Fieldwork at Lonar Crater, India: Analog for Lunar Impact Sites Emplaced into Basaltic Target Rocks

After the initial emplacement/cooling of basalt or anorthosite, impact cratering is the dominant geologic process modifying the surface and soil of the Moon. However, there are few opportunities for future lunar field geologists to study well-preserved terrestrial impact sites in preparation for lunar fieldwork. It has been and will be beneficial for analog fieldwork to take place at Meteor Crater, Arizona, USA, though the sedimentary target rocks are not analogous to the Moon. In this presentation, previous and recent field data of Meteor Crater will be discussed along with aspects of the structure and composition of the only known terrestrial impact crater emplaced into basaltic target rocks. Lonar Crater, India, provides an opportunity to examine basalt subjected to a wide range of shock pressures that results in the creation of maskelynite up to the generation of basaltic impact melts. An impact ~50 ka into a sequence of six ~65 Ma Deccan flood basalt flows created a crater 1.8 km in diameter and two layers of ejecta. Field images, diagrams, remote images, and thermal infrared data will be shown detailing the locations and characteristics of these lithic and suevite (glassy) ejecta layers. These data might enable quick identification of the geologic history of talus, breccia clasts, and outcrop rocks encountered by lunar rovers and field geologists to assist in sample collection. Whereas basaltic volcanism can potentially create breccias and glasses, these are generally of a different morphology than those created from impact. The same ejecta facies for Meteor Crater will be shown as well. As can be expected, whereas the effects of wind and water are not seen in remote studies of the modification of lunar craters, these volatiles have affected the mineralogy, extent, and other characteristics of the Lonar Crater ejecta blanket and inner-crater melt breccias.