Long Xiao

A young multilayered terrane of the northern Mare Imbrium revealed by Chang’E-3 mission

Onsite radar shows what lies beneath In more active periods of the Moons history, volcanic eruptions created lava plains that formed layers of dark basalt. Without subsurface probing, we can only examine the most recent flows. After the soft landing of the ChangE-3 spacecraft, Xiao et al. made penetrating radar measurements of the lunar crust with the Yutu rover. Several subsurface layers suggest multiple geologic processes at play throughout the crustal history, including multiple lava flows and the weathering-induced creation of dust and rocky debris. Science, this issue p. 1226 In situ ground-penetrating radar measurements of the lunar crust reveal multiple layers of regolith and lava flows. China’s Chang’E-3 (CE-3) spacecraft touched down on the northern Mare Imbrium of the lunar nearside (340.49°E, 44.12°N), a region not directly sampled before. We report preliminary results with data from the CE-3 lander descent camera and from the Yutu rover’s camera and penetrating radar. After the landing at a young 450-meter crater rim, the Yutu rover drove 114 meters on the ejecta blanket and photographed the rough surface and the excavated boulders. The boulder contains a substantial amount of crystals, which are most likely plagioclase and/or other mafic silicate mineral aggregates similar to terrestrial dolerite. The Lunar Penetrating Radar detection and integrated geological interpretation have identified more than nine subsurface layers, suggesting that this region has experienced complex geological processes since the Imbrian and is compositionally distinct from the Apollo and Luna landing sites.

Cooling fractures in impact melt deposits on the Moon and Mercury: Implications for cooling solely by thermal radiation

We study the distribution, morphology, and geometrical properties of fractures in several young impact melt deposits on the Moon and Mercury, and the ways that these fractures may form from cooling by thermal radiation. In each impact melt complex, the topography of the underlying terrain determines the orientation of cooling fractures, such that interior fractures that formed in the relatively thick interior areas of the melt unit are wider and have a larger spacing than marginal fractures that formed in the relatively thin areas near the units margins. Solid debris entrained in molten deposits provides prefracture flaws that can seed cooling fractures, but too much solid debris prevents cooling fractures from growing to macroscopic sizes. The appearance of subparallel fractures is mainly caused by subsidence of the deposits during the process of cooling and solidification. Tensile stresses caused by thermal radiation are large enough to initiate cooling fractures on both the Moon and Mercury, which may represent the initial stage of columnar joints formation, but the cooling rate caused solely by thermal radiation is not large enough to form well-organized columnar joints that feature polygonal colonnades. We therefore propose that thermal conduction and convection are the major contributors in the formation of columnar joints on planetary bodies.

U-Pb geochronology of detrital and inherited zircons in the Yidun arc belt, eastern Tibet Plateau and its tectonic implications

This paper reports geochronological data of detrital zircons from the country rock and sedimentary xenoliths of the Cilincuo pluton (79±0.7 Ma) in the southern Yidun arc belt and the inherited zircons from the Late Triassic granites in the eastern Yidun arc belt, eastern Tibet Plateau. Detrital zircons ages from the sedimentary xenoliths have four prominent peaks at 2.5–2.4 Ga, 1.9–1.8 Ga, 480–400 Ma, and 350–300 Ma, whereas those from the country rock exhibit another four prominent peaks at 1.9–1.8 Ga, 850–700 Ma, 480–400 Ma, and 300–250 Ma. Based on comparison with age data from previous studies, we suggest that the sedimentary xenoliths are from the Lanashan Formation and the major provenance of them is Qiangtang Block, Zhongza massif and South China Block, whereas the country rock belongs to the Lamaya Formation and the major provenance of them is similar to those of the neighbouring Songpan-Garzê terrane. In addition, the inherited zircons from the Late Triassic granites in the eastern Yidun arc belts have a prominent Neoproterozoic age population (900–700 Ma), which suggests that there is an old basement with west Yangtze Craton affinity beneath the Triassic sediments. Combining with previous studies, we propose that the provenances of the formations vary from the Lanashan Formation to the Lamaya Formation which may indicate a record of the final closure of the Garzê-Litang Ocean.

