Formation and geomorphologic history of the Lonar impact crater deduced from in situ cosmogenic 10 Be and 26 Al

Abstract

The Lonar impact crater is one of a few craters on Earth formed directly in basalt, providing a unique opportunity to study an analog for crater degradation processes on Mars. Here we present surface 10 Be and 26 Al exposure dates in order to determine the age and geomorphic evolution of Lonar crater. Together with a 14 C age of preimpact soil, we obtain a crater age of 37.5 ± 5.0 ka, which contrasts with a recently reported and apparently older 40 Ar/ 39 Ar age (570 ± 47 ka). This suggests that the 40 Ar/ 39 Ar age may have been affected by inherited radiogenic 40 Ar ( 40 Ar ∗ inherited) in the impact glass. The spatial distribution of surface exposure ages of Lonar crater differs from that for Barringer crater, indicating Lonar crater rim is actively eroding. Our new chronology provides a unique opportunity to compare the geomorphological history of the two craters, which have similar ages and diameters, but are located in different climate and geologic settings.