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Experimental and thermodynamic constraints on mineral equilibrium in pantelleritic magmas
Lithos ( IF 3.5 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.lithos.2020.105793
Pierangelo Romano , Bruno Scaillet , John C. White , Joan Andújar , Ida Di Carlo , Silvio G. Rotolo

Abstract Crystallization experiments on two pantellerites from Pantelleria, Italy, provide new evidence for the relationships between mineral phases in pantelleritic rocks as well as the influence of temperature and redox conditions on mineral assemblages. Experiments were performed at 1 kbar with temperature ranging between 750–900°C, and fluid saturation conditions with XH2O (=H2O/H2O+CO2) between 0 and 1. Redox conditions were fixed at, or slightly below, the FMQ buffer. Results show that at temperature of 900 °C pantelleritic magmas are well above the liquidus regardless their water content; we also observed a decrease in liquidus temperature (800°C) with increasingly reducing conditions. Mineral assemblages of the natural rocks have been successfully reproduced, particularly the relationship between fayalite and aenigmatite, which appear to be strongly controlled by melt peralkalinity, temperature and redox conditions. This is the first time that fayalitic olivine have been synthetized in experimental studies on pantellerites, which was found to be stable only for temperatures ≥750°C while amphibole can be stable at temperatures as high as 800°C at high fF2. Experimental results have been compared with the composition of mineral phases as well as with the results obtained from mineral equilibrium, geothermometry, and oxygen barometry studies on pantelleritic lava and tuffs from Pantelleria (Italy), Eburru (Kenya) and Menengai (Kenya). Petrological characteristics appear similar at different locations worldwide, with typical assemblages of anorthoclase and sodian clinopyroxene with variable fayalite, aenigmatite, Fe-Ti oxides and amphibole.

中文翻译:

泛碱岩浆矿物平衡的实验和热力学约束

摘要 意大利潘泰莱里亚 (Pantelleria) 的两种 pantellerite 的结晶实验为 pantellerite 岩石中矿物相之间的关系以及温度和氧化还原条件对矿物组合的影响提供了新的证据。实验在 1 kbar 下进行,温度范围在 750–900°C 之间,流体饱和条件为 XH2O (=H2O/H2O+CO2) 介于 0 和 1 之间。氧化还原条件固定在或略低于 FMQ 缓冲液。结果表明,在 900 °C 的温度下,泛碱岩浆远高于液相线,无论其含水量如何;我们还观察到液相线温度 (800°C) 随着条件不断降低而降低。已成功再现天然岩石的矿物组合,特别是铁橄榄石与蛇纹岩之间的关系,这似乎受到熔体过碱度、温度和氧化还原条件的强烈控制。这是第一次在 pantellerites 的实验研究中合成铁橄榄石,发现它仅在 750°C 以上的温度下稳定,而角闪石在高 fF2 的温度下可以稳定在 800°C。实验结果已与矿物相的组成以及从 Pantelleria(意大利)、Eburru(肯尼亚)和 Menengai(肯尼亚)的 pantellerite 熔岩和凝灰岩的矿物平衡、地温测量和氧气压研究中获得的结果进行了比较。世界各地不同地点的岩石学特征似乎相似,具有典型的斜长石和钠斜辉石组合,具有可变的铁橄榄石、蛇纹岩、Fe-Ti 氧化物和角闪石。
更新日期:2020-12-01
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