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.

Lunar volcanic volatiles are crucial for understanding eruption dynamics on the Moon as well as the potential formation, life span, and dissipation of a lunar secondary atmosphere. We review literature concerning volatile content, degassing extent, and speciation during the mare eruption period on the Moon from 4.0 to 1.2 Ga, providing a realistic summary of degassed compositions for the traditional volcanic elements C-O-H-S-F-Cl. The most reliable estimates of lunar volcanic volatiles come from high-titanium (high-Ti) glass beads sampled during the Apollo 17 mission. Analysis of these samples demonstrates that hydrogen is the most abundant element by mole in erupted volcanic gases, so a hydrogen species should be the most abundant molecule in the lunar gas, rather than carbon monoxide. This hydrogen is expected to speciate mostly as H2, rather than H2O, at the predicted oxygen fugacity for lunar magma. This difference is important because H2 more easily escapes from the Moon, whereas H2O could freeze out on the lunar surface, and potentially persist within permanently shadowed regions near the poles. We also find that sulfur, rather than carbon, is the third most abundant element in lunar volcanic gas, after hydrogen and oxygen.

Core-mantle friction induced by the precession of the Moon's spin axis is a strong heat source in the deep lunar mantle during the early phase of a satellite's evolution, but its influence on the long-term thermal evolution still remains poorly explored. Using a one-dimensional thermal evolution model, we show that core-mantle friction can sustain global-scale partial melting in the upper lunar mantle until similar to 3.1 Ga, thus accounting for the intense volcanic activity on the Moon before similar to 3.0 Ga. Besides, core-mantle friction tends to suppress the secular cooling of the lunar core and is unlikely to be an energy source for the long-lived lunar core dynamo. Our model also favours the transition of the Cassini state before the end of the lunar magma ocean phase (similar to 4.2 Ga), which implies a decreasing lunar obliquity over time after the solidification of the lunar magma ocean. Such a trend of lunar obliquity evolution may allow volcanically released water to be buried in the lunar regolith of the polar regions. As a consequence, local water ice could be more abundant than previously thought when considering only its accumulation caused by solar wind and comet spreading. Precession-driven core-mantle friction can maintain a long-lived volcanism on the Moon until similar to 3.1 Ga. Modelling suggests the Cassini state transition before the end of lunar magma ocean phase (similar to 4.2 Ga), which allows a decreasing lunar obliquity over time and the deposition of water ice in the lunar polar regions afterwards.

Lunar Pyroclastic Deposits (LPDs) are sites of explosive volcanism and often occur in areas of effusive volcanism on the Moon. On Earth, it has been observed that most volcanism has both effusive and explosive phases, whereas on the Moon, these two types of volcanism have typically been considered separately. We hypothesize that the relationship between explosive and effusive volcanism on the Moon is similar to what is observed on the Earth, where individual eruptions can experience multiple phases rather than one type of volcanism always preceding another or occurring separately. We present observations from the Moon Mineralogy Mapper detailing compositional relationships between volcanic features in the lunar Montes Apenninus region. We evaluated whether co-located LPDs and effusive features (e.g., rilles, mare) could have erupted from the same volcanic vent or even at the same time based on their compositional similarities and stratigraphic relationships. We found that the LPDs have varied stratigraphic relationships with co-located effusive features. We identified LPDs near sinuous rilles that may be related to the formation of the rille, where explosive and effusive volcanism occurred at the same vent (e.g., Mozart Rille), and LPDs that may be unrelated to the rille (e.g., Rimae Bode and Rima Bode LPD). Our results suggest that lunar volcanism can mirror terrestrial volcanism, with explosive and effusive eruptions demonstrating more complex dynamics and relationships than previously thought. This variability suggests that the relationship between LPDs and nearby volcanic features cannot be generalized for studies on their resource potential, eruption styles, or deposit volume.

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.

Explosive volcanic eruptions are responsible for producing localized pyroclatic deposits found across the lunar surface. These small localized pyroclastic deposits are thought to have erupted through transient, vulcanian-like eruptions. We used several remote data products, including a water abundance map, to understand the compositional and physical properties of these pyroclastic deposits. Within these deposits, we found strong relationships between water abundance and pyroxene abundance, glass abundance, regolith density scale height, and longitude. These relationships suggest that water abundance can be used to estimate the gas content of an eruption, cooling rate of erupted pyroclasts, optical density of the eruption plume, degree of fragmentation of an eruption, and infer on the distribution of water in the lunar interior. Further, we deduce that the excess water abundance within these pyroclastic deposits represents interior water content, which we tied to other remote measurements that represent important petrological and volcanological parameters to understand eruption dynamics and behavior.

The Early 20th Century Warming (ETCW) in the northern high latitudes was comparable in magnitude to the present-day warming yet occurred at a time when the growth in atmospheric greenhouse gases was rising significantly less than in the last 40 years. The causes of ETCW remain a matter of debate. The key issue is to assess the contribution of internal variability and external natural and human impacts to this climate anomaly. This paper provides an overview of plausible mechanisms related to the early warming period that involve different factors of internal climate variability and external forcing. Based on the vast variety of related studies, it is difficult to attribute ETCW in the Arctic to any of major internal variability mechanisms or external forcings alone. Most likely it was caused by a combined effect of long-term natural climate variations in the North Atlantic and North Pacific with a contribution of the natural radiative forcing related to the reduced volcanic activity and variations of solar activity as well as growing greenhouse gases concentration in the atmosphere due to anthropogenic emissions.

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 similar to 400 to 600 mu m in diameter. Finally, we determine the evaporation and cooling rates are likely low, similar to 10(-6) m/s and 6 degrees C/s, respectively.