Abstract 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.

中文翻译：

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月球局部火山碎屑沉积物的喷发成因

摘要 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-海边界发现。以前的工作人员假设 LPD 代表了相当于月球火山式火山喷发的产物，部分是基于观察到，Alphonsus Crater 中的一些沉积物与其沉积物体积相比具有较大的喷口体积，这表明其中的幼年物质比例较低。存款。本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上其他地方的 LPD 之间的幼年物质比例如何变化，从而更好地了解喷发机制，使用沉积物和喷口体积计算。来自 11 个地点的 23 个 LPD 的沉积和通风量是通过使用源自月球勘测轨道飞行器相机窄角相机 (LROC NAC) 的数字地形模型 (DTM) 对当前和模拟的喷发前表面进行区分来计算的。结果表明，LPD 的少年比例范围很广，其中许多比以前认为的更丰富。此外，幼体材料比例与沉积量和厚度之间存在正相关关系，幼体体积与分散面积之间存在正相关关系。LPD 还具有广泛的变薄剖面，涵盖地球上的多种火山喷发类型。这些发现，以及之前对这些沉积物进行光谱分析的研究，表明 LPD 在成分和形态测量方面的多样性比以前理解的要大，而且以前公布的简化 Vulcanian 模型可能仅适用于含有最少量幼年物质的沉积物，而所有其他模型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得出的估计值一致，但与长期以来认为月球大部分脱气的观点相反在其形成过程中。与所有其他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得出的估计值一致，但与长期以来认为月球大部分脱气的观点相反在其形成过程中。与所有其他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得出的估计值一致，但与长期以来认为月球大部分脱气的观点相反在其形成过程中。