Volcanic products returned from the Apollo missions over 50 years ago provide a unique perspective into the magmatic evolution of the Moon. However, questions remain 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.

Despite being essentially water-free, nominally anhydrous minerals such as plagioclase and pyroxene represent the biggest reservoir of water in most lunar rocks due to their sheer abundance. Apatite, which incorporates F, Cl, and OH into its mineral structure as essential crystal components, on the other hand, is the only other volatile-bearing phase common in lunar samples. Here, we present the first coordinated study of volatiles (e.g., H2O, Cl, F, and S) in nominally anhydrous minerals combined with isotopic measurements in apatite from the ancient lunar basalt fragments from meteorite Miller Range (MIL) 13317. Apatite in MIL 13317 basalt contains similar to 2000 ppm H2O and has an elevated SD values (+ 523-737 parts per thousand), similar to Apollo mare basalts, but has high delta Cl-37 values (+ 29-36 parts per thousand), similar to apatite found in several KREEP-rich samples. MIL 13317 is unique compared with other lunar basalts; it has both elevated SD and delta Cl-37 values currently only observed in highlands sample 79215 (a granulitic impactite). Based on measurements of H2O in nominally anhydrous minerals and in apatite, the source magma of MIL 13317 basalt is estimated to contain similar to 130-330 ppm H2O. Assuming reasonable levels of partial melting of the lunar mantle and magmatic degassing during eruption of the basalt, the Moon contained at least one reservoir with < 100 ppm H2O, a delta D value of < 0 parts per thousand similar to carbonaceous chondrites, and extensively fractionated Cl isotopes prior to 4.332 Gyr, the crystallization age of the MIL 13317 basalt.

The Moon is generally depleted in volatile elements and this depletion extends to the surface where the most abundant mineral, anorthite, features <6 ppm H2O. Presumably the other nominally anhydrous minerals that dominate the mineral composition of the global surface-olivine and pyroxene-are similarly depleted in water and other volatiles. Thus the Moon is tabula rasa for the study of volatiles introduced in the wake of its origin. Since the formation of the last major basin (Orientale), volatiles from the solar wind, from impactors of all sizes, and from volatiles expelled from the interior during volcanic eruptions have all interacted with the lunar surface, leaving a volatile record that can be used to understand the processes that enable processing, transport, sequestration, and loss of volatiles from the lunar system. Recent discoveries have shown the lunar system to be complex, featuring emerging recognition of chemistry unanticipated from the Apollo era, confounding issues regarding transport of volatiles to the lunar poles, the role of the lunar regolith as a sink for volatiles, and the potential for active volatile dynamics in the polar cold traps. While much has been learned since the overturn of the Moon is dry paradigm by innovative sample and spacecraft measurements, the data point to a more complex lunar volatile environment than is currently perceived.

The Tacquet Formation (TF) was first identified in geologic mapping of southern Mare Serenitatis as a distinct low albedo region split by the linear Rimae Menelaus rilles. A distinct western dome, split by a linear rille and less distinct eastern dome (the Menelaus domes) are also present within the TF. Previous Earth-based radar analyses showed that the TF has a lower circular polarization ratio consistent with a pyroclastic mantle. In this study, compositional and spectroscopic parameters were derived from Moon Mineralogy Mapper (M-3) data. Lunar Reconnaissance Orbiter Camera Wide Angle Camera (LROC WAC) and SELENE Kaguya Multiband Imager (MI) multispectral data were also utilized. FeO derived from MI data for the TF and Menelaus domes was elevated at levels consistent with pyroclastic glasses. While not diagnostic of pyroclastics, TiO2 derived from LROC WAC data over the TF and Menelaus domes was also elevated relative to the background materials. Analysis of 1 and 2 mu m band parameters also show the TF and Menelaus domes as being distinct with a band center moderately longer than 1 mu m and 2 mu m band center shorter than the surroundings, characteristics consistent with pyroclastic glass and/or increased ilmenite. M-3 data thermally corrected via two different thermal correction approaches indicate a moderately deeper band in the 3 mu m region indicative of OH and/or H2O, a characteristic that is also potentially associated with pyroclastic deposits. These compositional findings are consistent with the Earth-based radar data suggesting that the TF is a pyroclastic mantle and potentially represents a previously unrecognized sub-class of pyroclastic deposits associated with lunar volcanic domes.

A transient lunar atmosphere formed during a peak period of volcanic outgassing and lasting up to about similar to 70 Ma was recently proposed. We utilize forward-modeling of individual lunar basaltic eruptions and the observed geologic record to predict eruption frequency, magma volumes, and rates of volcanic volatile release. Typical lunar mare basalt eruptions have volumes of similar to 10(2)-10(3) km(3), last less than a year, and have a rapidly decreasing volatile release rate. The total volume of lunar mare basalts erupted is small, and the repose period between individual eruptions is predicted to range from 20,000 to 60,000 years. Only under very exceptional circumstances could sufficient volatiles be released in a single eruption to create a transient atmosphere with a pressure as large as similar to 0.5 Pa. The frequency of eruptions was likely too low to sustain any such atmosphere for more than a few thousand years. Transient, volcanically induced atmospheres were probably inefficient sources for volatile delivery to permanently shadowed lunar polar regions.

Volatile-bearing lunar surface and interior, giant magmatic-intrusion-laden near and far side, globally distributed layer of purest anorthosite (PAN) and discovery of Mg-Spinel anorthosite, a new rock type, represent just a sample of the brand new perspectives gained in lunar science in the last decade. An armada of missions sent by multiple nations and sophisticated analyses of the precious lunar samples have led to rapid evolution in the understanding of the Moon, leading to major new findings, including evidence for water in the lunar interior. Fundamental insights have been obtained about impact cratering, the crystallization of the lunar magma ocean and conditions during the origin of the Moon. The implications of this understanding go beyond the Moon and are therefore of key importance in solar system science. These new views of the Moon have challenged the previous understanding in multiple ways and are setting a new paradigm for lunar exploration in the coming decade both for science and resource exploration. Missions from India, China, Japan, South Korea, Russia and several private ventures promise continued exploration of the Moon in the coming years, which will further enrich the understanding of our closest neighbor. The Moon remains a key scientific destination, an active testbed for in-situ resource utilization (ISRU) activities, an outpost to study the universe and a future spaceport for supporting planetary missions.