A Comprehensive Solution Model for Complex FeTi Oxides Relevant to Thermobarometry

Ghiorso和evans华盛顿大学-本项目将使用实验相平衡结合热力学建模来修正和扩展FeTi氧化物温度计的功能。这种温度计是用来推断某些岩石形成条件的主要工具。它使用铁钛氧化物（一种菱形氧化物与尖晶石共存）平衡对的组成来估计矿物组合最终平衡的温度和氧逸度（fO2）条件。最近的实验研究表明，对于超过镍镍氧化物氧缓冲液的条件，目前的温度计配方是失败的。此外，在建立和校准现有热气压计的热力学模型之后，新的实验工作已经发表，修正了远程阳离子有序的估计，并大大澄清了短程有序的性质以及菱形相中对称驱动相变的特征。总之，这些研究推动了对热气压计的热力学公式的修订，使其具有更完善的理论基础，并解决了在更多氧化共生岩，特别是造山弧岩浆中估计T-fO2的实际必要性。修订后的地温计将作为一个独立的基于网络的软件产品分发。

AbstractEAR-0207475 Ghiorso and EvansUniversity of WashingtonThis project will use experimental phase equilibria combined with thermodynamic modeling to revise and extend the capabilities of the FeTi oxide thermobarometer. This thermobarometer is a primary tool used to infer conditions under which certain rocks form. It uses compositions of equilibrium pairs of Fe-Ti oxides (a rhombohedral oxide coexisting with a spinel) to derive estimates of temperature and oxygen fugacity (fO2) conditions under which a mineral assemblage last equilibrated. Recent experimental studies have demonstrated the failure of current formulations of the thermobarometer for conditions that exceed the nickel nickel-oxide oxygen buffer. In addition, subsequent to the formulation and calibration of the thermodynamic models that underlie the existing thermobarometer, new experimental work has been published revising estimates of long-range cation order and greatly clarifying the nature of short-range ordering as well as the character of the symmetry-driven phase transition in the rhombohedral phase. Together, these studies motivate a revision of the thermodynamic formulation of the thermobarometer to place it on sounder theoretical footing and to address the practical necessity of estimating T-fO2 in more oxidized parageneses, in particular orogenic arc magmas. The revised geothermometer will be distributed as a standalone and web-based software product.