On the eruptive origins of lunar localized pyroclastic deposits
On the eruptive origins of lunar localized pyroclastic deposits
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月球局部火山碎屑沉积物的喷发起源
DOI：
10.1016/j.epsl.2020.116426
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发表时间：
2020
影响因子：
5.3
通讯作者：
Robinson, Mark S.
中科院分区：
文献类型：
--
作者：
Keske, Amber L.;Clarke, Amanda B.;Robinson, Mark S.
局部火山碎屑沉积物（LPD）是火山碎屑物质的低反照率堆积物，具有明显的正地形特征，主要沿高地-海马边界发现。先前的研究人员假设LPD代表了相当于月球火山喷发的产物，部分基于观察到阿方索斯陨石坑的一些沉积物与其沉积物体积相比具有较大的喷口体积，这表明沉积物中幼年物质的比例较低。这项研究的目的是通过使用当代数据和方法确定阿方索斯陨石坑和月球其他地方的 LPD 中幼年物质的比例（根据沉积物和喷口体积计算得出）如何变化，从而更好地了解喷发机制。来自 11 个地点的 23 个 LPD 的沉积量和喷发量是通过使用源自月球勘测轨道器相机窄角相机 (LROC NAC) 的数字地形模型 (DTM) 对当前和模拟的喷发前表面进行差异计算得出的。结果表明，LPD 的幼体比例范围很广，其中许多幼体的数量比之前想象的要多。此外，幼体物质比例与沉积体积和厚度之间存在正相关关系，幼体体积与扩散面积之间也存在正相关关系。 LPD 还具有广泛的变薄剖面，涵盖地球上多种喷发类型。这些发现以及之前对这些矿床进行光谱分析的研究表明，LPD在成分和形态测量方面存在比以前理解的更大的多样性，并且之前发表的简化的瓦肯模型可能仅适用于含有最少量幼年物质的矿床，而所有其他矿床可能需要多种喷发机制的组合。此外，动态模型结果表明，本研究中最广泛的月球沉积物是由含有 2000-5000 ppm 溶解挥发物的岩浆形成的，这与最近通过熔体包裹体分析的估计一致，但与长期以来认为月球在形成过程中很大程度上脱气的观点相反。
Localized pyroclastic deposits (LPDs) are low-albedo accumulates of pyroclastic material with distinct positive topographic signatures that are found dominantly along highland-mare boundaries. Previous workers hypothesized that LPDs represent products of a lunar equivalent of Vulcanian-style eruptions, based in part on the observation that some of the deposits in Alphonsus Crater have large vent volumes in comparison with their deposit volumes, indicating a low proportion of juvenile material in the deposits. The objective of this study is to better understand eruption mechanisms by determining how the proportion of juvenile material, as calculated using deposit and vent volumes, varies among LPDs in Alphonsus Crater and elsewhere on the Moon using contemporary data and methods. Deposit and vent volumes for 23 LPDs from eleven sites were calculated by differencing current and modeled pre-eruption surfaces using digital terrain models (DTMs) derived from Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC). Results show that LPDs have a wide range of juvenile proportions, many of which are more juvenile-rich than previously thought. Additionally, there is a positive relationship between juvenile material proportion and deposit volume and thickness, and a positive relationship between juvenile volume and dispersal area. LPDs also bear a broad range of thinning profiles which span a range of multiple eruption types on Earth. These findings, along with previous studies employing spectroscopic analysis of these deposits, indicate there is greater diversity among LPDs in composition and morphometry than previously understood, and that previously published simplified Vulcanian models may apply only to the deposits containing the least amount of juvenile material, with all others perhaps requiring a combination of multiple eruptive mechanisms. Furthermore, dynamic model results suggest that the most widespread lunar deposits in this study were formed by magma containing 2000–5000 ppm of dissolved volatiles, consistent with recent estimates via melt inclusion analysis, but contrary to long-held ideas that the Moon was largely degassed during its formation.
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