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首页> 外文期刊>Contributions to Mineralogy and Petrology >Experimental determination of coexisting iron-titanium oxides in the systems FeTiAlO, FeTiAlMgO, FeTiAIMnO, and FeTiAlMgMnO at 800 and 900 deg C, 1-4 kbar, and relatively high oxygen fugacity
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Experimental determination of coexisting iron-titanium oxides in the systems FeTiAlO, FeTiAlMgO, FeTiAIMnO, and FeTiAlMgMnO at 800 and 900 deg C, 1-4 kbar, and relatively high oxygen fugacity

机译：实验测定FeTiAlO，FeTiAlMgO，FeTiAIMnO和FeTiAlMgMnO系统中在800和900摄氏度，1-4 kbar和相对较高的氧逸度下共存的铁钛氧化物

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摘要

A synthetic, low-melting rhyolite composition containing TiO_2 and iron oxide, with further separate additions of MgO, MnO, and MgO + MnO, was used in hydrothermal experiments to crystallize Ilm-Hem and Usp-Mt solid solutions at 800 and 900 deg C under redox conditions slightly below nickel-nickel oxide (NNO) to approx = 3 Iog_(10)f_(O_2) units above the NNO oxygen buffer. These experiments provide calibration of the FeTi-oxide thermometer + oxygen barometer at conditions of temperature and oxygen fugacity poorly covered by previous equilibrium experiments. Isotherms for our data in Roozeboom diagrams of projected percent usp vs. percent ilm show a change in slope at w 60 percent ilm, consistent with the second-order transition from FeTi-ordered Ilm to FeTi-disordered Ilm-Hem. This feature of the system accounts for some, but not all, of the differences from earlier thermodynamic calibrations of the thermoba-rometer. In rhyolite containing 1.0 wt percent MgO, 0.8 wt. percent MnO, or MgO + MnO, Usp-Mt crystallized with up to 14 percent of aluminate components, and Ilm-Hem crystallized with up to 13 percent geikielite component and 17 percent pyrophanite component. Relative to the FeTiAlO system, these components displace the ferrite components in Usp-Mt, and the hematite component in Ilm-Hem. As a result, projected contents of ulvospinel and ilmenite are increased. These changes are attributed to increased non-ideality along joins from end-member hematite and magnetite to their respective Mg- and Mn-bearing titanate and aluminate end-members. The compositional shifts are most pronounced in Ilm-Hem in the range Ilm_(50-80), a solvus region where the chemical potentials of the hematite and ilmenite components are nearly independent of composition. The solvus gap widens with addition of Mg and even further with Mn. The Bacon-Hirschmann correlation of Mg/Mn in Usp-Mt and coexisting Ilm-Hem is displaced toward increasing Mg/Mn in ilmenite with passage from ordered ilmenite to disordered hematite. Orthopyroxene and biotite crystallized in experiments with added MgO and MgO + MnO; their Z_(Fe) varies with Iog_(10)f_(O_2) and T consistent with equilibria among ferrosilite, annite, and ferrite components, and the chemical potentials of SiO_2 and orthoclase in the liquid. Experimental equilibration rates increased in the order: Opx < Bt < Ilm-Hem < Usp-Mag.
机译：包含TiO_2和氧化铁的合成的低熔点流纹岩组合物，以及进一步单独添加的MgO，MnO和MgO + MnO，被用于水热实验中，以在800和900℃结晶Ilm-Hem和Usp-Mt固溶体在氧化还原条件下，略低于镍-镍氧化物（NNO），比NNO氧气缓冲液高出约= 3 Iog_（10）f_（O_2）单位。这些实验提供了在以前的平衡实验难以涵盖的温度和氧气逸度条件下对FeTi氧化物温度计+氧气气压计的校准。在Roozeboom图表中，我们的数据的等温线表示预期的usp相对于ilm的百分比在ilm为60％时出现了斜率变化，这与从FeTi有序Ilm到FeTi无序Ilm-Hem的二阶过渡一致。系统的此功能可解决与温度计的早期热力学校准不同的部分问题，但并非全部。在含有1.0重量％的MgO的流纹岩中，0.8重量％。含有6％的MnO或MgO + MnO的Usp-Mt结晶有多达14％的铝酸盐组分，而Ilm-Hem结晶了有多达13％的钾钾长石组分和17％的吡phan石组分。相对于FeTiAlO系统，这些成分取代了Usp-Mt中的铁素体成分，取代了Ilm-Hem中的赤铁矿成分。结果，增加了ulvospinel和钛铁矿的含量。这些变化归因于从端部赤铁矿和磁铁矿到其各自的含Mg和Mn的钛酸盐和铝酸盐端部的连接处的非理想性增加。在Ilm-Hem范围Ilm_（50-80）范围内，组成变化最为明显，这是一个固溶区，赤铁矿和钛铁矿组分的化学势几乎与组成无关。固溶间隙随着Mg的添加而加宽，甚至随着Mn的增加而增加。 Usp-Mt中Mg / Mn和共存的Ilm-Hem的Bacon-Hirschmann相关性随着钛铁矿中有序钛铁矿向无序赤铁矿的传递而朝着增加钛铁矿中Mg / Mn的方向移动。在添加了MgO和MgO + MnO的实验中，邻苯二酚和黑云母结晶。它们的Z_（Fe）随Iog_（10）f_（O_2）和T的变化而变化，与铁硅石，铁矿和铁素体组分之间的平衡以及液体中SiO_2和原铝酸钾的化学势一致。实验平衡速率按以下顺序增加：Opx

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