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    Geochemical identification of impactor for Lonar crater, India

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    Author
    Misra, S.
    Newsom, H. E.
    Shyam Prasad, M. Shyam
    Geissman, J. W.
    Dube, A.
    Sengupta, D.
    Issue Date
    2009-01-01
    Keywords
    meteorite impact craters
    basaltic target rocks
    impact spherules
    chondritic impactor
    
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    Citation
    Misra, S., Newsom, H. E., Shyam Prasad, M., Geissman, J. W., Dube, A., & Sengupta, D. (2009). Geochemical identification of impactor for Lonar crater, India. Meteoritics & Planetary Science, 44(7), 1001-1018.
    Publisher
    The Meteoritical Society
    Journal
    Meteoritics & Planetary Science
    URI
    http://hdl.handle.net/10150/656591
    DOI
    10.1111/j.1945-5100.2009.tb00784.x
    Additional Links
    https://meteoritical.org/
    Abstract
    The only well-known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the Lonar crater, India. For the first time, evidence of the impactor that formed the crater has been identified within the impact spherules, which are ~0.3 to 1 mm in size and of different aerodynamic shapes including spheres, teardrops, cylinders, dumbbells and spindles. They were found in ejecta on the rim of the crater. The spherules have high magnetic susceptibility (from 0.31 to 0.02 SI-mass) and natural remanent magnetization (NRM) intensity. Both NRM and saturation isothermal remanent magnetization (SIRM) intensity are ~2 Am2/kg. Demagnetization response by the NRM suggests a complicated history of remanence acquisition. The spherules show schlieren structure described by chains of tiny dendritic and octahedral-shaped magnetite crystals indicating their quenching from liquid droplets. Microprobe analyses show that, relative to the target basalt compositions, the spherules have relatively high average Fe2O3 (by ~1.5 wt%), MgO (~1 wt%), Mn (~200 ppm), Cr (~200 ppm), Co (~50 ppm), Ni (~1000 ppm) and Zn (~70 ppm), and low Na2O (~1 wt%) and P2O5 (~0.2 wt%). Very high Ni contents, up to 14 times the average content of Lonar basalt, require the presence of a meteoritic component in these spherules. We interpret the high Ni, Cr, and Co abundances in these spherules to indicate that the impactor of the Lonar crater was a chondrite, which is present in abundances of 12 to 20 percent by weight in these impact spherules. Relatively high Zn yet low Na2O and P2O5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume.
    Type
    Article
    text
    Language
    en
    ISSN
    1945-5100
    ae974a485f413a2113503eed53cd6c53
    10.1111/j.1945-5100.2009.tb00784.x
    Scopus Count
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    Meteoritics & Planetary Science, Volume 44, Number 7 (2009)

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