A WEALTH OF ANALOG PROCESSES, LITHOLOGIES, AND FIELD LOCALITIES AT LONAR CRATER, INDIA REGARDING BASALTIC VOLCANISM, ALTERATION, AND SHOCK

“There is no perfect analog for Mars on Earth” [first line of Hipkin et al., 2013]. However, fieldwork and corresponding sample analyses from laboratory instrumentation (to proxy field instruments) suggest that mission training for both humans and rovers would be beneficial to the goals of future Artemis missions to the Moon and perhaps future Mars rovers, respectively. Three aspects are briefly described below.

Analog Processes: The geologic history of Lonar crater with products numbered include: 1.) flood basaltic volcanism with interlayer development of 2.) baked zones/“boles” and 3.) soil formation. Of six flows, the lower three are aqueously altered [Maloof et al., 2010] to produce 4.) alteration products described below. The impact event ~570 ka [Jourdan et al., 2011] produced 5.) impactites of all of these protoliths (#1 through 4) [Kieffer et al., 1976].

Analog Lithologies: 65 Ma Deccan basalt contains augite and labradorite. Baked zones are higher in hematite and other iron oxides. Soil consists of calcite and organic matter. Secondary alteration includes hematite, chlorite, serpentine, zeolite, and palagonite. These lithologies (#1 through 4 above) are shocked to produce maskelynite, flowing plagioclase glass, vesiculated plagioclase glass, and complete impact melts. Pre-impact alteration materials have been shock metamorphosed to become shocked baked zones and shocked soil [Wright and Michalski, JGR-Planets, 2024].

Fieldwork: The ejecta consists of two layers: 8 m of lithic breccia with unshocked and fractured basalts under a 1 m suevite breccia consisting of all ranges of shock pressure described above for labradorite. The alteration mineralogy of every ejecta lobe is being mapped at a detailed scale to rival Shoemaker’s at Meteor Crater that spurred the work. Two alteration mineralogies commonly have an association or “grouping” in ejecta lobes with two other separate lithologies. These emplacements in the ejecta suggest a close proximity in the pre-impact stratigraphy. One of these associations was found ~25 km west of Lonar as a baked zone overlying a 2nd lithology. The final Ejecta Outcrop Map will show these “Lithologies” (#1 through 5 above) of all lobes as the beginning of a larger field guide in the hopes that mission training for rovers or humans will include Lonar crater ejecta.