A WEALTH OF ANALOG LITHOLOGIES AND FIELD LOCALITIES AT LONAR CRATER, INDIA REGARDING BASALTIC VOLCANISM, ALTERATION, AND SHOCK
Analog Processes: The geologic history of Lonar Crater emulates localities on Mars with 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. Several basalts with secondary alteration are listed here and these mirror alteration on Mars: hematite, chlorite, serpentine, zeolite, and palagonite, with varying combinations of these with primary igneous minerals. All of these lithologies (#1 through 4 above) are shocked to produce maskelynite, flowing plagioclase glass, vesiculated plagioclase glass, and complete impact melts.
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.