THE EMPLACEMENT OF VALLIS SCHROTERI AND MARE IMBRIUM LAVA FLOWS, THE MOON

Two of the largest volcanic features on the lunar surface are Vallis Schroteri on the Aristarchus Plateau and the well-preserved flow lobes in Mare Imbrium. Data from Lunar Reconnaissance Orbiter (LRO) has revealed new details about the morphology of these two features. The cobra head is a low shield that surrounds the source vent of Vallis Schroteri. Topography data from LRO shows that there are two peaks of similar heights on the cobra head, suggesting two eruptive vents. The floor of the primary rille is at a similar elevation to the surrounding mare units, but it is unclear if this depth is due to thermal erosion, mechanical erosion, and/or construction by lava. Layered outcrops are exposed along the upper part of the rille wall suggesting a sequence of basaltic rocks, but debris obscures the stratigraphy along the base. The flow field in Mare Imbrium erupted in three phases over a period of 0.5 billion years (3.0-2.5 Ga) and originated from a series of buried vents near Euler crater. Morphologic mapping reveals a different flow path for Phase I compared to the original mapping completed by Schaber (1973). Flow features and margins have been identified in the Phase I flow in both LROC WAC and NAC images. LOLA profiles over the more prominent flow lobes in Phase I reveal they are less than 10 m thick. Phase II and III morphology maps are similar to previous flow maps. Phase III lobes near Euler are 10-12 km wide and 20-30 m thick based on measurements of the LOLA 1024ppd elevation Digital Terrain Model (DTM) in JMoon. One of the longer Phase III lobes varies between 15 to 50 km wide and 25 to 60 m thick, with the thickest section at the distal end of the lobe. The Phase II lobe is 15 to 25 m thick and up to 35 km wide. The morphology of these two features must be constrained prior to numerical modeling. Here, we will present recent morphologic mapping and qualitative emplacement scenarios for these features.