Distribution of Impact-induced Stress around Lonar

Introduction: The 52±6 ka old Lonar crater, India [1, 2], is the only known terrestrial impact crater in basaltic target-rocks (Deccan Traps, ~65 Ma). The impactor asteroid of this ~1.8 km diameter crater was perhaps a chondrite [3] that hit the pre-impact surface from east at an angle of 30-45 o with horizon [4]. Presently, we report the possible distribution of impact-induced stress around Lonar crater using Anisotropy of Magnetic Susceptibility (AMS) technique and also variations in Natural Remanent Magnetization (NRM) with reference to the direction of impact. Experimental Procedures: Oriented drill cores of shocked basalts and apparently unshocked basalts were collected from all around the crater rim and at ~2 km east from the crater rim respectively. The AMS measurements were carried out by an AGICO KLY-4S Kappabridge instrument with an alternating field intensity of 300 Am-1 and operating frequency of 875 Hz. The NRM was measured by a Molspin Spinner Magnetometer. Results: The K 3 axes of AMS of shocked basalts collected from the eastern, southeastern, and northern sectors along the crater rim show a major westward shift. A southwest-ward shift of K 3 axes is noticed for shocked basalts from the southern and southwestern sectors of the crater rim, and for samples from near the Kalapani dam and Khini village situated at ~2 km WSW of crater. The samples from west-northwest and northwest sectors of crater rim and from the Saraswati village, ~2 km NW of crater, show a major northwest-ward shift of K 3 axes. The unshocked basalts ≥2 km away from crater rim have an average NRM of ~5 Am-1. The shocked basalts from Kalapani dam, however, show a lower NRM of an average of ~2.6 Am