The viscosity of ilmenite is an important parameter that is thought to have influenced the thermal and chemical evolution of the lunar cumulate mantle. We conduct deformation experiments on two different ilmenite compositions, ilmenite100 (FeTiO₃) and ilmenite40 ((Fe_0.4Mg_0.6)TiO₃), to investigate the influence of pressure and Mg‐content on the rheology of ilmenite aggregates. Experiments were conducted in a Griggs apparatus and a deformation‐DIA apparatus at pressures spanning 1–5 GPa. Using the new experimental data and reanalyzed data from Dygert et al. (2016), we determine pressure‐dependent flow law parameters for ilmenite100 (A = 2.183 MPa⁻ⁿs⁻¹, n = 3.0 ± 0.4, E = 276 ± 25 kJ/mol and V = 17 ± 4 cm³/mol) and ilmenite40 (A = 3.936e−7 MPa⁻ⁿs⁻¹, n = 5.7 ± 0.5, E = 283 ± 25 kJ/mol and V = 26 ± 4 cm³/mol). Over the range of experimental conditions ilmenite40 has a larger stress exponent and activation volume than ilmenite100. Extrapolation of the ilmenite100 flow law predicts a viscosity approximately five orders of magnitude lower than dry olivine and three orders of magnitude lower than wet olivine at a temperature of 1,100°C, pressure of 0.3 GPa, and stress of 0.3 MPa, conditions representative of the early ilmenite‐bearing cumulate. Our estimated viscosity contrasts for a dry lunar mantle suggests that lunar cumulate mantle overturn may be dominated by longer wavelength downwellings, while a wet lunar mantle may be dominated by shorter wavelength downwellings.

中文翻译：

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压力和镁含量对钛铁矿流变学的影响：对月球累积地幔倾覆的影响

钛铁矿的粘度是一个重要的参数，被认为已经影响了月积斗的热化学演化。我们对两种不同的钛铁矿成分，钛铁矿100（FeTiO ₃）和钛铁矿40（（Fe _0.4 Mg _0.6）TiO ₃）进行变形实验，以研究压力和镁含量对钛铁矿聚集体流变学的影响。实验是在Griggs仪器和变形DIA仪器中进行的，压力范围为1-5 GPa。使用新的实验数据和Dygert等人的重新分析数据。（2016年），我们确定了钛铁矿100的压力相关流动规律参数（A  = 2.183 MPa ^-n s ^-1，n  = 3.0±0.4，E  = 276±25 kJ / mol和V  = 17±4 cm ³ / mol）和钛铁矿40（A  = 3.936e-7 MPa ^-n s ^-1，n  = 5.7±0.5，E  = 283 ±25 kJ / mol且V  = 26±4 cm ³/ mol）。在实验条件范围内，钛铁矿40比钛铁矿100具有更大的应力指数和活化体积。钛铁矿100流动规律的外推法预测在温度为1100°C，压力为0.3 GPa，应力为0.3 MPa的条件下，粘度比干橄榄石低大约五个数量级，比湿橄榄石低三个数量级。早期含钛铁矿累积。我们针对干燥月球地幔的估计粘度对比表明，较长的波长下涌可能是月球累积地幔倾覆的主要因素，而较短的波长下涌可能是占月球湿地幔的主要因素。