Abstract In spite of great scientific and engineering interests in lunar exploration, natural dust activity near the Moon surface remains unclear. According to distinct reflectance features of lunar rocks and regolith observed by Chang'E‐3 mission, long‐term dust activity near a young surface is quantified with a new method. We found that a dust deposition upper line on rocks is about 28 cm above the ground. Below this line, the quantity of dust deposits becomes smaller as the altitude ascends, whereas above the line, no visible or only negligible amount of dust is distributed on the rocks. This dust distribution pattern could be explained by dust electrostatic levitation process. The results indicate distinctively weak long‐term dust activity near the young surface and suggest possible selection of geologically young regions as landing sites or lunar bases to minimize the effect of dust grains.
Abstract Diverse polygonal patterned grounds are found to occur in the Eridania basin system (a set of connecting irregular‐shaped depressions interpreted as a paleolake basin system) located in the martian highland region between Terra Cimmeria and Sirenum. We here use multiple sets of imagery to document diverse polygonal patterned grounds in the fluvio‐lacustrine deposits of the northern Eridania basin, and interpret their formation mechanisms. The combination of detailed geomorphological mapping, morphometrical analyses, and investigation of the spatial distribution of polygonal patterned grounds with other geologic features leads us to conclude that (1) desiccation process within the clay‐rich materials would primarily contribute to the formation of cracked polygons, while the ridged polygons are best explained by mineral‐filled fractures that have been cemented and variably indurated by fluids; (2) the correlation between polygon size and topography is observed in the northern smooth light‐toned basement units, which can be best explained by the concentration of salt minerals (such as sulfate) in topographic lows so that the growth of fracturing is inhibited; (3) the large polygonal ridges formed in the knobby light‐toned terrains show a spatial distribution and a trend controlled by basin‐scale compressional tectonics and influenced by preexisting topography, for example, impact structures; (4) the linear fracture‐to‐ridge gradation indicates that the polygonal ridges in chlorides might be guided by the subjacent cracks occurring within clay‐rich materials; (5) both features (cracks and ridges) in some places may have formed simultaneously and are spatially distinct due to differences in erosional states; and (6) geologic features show a wealth of information of multiple aqueous events with the evaporation of the last liquid water ponding to form the southern playa where chloride salt precipitates. Crater retention age determination for the chloride‐bearing basement unit places a lower limit for the cessation of the local aqueous events to ∼3.29 Ga, indicating that the open‐system‐style alteration by surface waters on Mars might have continued in the period of the Late Hesperian to Early Amazonian.
High-Mg diorites with high Sr/Y ratios are commonly associated with metal mineralization. But their petrogenesis still remains controversial. Here we present a case study of the Early Cretaceous high-Mg dioritic intrusions (Fushan intrusive complex) in the Handan-Xingtai district, central North China Craton (NCC). Samples from the Fushan Complex (123±1 Ma) have SiO2 of 53.3–62.6 wt%, relatively variable K2O of 0.5–3.6 wt%, and high Mg# values (44–63). They show enrichment in light rare earth elements and depletion in heavy rare earth elements and high field strength elements, with high Sr/Y ratios and insignificant Eu anomalies, similar to those of adakitic rocks. For the Sr-Nd isotopes, they have whole-rock initial 87Sr/86Sr ratios and εNd(t=123 Ma) values ranging from 0.706564 to 0.707546 and from −16.1 to −12.8, respectively, which are distinct from those in the lower continental crust but similar to those in the contemporaneous mafic rocks in the study area. Because of these characteristics, together with their zircon δ18O values of 6.6‰±0.4‰, we suggest that the Fushan high-Mg dioritic complex was most likely formed by factional crystallization of mantle-derived basaltic magma. The high Sr/Y ratios could be achieved by the fractionation of amphibole crystals plus significant volumes of feldspars from a mafic magma. We suggest that late Mesozoic strong lithospheric extension and thinning, caused by the subduction of the paleo-Pacific slab in the east of the NCC, might have triggered the melting of the metasomatic lithospheric mantle to generate these intrusive complexes in the Handan-Xingtai district.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3c/svg%3e)
