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Geothermometry using minor and trace elements in igneous and hydrothermal magnetite
Chemical Geology ( IF 3.6 ) Pub Date : 2020-05-01 , DOI: 10.1016/j.chemgeo.2020.119576
Dante Canil , Terri Lacourse

Abstract The temperature (T) and oxygen fugacity (fO2) dependence of minor and trace elements (Mg, Al, Mn, Cr, Ni) in magnetite (Mag) in equilibrium with water-bearing silicate liquids varying in composition from basalt to rhyolite (49–77 wt% SiO2) is examined in a compilation of experimental data (n = 299) from 700 to 1050 °C, 50–900 MPa and five order of magnitude range in fO2. The XMg (=Mg/(Mg + Fetot)) of Mag is strongly dependent on T, and can be formulated into an empirical geothermometer: TMg−mag (°C) = − 8344(±320)/[lnXMg − 4.1(±0.28)] – 273 r2 = 0.83 that reproduces 72% of the experimentas to ±50 °C, and conventional Fe Ti oxide thermometry in tuffs and vitrophyres to better than ±60 °C for >85% of the samples. The TMg Mag thermometer may have potential application in igneous or hydrothermally altered rocks where conventional thermometry or oxybarometry is not possible. Application to natural Mag (n = 476) compiled from several settings shows igneous rocks mostly record >700 °C but with some lower temperatures in plutonic rocks due to slow cooling. Hydrothermal samples (skarns, porphyry deposits) show consistently subsolidus conditions (TMg-mag of 700–350 °C) consistent with other mineral and O isotopic equilibria. The element correlations in natural Mag from various settings are explored using multivariate statistical analysis, to identify which minor or trace elements most critically depend on T, fO2 or fluid composition.

中文翻译:

使用火成岩和热液磁铁矿中的微量元素和微量元素进行地热测量

摘要 磁铁矿 (Mag) 中微量和微量元素 (Mg、Al、Mn、Cr、Ni) 与温度 (T) 和氧逸度 (fO2) 的相关性与组成从玄武岩到流纹岩的含水硅酸盐液体平衡( 49–77 wt% SiO2) 在 700 到 1050 °C、50–900 MPa 和 fO2 的五个数量级范围内的实验数据 (n = 299) 的汇编中进行了检查。Mag 的 XMg (=Mg/(Mg + Fetot)) 与 T 密切相关,可以公式化为经验地温计: TMg−mag (°C) = − 8344(±320)/[lnXMg − 4.1(± 0.28)] – 273 r2 = 0.83 可将 72% 的实验重现至 ±50 °C,并且对于 > 85% 的样品,凝灰岩和玻璃岩中的常规 Fe Ti 氧化物温度测量优于 ±60 °C。TMg Mag 温度计可能在火成岩或热液蚀变岩石中具有潜在的应用,在这些岩石中,传统的温度测量法或氧气压法是不可能的。应用到自然 Mag (n = 476) 从几个设置编译显示火成岩大多记录 >700 °C,但由于缓慢冷却,深成岩的温度较低。热液样品(矽卡岩、斑岩矿床)显示出与其他矿物和 O 同位素平衡一致的亚固相线条件(TMg-mag 700-350 °C)。使用多元统计分析来探索来自各种环境的自然 Mag 中的元素相关性,以确定哪些微量或痕量元素最关键地取决于 T、fO2 或流体成分。应用到自然 Mag (n = 476) 从几个设置编译显示火成岩大多记录 >700 °C,但由于缓慢冷却,深成岩的温度较低。热液样品(矽卡岩、斑岩矿床)显示出与其他矿物和 O 同位素平衡一致的亚固相线条件(TMg-mag 700-350 °C)。使用多元统计分析来探索来自各种环境的天然 Mag 中的元素相关性,以确定哪些微量元素或痕量元素最关键地取决于 T、fO2 或流体成分。应用到自然 Mag (n = 476) 从几个设置编译显示火成岩大多记录 >700 °C,但由于缓慢冷却,深成岩的温度较低。热液样品(矽卡岩、斑岩矿床)显示出与其他矿物和 O 同位素平衡一致的亚固相线条件(TMg-mag 700-350 °C)。使用多元统计分析来探索来自各种环境的天然 Mag 中的元素相关性,以确定哪些微量元素或痕量元素最关键地取决于 T、fO2 或流体成分。
更新日期:2020-05-01
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