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Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India

2009; Geological Society of America; Volume: 122; Issue: 3-4 Linguagem: Inglês

10.1130/b26550.1

1943-2674

Saumitra Misra, Md. Arif, N. Basavaiah, Priyeshu Srivastava, A.K. Dube,

Geological and Geochemical Analysis

Research Article| March 01, 2010 Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India Saumitra Misra; Saumitra Misra † 1Indian Institute of Geomagnetism, Navi Mumbai 410 218, India †Present address: School of Geological Sciences, University of Kwazulu-Natal, Durban 4000, South Africa; E-mail: misrasaumitra@gmail.com; misras@ukzn.ac.za Search for other works by this author on: GSW Google Scholar Md. Arif; Md. Arif 1Indian Institute of Geomagnetism, Navi Mumbai 410 218, India Search for other works by this author on: GSW Google Scholar Nathani Basavaiah; Nathani Basavaiah 1Indian Institute of Geomagnetism, Navi Mumbai 410 218, India Search for other works by this author on: GSW Google Scholar P.K. Srivastava; P.K. Srivastava 2National Remote Sensing Center (ISRO), Hyderabad 500625, India Search for other works by this author on: GSW Google Scholar Anand Dube Anand Dube 3P147/3, Janak Road, Kolkata 700 029, India Search for other works by this author on: GSW Google Scholar Author and Article Information Saumitra Misra † 1Indian Institute of Geomagnetism, Navi Mumbai 410 218, India Md. Arif 1Indian Institute of Geomagnetism, Navi Mumbai 410 218, India Nathani Basavaiah 1Indian Institute of Geomagnetism, Navi Mumbai 410 218, India P.K. Srivastava 2National Remote Sensing Center (ISRO), Hyderabad 500625, India Anand Dube 3P147/3, Janak Road, Kolkata 700 029, India †Present address: School of Geological Sciences, University of Kwazulu-Natal, Durban 4000, South Africa; E-mail: misrasaumitra@gmail.com; misras@ukzn.ac.za Publisher: Geological Society of America Received: 18 Sep 2008 Revision Received: 13 May 2009 Accepted: 18 May 2009 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2010 Geological Society of America GSA Bulletin (2010) 122 (3-4): 563–574. https://doi.org/10.1130/B26550.1 Article history Received: 18 Sep 2008 Revision Received: 13 May 2009 Accepted: 18 May 2009 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Saumitra Misra, Md. Arif, Nathani Basavaiah, P.K. Srivastava, Anand Dube; Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India. GSA Bulletin 2010;; 122 (3-4): 563–574. doi: https://doi.org/10.1130/B26550.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The anisotropy of magnetic susceptibility (AMS) technique, combined with the analyses of satellite images and the geological structure, are examined on Lonar crater, a small, ∼1.8-km-diameter impact crater in India, to evaluate the direction and obliquity of asteroid impact. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image (15-m resolution) of the ca. 52 ka Lonar crater in the subhorizontal Deccan basalt (ca. 65 Ma) shows that this simple, bowl-shaped impact crater has a near-circular rim with a circularity of ∼0.95. Most of the highly reflecting, continuous-ejecta blanket around the crater rim can be enveloped with an ellipse whose major E-W axis is coincident with the diameter of the crater rim and minor N-S axis is relatively displaced toward the west by ∼200 m. The present ejecta distribution, which appears to be close to its pristine shape, extends to a distance of ∼700 m in all the directions from the crater rim except to the west where it extends to a distance of a little more than 1 km. The circular shape of the crater rim, the E-W bilateral symmetry of the enveloping ellipse on the ejecta, and the greater extension of the ejecta toward the west appear to be the result of an oblique impact from the east with an angle of incidence of 30°–45° when compared with experiments. The AMS data suggest that the target basalts occurring at ∼2 km west-southwest of the crater rim are highly shocked, as indicated by the random orientation of their K3 susceptibility axes in comparison to the unshocked basalts at ∼2 km east-southeast of the crater; the unshocked basalts show a bimodal distribution of susceptibility axes typical of lava flows. Moderate to strong westward shifts of the K3 axes are seen for the majority of the shocked basalts on the crater rim and west-southwest of the crater; the shocked basalts also indicate an oblique impact from the east when compared with modeling and experiments. A general lowering of degree of anisotropy of the Lonar shocked basalts (∼1.01) compared to the surrounding unshocked basalts (∼1.03) is found to be a characteristic feature of impact crater target rocks. Variation in attitudes of the basalt flows on the Lonar crater rim shows a bilaterally symmetrical distribution about an E-W axial plane, which includes quaquaversal dips of the flows all around the crater rim, except to the west where overturned dips of the basalt flows are seen. It appears that oblique impact and the symmetry in structural variations around the crater rim have a relationship for a small crater such as Lonar. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.