A compendium of the best-preserved terrestrial hypervelocity impact crater in a basaltic terrain: The Lonar, India

Document Type

Article

Publication Date

8-2023

Department

Department of Geological and Mining Engineering and Sciences

Abstract

As impact cratering is regarded as the most fundamental process in the modification of planetary surfaces, it is crucial to investigate and identify terrestrial impact craters with credible evidences to learn more about the planet's evolutionary path. Consequently, terrestrial impact craters are considered as proxies for planetary explorations. However, because of the diversity of the lithologies the terrestrial craters are carved in, those in basaltic rocks, which make up the majority of planets, are thought to be the best candidates. Lonar Impact Crater in India is a well-preserved, simple bowl-shaped impact crater that is etched in tholeiitic basalt of the ~65 Ma Deccan Volcanic Province (DVP). The crater has a diameter of 1.88 km and a depth of ~150 m. Being a basaltic target and situated in warm temperate climatic zone, apart from the modern-day anthropogenic influence, the crater is subjected to denudation. One such study has quantified a cumulative rim erosion of 30 m and an erosion rate at 96–203 mm per kyr, indicating fast denudation of the crater. Several methods were employed to date the impact event and based on the recent in-situ cosmogenic radionuclide dating, the age is determined as 37.5 ± 5.0 ka. The tholeiitic flood basalt target rock at Lonar exhibits high total iron (26.25 wt%) and CaO content (9.97 wt%) with lower contents of Al2O3 (13.21 wt%) and MgO (5.96 wt%). Based on the Ni (~60 to 2500 ppm), Cr (27 to 618 ppm), and Co (38 to 196 ppm) geochemistry of sub-mm sized Lonar spherules, the most likely projectiles associated with the cratering event are the chondritic impactors. The Mesoarchean age (~3.0 to 3.1 Ga), yielded by a few zircon grains separated from an impact melt-bearing breccia together with the exotic quartz grains with impact features like planar deformation feature, which is unfamiliar in a basalt-dominated impactite, proved the incorporation of the deep-seated Archean Peninsular gneiss in the impact event. This demonstrates a depth penetration of 522–570 m for the impact. However, compared to the extent of ejecta seen in comparable younger craters on the Moon and Mars, where ejecta can travel up to distances of ~10R and ~ 15R, respectively, the expanse of spallation from the terrestrial Lonar crater is only visible in a smaller area (~3R). In the entirety, Lonar crater has been explored by many researchers, which have uncovered many aspects of the impact including ejecta particles, structural, magnetic, hydrological, and geophysical characterization. In order to better understand the cratering mechanism and characteristics of Lonar impact crater, this review paper aims to garner information from all the relevant literature and this compendium will act as a comprehensive synthesis that will reshape our understanding of not only Lonar impact crater but also the broader realms of impact cratering science.

Publication Title

Earth-Science Reviews

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