Ina pit crater on the Moon: Extrusion of waning-stage lava lake magmatic foam results in extremely young crater retention ages

The enigmatic Ina feature on the Moon was recently interpreted to represent extrusive basaltic volcanic activity within the past 100 m.y. of lunar history, an extremely young age for volcanism on the Moon. Ina is a 2 × 3 km D-shaped depression that consists of a host of unusual bleb-like mounds surrounded by a relatively optically fresh hummocky and blocky floor. Documentation of magmatic-volcanic processes from shield volcano summit pit craters in Hawai’i and new insights into shield-building and dike evolution processes on the Moon provide important perspectives on the origin of Ina. We show that the size, location, morphology, topography, and optical maturity of Ina are consistent with an origin as a subsided summit pit crater lava lake on top of a broad ~22-km-diameter, ~3.5-b.y.-old shield volcano. New theoretical treatments of lunar shield-building magmatic dike events predict that waning-stage summit activity was characterized by the production of magmatic foam in the dike and lake; the final stages of dike stress relaxation and closure cause the magmatic foam to extrude to the surface through cracks in the lava lake crust to produce the mounds. The high porosity of the extruded foams (>75%) altered the nature of subsequent impact craters (the aerogel effect), causing them to be significantly smaller in diameter, which could bias the crater-derived model ages. Accounting for this effect allows for significantly older model ages, to ~3.5 b.y., contemporaneous with the underlying shield volcano. Thus extremely young volcanic eruptions are not required to explain the unusual nature of Ina.

Chicxulub and the Exploration of Large Peak-Ring Impact Craters through Scientific Drilling

The Chicxulub crater is the only well-preserved peak-ring crater on Earth and linked, famously, to the K-T or K-Pg mass extinction event. For the first time, geologists have drilled into the peak ring of that crater in the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP-ICDP) Expedition 364. The Chicxulub impact event, the environmental calamity it produced, and the paleobiological consequences are among the most captivating topics being discussed in the geologic community. Here we focus attention on the geological processes that shaped the ~200-km-wide impact crater responsible for that discussion and the expedition’s first year results.

The Mons Rümker volcanic complex of the Moon: A candidate landing site for the Chang'E‐5 mission

Mons Rumker is a large volcanic complex in Oceanus Procellarum on the Moon and is a candidate landing site for Chinas ChangE-5 sample return mission. We conducted a comprehensive study of the topography, geomorphology, composition, and stratigraphy of the Mons Rumker region with multi-source remote sensing data in order to better understand the geology of the region and provide further support for the ChangE-5 mission. The results show that the Rumker plateau stands 200–1300 m above the surrounding mare surface and 75% of the plateau has a slope of less than 3° at a baseline length of 30 m. Domes are the most prominent volcanic landforms in Mons Rumker and a total of 22 domes were identified and divided into two types that may represent different stages of volcanic activity. Spectral analyses indicated that Mons Rumker is covered by low-Ti basalt and the dominant mafic mineral is high-calcium pyroxene, though signs of mixing of highland materials and basalt have been found. Mons Rumker has three main basalt units and their absolute model ages are 3.71 Ga, 3.58 Ga and 3.51 Ga, respectively. Steep-sided domes could be the youngest volcanic features on the plateau with indications that they were active until the Eratosthenian. A new geologic map of the study region was produced and used to interpret and discuss the geologic evolution of the region. Finally, we propose two candidate landing sites for the ChangE-5 mission.

Oxalate formation under the hyperarid conditions of the Atacama desert as a mineral marker to provide clues to the source of organic carbon on Mars

In this study, we report the detection and characterization of the organic minerals weddellite n(CaC2O4 · 2H2O) and whewellite (CaC2O4 · H2O) in the hyperarid, Mars-like conditions of the Salar Grande, nAtacama desert, Chile. Weddellite and whewellite are commonly of biological origin on Earth and have great npotential for preserving records of carbon geochemistry and possible biological activity on Mars if they nare present there. Weddellite and whewellite have been found as secondary minerals occurring inside the nlower detrital unit that fills the Salar Grande basin. The extremely low solubility of most oxalate minerals ninhibits detection of oxalate by ion chromatography (IC). Crystalline oxalates, including weddellite and nwhewellite, were detected by X-ray diffraction (XRD). The association of weddellite with surface biota and its npresence among subsurface detrital materials suggest the potential of a biological origin for Salar Grande nweddellite and whewellite. In this regard, biological activity is uniquely capable of concentrating oxalates nat levels detectable by XRD. The complementary detection of oxalate-bearing phases through IC in the upper nhalite-rich unit suggests the presence of a soluble oxalate phase in the basin that is not detected by XRD. nThe formation, transport, and concentration of oxalate in the Salar Grande may provide a geochemical nanalogue for oxalate-bearing minerals recently suggested to exist on Mars.

