Magnetic Anomaly and Model of the Lonar Meteorite Impact Crater in Maharashtra, India

Abstract

The ground magnetic field of the Lonar impact crater (Maharashtra State, India) and its surrounding area was measured and studied utilizing 2.5-dimensional potential field modelling. Field data showed the crater depression is associated with a strong circular negative anomaly with an amplitude of more than 1000 nT. The negative anomaly, however, decreases smoothly while moving from south to north. Most of the crater rim exhibits anomalous positive values. Negative anomalies at the rim are seen in the south - southwestern sections and coinciding in the northeastern section with the Dhar valley. Our study shows that most of the anomaly is caused by the topographic effect and a strong SE directed natural remanent magnetization of Deccan Trap basalts, which are the target of the Lonar-creating projectile. The magnetic anomaly of the relatively weakly magnetized impact-produced allochthonous breccia and post-impact sediments is small, being less than 150 nT.

3D geometry of the Lonar impact crater, India, imaged from cultural seismic noise

“…The crater's depth was modelled to be about 500-600 m below the surface. In contrast, Kiik et al (2020) observed a negative magnetic anomaly over the crater and concluded that the post-impact brecciation and random distribution of clasts weaken the remanent magnetization compared to the surrounding Deccan basalts. Such a discrepancy in the magnetic model may arise from the complex nature of the breccia zone, which is largely unknown.…”

“…Using the first three drill holes, Fredriksson et al (1973) produced a depth cross-section showing a sedimentary layer with a maximum thickness of 100 m overlying a brecciated zone whose thickness exceeds 225 m. Later, Fudali et al (1980) concluded that four of the five drill holes did not actually reach the true bottom of the crater. Additionally, no consistent core-to-core correlation from all five drill holes was obtained, indicating that the exact extent of the brecciated zone is unknown (Fudali et al 1980;Kiik et al 2020).…”

“…Numerous studies, including drilling, gravity, magnetic, and seismic investigations, have attempted to provide the geometry of the Lonar crater. The early model of the crater, obtained from drill holes up to 310-400 m below the floor level (Fredriksson et al 1973;Fudali et al 1980), shows a sedimentary layer with a maximum thickness of 100 m underlain by brecciated rocks and the crater's depth exceeding 400 m. Rajasekhar & Mishra (2005) and Kiik et al (2020) observed circular/semi-circular gravity and magnetic anomalies and estimated the crater's true depth to be about 500-600 m. A recent study by Sivaram et al (2018), using ambient noise and theoretically computed higher mode surface waves (0.2 to 20 Hz), provided a shear wave velocity model of the crater up to 750 m depth. Due to a low lateral resolution (> 2 km) and a limited vertical extent of the velocity model, they failed to provide the detailed geometry of the crater.…”

Numerical simulation of meteorite impact on basaltic lavas at Lonar Crater, India

“…It provides a unique opportunity to study crater structures analogues to extraterrestrial craters on the bodies like Moon and the Mars [2][3][4] Despite a few attempts, the nature of the impactor is still not clear. The field survey shows the presence of maskelynite fragments and deformational features which confirm hypervelocity impact as the cause of the formation of Lonar crater [2,4,5]. Lakshmi and Kumar [4] have investigated impact and deduced that the impactor was of radius (R) 35m and density (ρ) 2900 kg/m 3 , with 20 km/s impact velocity (v).…”

“…The exercise is carried out with two target materials: basalt and bilayer of basalt and granite. The thickness of the basaltic lavas is taken as per known estimates of 500 m [5].…”