Volcanic products returned from the Apollo missions over 50 years ago provide a unique perspective into the magmatic evolution of the Moon. However, questionsremain regarding the volatile loss, crystallization, and emplacement histories of lunar lavas. To address gaps in our understanding of the eruptive histories of lunar lavas, we investigate phase chemistry and 3D morphologies of low-titanium Apollo 15 basalts belonging to the olivine-normative and quartz-normative suites. We report the 2D and 3D petrography, mineral chemistry, and 3D void space morphologies of 15499, 15555, 15556, and the lesser studied 15495 and 15608 basalts. Quantitative apatite chemistry shows a wide range of apatite volatile compositions and that low-Ti basalt 15495 may contain the most OH-rich compositions measured from the Moon. Analyses of metal grains within the low-Ti basalts have expanded the field of expected Ni and Co metal concentrations for Apollo 15 mare basalts and are used to determine the petrogenesis of two of the studied samples. Coupling 2D chemistry with nondestructive 3D morphologic analyses provides critical insights on the relative timing of volatile exsolution in low-titanium lavas. Through the analysis of vesicles and vugs from X-ray computed tomographic data, we report the first 3D void space volume percentages for a suite of low-Ti basalts and show that these basalts degassed before the onset of mesostasis (e.g., apatite) crystallization. We use calculated cooling rates and 3D morphologic analyses to show that the studied basalts crystallized at various depths in separate lava flows, and 15608 represents the quenched margin of a mare flow. Our work highlights the value of combining 2D and 3D analytical techniques to study the emplacement history of basalts that lack geological context.

中文翻译：

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通过 2D 和 3D 研究评估低钛玄武岩的结晶和喷发历史


50 多年前从阿波罗任务中返回的火山产物为了解月球的岩浆演变提供了独特的视角。然而，关于月球熔岩的挥发性损失、结晶和放置历史仍然存在疑问。为了解决我们对月球熔岩喷发历史的理解差距，我们研究了属于橄榄石-标准和石英-标准套件的低钛阿波罗 15 号玄武岩的相化学和 3D 形态。我们报道了 15499、15555、15556 以及研究较少的 15495 和 15608 玄武岩的 2D 和 3D 岩石学、矿物化学和 3D 空隙空间形态。定量磷灰石化学显示磷灰石挥发性成分范围很广，低钛玄武岩 15495 可能含有从月球测得的最具氢含量的成分。对低钛玄武岩中金属晶粒的分析扩大了阿波罗 15 号母马玄武岩的预期镍和钴金属浓度范围，并用于确定其中两个研究样品的岩石成因。将 2D 化学与无损 3D 形态学分析相结合，可以深入了解低钛熔岩中挥发性物质溶出的相对时间。通过分析 X 射线计算机断层扫描数据中的囊泡和孔洞，我们报告了一组低 Ti 玄武岩的第一个 3D 空隙空间体积百分比，并表明这些玄武岩在介态（例如磷灰石）结晶开始之前脱气。我们使用计算的冷却速率和 3D 形态学分析来表明，所研究的玄武岩在不同深度以单独的熔岩流结晶，15608 代表母马流的淬火边缘。 我们的工作强调了结合 2D 和 3D 分析技术来研究缺乏地质背景的玄武岩的放置历史的价值。