Variation of primary magnetization of basaltic target rocks due to asteroid impact: example from lonar crater, India

Abstract

Lonar lake, India [1, 2] is one of the few known terrestrial asteroid impact craters that is fully excavated in Deccan Trap basalts (~65 Ma) [3], and thus comparable to those craters formed on rocky planetary bodies in our Solar System having basaltic crusts [4]. This simple, bowl-shaped, near-circular impact crater has a diameter of ~1.8 km with an average rim height of ~30 m above the adjacent plains, whereas the crater floor lies ~90 m below the preimpact surface [5]. The age of the crater is controversial and could be ~52±6 [6] or 656±81 ka [7]. This crater was formed by an oblique impact of a chondrite that hit the pre-impact target at an angle bewteen 30-45o from the east [8, 9]. Our preliminary observations showed that the unshocked and shocked basalts from Lonar significantly differ in their bulk-coercivity, squareness of hysteresis, coercivity ratio, and low and high temperature susceptibility measurements [10]. It is also understood that anisotropy of magnetic susceptibility (AMS) of unshocked and shocked target basalts show systematic variations with reference to the direction of impact [9, 11]. In the present work, we report variations in primary magnetization component between the unshocked and shocked target rocks of Lonar crater and their relation to the direction of impact.