Secular Change of Preservation of Lunar Sinuous Rilles: Constraints from Lava Flow Numerical Modeling

Lunar mare basalts, produced by the partial melting of the lunar mantle, provide key insights into volcanic activity and thermal evolution of the Moon. China's lunar exploration mission, Chang'e-5 (CE-5), sampled mare basalts in the Northern Oceanus Procellarum, close to a sinuous rille, Rima Sharp. Sinuous rilles are meandering channel-like depressions formed by basaltic lava flows; however, their origin and evolution remain debatable, even though nearly 200 examples have been identified. Here, we use Cellular Automata to explore how lunar basaltic lava flows dictate the preservation potential of pre-existing sinuous rilles. Specifically, we model lavas as Bingham fluids, constrained by physical properties of the returned CE-5 sample, that flow on a sloped plane and interact with rilles of different sinuosities (i.e., degrees of meandering). Our results show that most rilles are preserved when eruptions last 10a s (∼1 day) at effusion rates of 1.2 × 10⁴–8 × 10⁴ m³/s, that is, mare regions hosting sinuous rilles likely did not experience intense volcanic activities since rille formation. We also recognize an increase in the area density of sinuous rilles—total rille lengths per unit area of mare basalts—through time that is consistent with our modeling. Overall, our findings suggest that early stage volcanism on the Moon (3.8–3.4 Ga) was more intense and had lower preservation potential of rilles than a milder late stage (2.0–1.2 Ga). These findings constrain the preservation conditions of rilles, offering new insights into their evolution and contributing to a broader understanding of lunar volcanic and thermal history.