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A rock magnetic profile through the ejecta flap of the Lockne impact crater (central Sweden) and implications for the impact excavation process

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Melero Asensio, Irene and Martín Hernández, Fátima and Ormoe, Jens (2015) A rock magnetic profile through the ejecta flap of the Lockne impact crater (central Sweden) and implications for the impact excavation process. Journal of applied geophysics, 122 . pp. 91-105. ISSN 0926-9851

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Official URL: http://dx.doi.org/10.1016/j.jappgeo.2014.11.009


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Abstract

The well-documented, well-preserved, and well-exposed Lockne crater is a reference crater for marine-target impacts on Earth. The large amount of data allows detailed analysis of the cratering and modification processes. A unique feature of Lockne as compared with other similar craters is its pristine ejecta layer. Here, we provide the first complete lithological description coupled with an analysis of the rock magnetic properties of the Lockne-9 core drilled through the ejecta flap. Low-field bulk magnetic susceptibility, magnetic hysteresis, isothermal remanent magnetization curves (IRM), and the corresponding model of the coercivity spectra, backfield IRM, and thermomagnetic curves are used to fully characterize the magnetic mineralogy (i.e., pseudo-single domain (PSD) magnetite and pyrite). Variation of the magnetic properties with depth reveals a characteristic maximum in the magnetic susceptibility and magnetization within the crystalline ejecta. The magnetic properties of rocks affected by the impact show a slight weakening in the coercivity of magnetic minerals in comparison with rocks not affected by the impact Altogether, this suggests to us that the high magnetization zone already existed before the impact event took place. Therefore, it can be inferred that during the cratering process, the Lockne ejecta was repositioned en masse from the central part of the crater in the form of an ejecta flap. This stands in contrast to the standard ballistic emplacement model wherein individual particles move in an ejecta curtain.


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© 2014 Elsevier. The work by I. Melero-Asensio and J. Ormö is partially supported by grants AYA2008-03467/ESP and AYA2011-24780-ESP. F. Martín-Hernández was partially funded by a Ramón y Cajal contract, all from the Spanish Ministry of Economy Competitiveness. The authors are grateful for the laboratory assistance by S. Guerrero-Suárez and V. Villasante from the UCM and M. P. Martín-Redondo and M. T. Rodríguez-Sampedro from the CAB. We acknowledge Professor David T. King Jr. at the Auburn University (AL, USA) for his help with the linguistics. We appreciate the helpful comments by the reviewers that greatly improved the paper.

Uncontrolled Keywords:Isothermal remanent magnetization; Acquisition curves; Ordovician lockne; Marine; Jamtland; Coercivity; Components; Tvaren; Demagnetization; Susceptibility
Subjects:Sciences > Physics > Geophysics
Sciences > Physics > Meteorology
ID Code:30465
Deposited On:29 May 2015 18:52
Last Modified:29 May 2015 18:52

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