Origin of lunar sinuous rilles:modeling effects of gravity, surface slope, and lava composition on erosion rates during the formation of Rima Prinz

摘要

Lunar sinuous rilles have long been interpreted as features that formed as the result of surficial lava flow, though the precise mechanism responsible for channel formation (constructed versus eroded origins) is still debated. In assessing the origin of Rima Prinz, a channel interpreted to have formed by erosion, two erosion regimes, mechanical and thermal, are considered. Measurements of channel dimensions are used as inputs to analytical models to constrain the origin of Rima Prinz, including lava compositions, mechanical and thermal erosion rates, eruption durations, and lava volumes required to form the feature. Key results indicate that Rima Prinz and other large sinuous rilles could have formed as the result of thermal erosion under the weak gravity and low slope conditions characteristic of these lunar features. Further analysis indicates that lava composition has significant effects on channel formation. Model results of four considered lava compositions show that komatiite-like lava will erode a similarly composed substrate most efficiently whereas a high-Ti basalt will erode a similarly composed substrate least efficiently; ocean island basalt and low-Ti basalt erode similarly composed substrates at intermediate rates. Results indicate that Rima Prinz may have formed over 0.4–2.2 Earth years, depositing 50–250 km3 of lava over a plausible deposit area of 2450 km2. Resulting deposit thicknesses suggest that the lava that incised Rima Prinz was most likely similar in composition to a terrestrial komatiite, ocean island basalt, or lunar low-Ti basalt. Further constraints on sinuous rille formation will serve as a window into the nature of volcanic activity of the Moon's past.