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Modeling Lunar Pyroclasts to Probe the Volatile Content of the Lunar Interior
Journal of Geophysical Research: Planets ( IF 4.8 ) Pub Date : 2021-03-29 , DOI: 10.1029/2020je006645
Darien Florez 1 , Christian Huber 1 , Ralph E. Milliken 1 , Julia Berkson 1
Affiliation  

Constraining the volatile budget of the lunar interior has important ramifications for models of Moon formation. While many early and previous measurements of samples acquired from the Luna and Apollo missions suggested the lunar interior is depleted in highly volatile elements like H, a number of high‐precision analytical studies over the past decade have argued that it may be more enriched in water than previously thought. Here, we integrate recent remotely sensed near‐infrared reflectance measurements of small Dark‐Mantle‐Deposits (DMDs) Birt E and Grimaldi, interpreted to represent pyroclastic deposits, and physics‐based eruption models to better constrain the preeruptive water content of the magmas that resulted in these deposits. We model the trajectory and water loss of pyroclasts from eruption to deposition, coupling eruption dynamics with a volatile diffusion model for each pyroclast. Modeled pyroclast sizes and final water contents are then used to predict spectral reflectance properties for comparison with the observed orbital near‐infrared data. We develop an inversion scheme based on the Markov‐Chain Monte‐Carlo (MCMC) method to retrieve constraints between governing parameters such as the initial volatile content of the melt and the pyroclast size distribution (which influences the remotely measured water absorption strengths). The MCMC inversion allows us to estimate the primordial (preeruption) water content for different DMDs and therefore explore whether their source is volatile‐rich. Our results suggest that the preeruptive water content of the magmas sampled by Birt E and Grimaldi can be constrained within a range 400–800 ppm, while the pyroclast size in diameter corresponding to the 50th percentile of a given deposit likely ranges from ∼400 to 600 μm in diameter. Finally, we determine the evaporation and cooling rates are likely low, ∼10−6 m/s and 6°C/s, respectively.

中文翻译:

建模月历爆破岩以探究月球内部的挥发性物质

限制月球内部波动的预算对于月球形成模型具有重要的影响。虽然从Luna和Apollo任务中获得的许多早期和先前的样品测量结果都表明,月球内部的H等高挥发性元素已被消耗,尽,但在过去十年中,许多高精度分析研究都认为它可能更富于水。比以前想像的要多。在这里,我们将最近的小暗幔沉积(DMD)Birt E和Grimaldi的遥感近红外反射测量结果结合起来,解释为代表火山碎屑沉积,并结合了基于物理的喷发模型,以更好地限制岩浆的喷发前含水量。导致这些存款。我们模拟了火山爆发从喷发到沉积的轨迹和水分流失,将火山爆发动力学与每个火山碎屑的挥发性扩散模型耦合。然后使用模型化的火山碎屑大小和最终水含量预测光谱反射率特性,以便与观测到的轨道近红外数据进行比较。我们基于Markov-Chain Monte-Carlo(MCMC)方法开发了一种反演方案,以检索控制参数之间的约束条件,例如熔体的初始挥发物含量和破火山体尺寸分布(这会影响远程测量的吸水强度)。MCMC反演使我们能够估计不同DMD的原始(喷发)水含量,从而探究其来源是否富含挥发性物质。我们的结果表明,由Birt E和Grimaldi采样的岩浆的喷发前水含量可以限制在400-800 ppm范围内,而对应于给定沉积物的第50个百分位的破火山体的直径大小可能在直径约400至600μm的范围内。最后,我们确定蒸发和冷却速率可能较低,约为10-6  m / s和6°C / s。
更新日期:2021-04-13
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