FIELD AND HANDLENS GEOLOGY AT LONAR CRATER, INDIA: DISTINGUISHING SMALL SCALE FEATURES OF IMPACT FROM THOSE OF BASALTIC VOLCANISM AND IMPLICATIONS FOR MARS LANDERS/ROVERS

An important goal of the Mars Program is characterizing the geologic history of Mars. Two important processes occurring throughout Mars history are basaltic volcanism and impact cratering, but generally there has been some debate over which process most recently affected the landscapes and rock textures of the first several Mars landers. The advent of rovers and a Microscopic Imager (MI) helped to provide constraints on small scale textures of martian rocks, but, with lack of well-preserved terrestrial impact craters, little is known about the textures and morphologies produced where basalt is subject to a wide range of shock pressures that results in shatterconing up to impact melts. These data might enable quick identification of the geologic history of talus, breccia clasts, and outcrop rocks encountered by current and future Mars rovers/landers. Whereas basaltic volcanism can potentially create breccias and glasses, these are generally of a different morphology than those created from impact. Lonar Crater, India provides an opportunity to examine basalt that has been shock metamorphosed. Fortuitously, the target Deccan basalt has been labeled as an excellent analog for basalt on Mars, as the laboratory thermal infrared spectrum of Deccan basalt being a close match to orbital spectral end-member Surface Type 1. Further, the TIR spectrum of intermediately (20-40 GPa) shocked Lonar basalt is identical to that of the Los Angeles shergottite. 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 and diagrams will be shown detailing these lithic and suevite (glassy) ejecta layers along with textures of rock surfaces produced by the impact process rather than basaltic volcanism. Images of Lonar impactites at the handlens scale analogous to those from the MER Microscopic Imager will be shown along with other examples of suevite and impact breccia textures from other terrestrial impact sites such as Meteor Crater, Arizona, Campo del Cielo, Argentina, and recent field trips of the Impact Field Studies Group. Lastly, local PanCam and MI images from MER sites will be shown of rocks that may be impact-generated.