Subsurface Structures at the Chang'e-3 Landing Site: Interpretations from Orbital and In-Situ Imagery Data

The Chang’e-3 (CE-3) spacecraft successfully landed on one of the youngest mare surfaces on the Moon in December 2013. The Yutu rover carried by CE-3 was equipped with a radar system that could reveal subsurface structures in unprecedented details, which would facilitate understanding regional and global evolutionary history of the Moon. Based on regional geology, cratering scaling, and morphological study, here we quantify the subsurface structures of the landing site using high-resolution orbital and in-situ imagery data. Three layers of lunar regolith, two layers of basalt units, and one layer of ejecta deposits are recognized at the subsurface of the landing site, and their thicknesses are deduced based on the imagery data. These results could serve as essential references for the on-going interpretation of the CE-3 radar data. The ability to validate our theoretical subsurface structure using CE-3 in-situ radar observations will improve the methods for quantifying lunar subsurface structure using crater morphologies and scaling.

Geological features and magmatic activities history of sinus Iridum, the moon

The Sinus Iridum region is one of the most important candidate landing targets for Chinese lunar landing mission ChangE-3 (CE-3). Because of its flat topography, complex evolution history and abundance of geological features, it shows great significance to both science and engineering. There are abundant geological features, such as winkle ridges, mare rilles, impact craters and crater chains in this region, indicating complex evolution history. In this paper, we use Lunar Reconnaissance Orbiter (LRO) Altimeter (LOLA) and Camera (LROC) data to characterize regional topography and geological features. We deduce the iron and titanium content from Clementine ultraviolet-visible (UVVIS) data and generate mineral absorption features from the Chandrayaan-1 Moon Mineralogy Mapper (M3) imaging spectrum data. Results show that this region has experienced four magmatic events. The composition of these basaltic materials filled in different time changes from low-titanium basalts in earlier time to medium-titanium basalts in later time. The inner Sinus Iridum has a composition of mature and pyroxene-rich materials, but olivine abundance of these pyroxene-rich materials increases from old to young. The surrounding highlands have a dominantly feldspathic composition. In the north wall, there exposed some possible mantle origin olivine-rich materials. The comparable flat topography condition and abundant geological features make Sinus Iridum an excellent site to carry out in-site analyses and rover exploration.

Geological Characteristics of Von Kármán Crater, Northwestern South Pole‐Aitken Basin: Chang'E‐4 Landing Site Region

Von Karman crater (diameterxa0=xa0~186xa0km), lying in the northwestern South Pole-Aitken (SPA) basin, was formed in the pre-Nectarian. The Von Karman crater floor was subsequently flooded with one or several generations of mare basalts during the Imbrian period. Numerous subsequent impact craters in the surrounding region delivered ejecta to the floor, together forming a rich sample of the SPA basin and farside geologic history. We studied in details the targeted landing region (45.0–46.0°S, 176.4–178.8°E) of the 2018 Chinese lunar mission ChangE-4, within the Von Karman crater. The topography of the landing region is generally flat at a baseline of ~60xa0m. Secondary craters and ejecta materials have covered most of the mare unit and can be traced back to at least four source craters (Finsen, Von Karman L, Von Karman L, and Antoniadi) based on preferential spatial orientations and crosscutting relationships. Extensive sinuous ridges and troughs are identified spatially related to Ba Jie crater (diameterxa0=xa0~4xa0km). Reflectance spectral variations due to difference in both composition and physical properties are observed among the ejecta from various-sized craters on the mare unit. The composition trends were used together with crater scaling relationships and estimates of regolith thickness to reconstruct the subsurface stratigraphy. The results reveal a complex geological history of the landing region and set the framework for the in situ measurements of the CE-4 mission, which will provide unique insights into the compositions of farside mare basalt, SPA compositional zone including SPA compositional anomaly and Mg-pyroxene annulus, regolith evolution, and the lunar space environment.