. Bebout;K. Kobayashi;E. Nakamura;Sebastiaan N. G. C. van der Klauw