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GSA Data Repository Item 2009221
Appendix A: Technical details of ASTER image of Lonar crater
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Multi-spectral Advanced Spaceborne Thermal Emission and Reflection Radiometer
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(ASTER) imagery, acquired on April 8, 2003 and January 21, 2004 at 11.09 a.m. (IST) (LPDAAC,
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2007), was used to investigate the shape of the Lonar crater and distribution of ejecta around it (Fig.
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1a). The ASTER is the Earth’s first spaceborne multispectral Thermal Infrared Radiometer (TIR)
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instrument that has recently been used to obtain and interpret high spatial resolution images of
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terrestrial geological features including asteroid impact craters (e.g., Rowan et al., 2005; Wright and
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Ramsay, 2006). The Lonar crater was also examined with a panchromatic Landsat 7 image of 15 m
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spatial resolution (Misra et al., 2006). The advantage of the ASTER image is that it produces a
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better image in the same spatial resolution (15m) in the Visible and Near-Infrared Radiometer
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(VNIR) bands and better spectral resolution in the Short Wave Infrared Radiometer (SWIR) (6
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bands) and Thermal Infrared Radiometer (TIR) bands (5 bands) as well. A higher number of SWIR
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and TIR bands also provide important information on mineral composition on land surfaces
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(Vaughan et al., 2005). Two scenes captured on different dates (see above) were obtained to
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minimize the effect of the sun angle and enhanced the shape of the Lonar crater.
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Appendix B: Sampling and Experimental techniques of AMS study of Lonar crater
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Oriented drill core samples of diameter 2.5 cm along the Lonar crater rim and adjacent area
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were collected (Fig. 1d) during our June’2008 field trip using a gasoline-powered rock drill. We
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collected basalt samples from locations (one each) from the eastern, southeastern, southern,
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southwestern, western and northwestern sectors of the crater rim. The target basalt at the northern
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crater rim was extremely brittle in nature and it was very difficult to collect drill cores of full length
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(~7-9 cm) from this sector. Therefore, drill cores of relatively smaller length (3-5 cm) from two
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locations at this sector were collected. No sampling was possible from the northeastern crater rim
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sector because of the absence of a rim in this part of the crater due to faulting (Fig. 1a). Cores were
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cut into four cylindrical specimens in maximum of height 2.2 cm each in the laboratory. The AMS
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(low-field) was measured using an AGICO (Czech Republic) KLY-4S Kappabridge with an
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alternating field intensity of 300 A/m and an operating frequency of 875 Hz (AGICO, 2004) at the
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Environmental Magnetism Laboratory, Indian Institute of Geomagnetism, Navi Mumbai, India. The
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specimen susceptibility was measured manually in fifteen different orientations following a
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rotatable design, from which six independent components of the susceptibility tensor and statistical
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errors were calculated using the software SUFAM (Jelinek, 1978). Additional drill core samples
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were also collected during our February’2009 field trip and two to four specimens of height 2.0 cm
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each were cut from the each drill core for measurement of AMS in spinning specimen method using
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the same instrument. In this technique 64 x 3 measurements were made along three orthogonal
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directions with reference to the drill core axis of each specimen and the software SUFAR was used
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for computation of the AMS parameters. Besides the studies on the orientations of AMS principal
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susceptibility axes, the following two mathematical parameters (after Jelinek, 1978) were also
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considered for interpreting the Lonar samples:
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Degree of anisotropy (P/) = exp [2*Σ (ln Ki/K)2]1/2 where i= 1 to 3, and the
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Shape parameter (T) = [(2*ln K2- ln K1- ln K3)/(ln K1- ln K3)],
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where ‘exp’ and ‘ln’ means exponential and natural logarithm respectively; K1, K2 and K3 are the
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maximum, intermediate and minimum susceptibility axes, and
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K (mean susceptibility) = (K1+ K2+ K3)/3.
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Additionally, a parameter called ‘degree of anisotropy (A)’ that quantified the departure
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from the isotropic case (when all three principal susceptibilities are equal) (after Cañón-Tapia et al.,
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1997) was also used for our samples for further comparison, where
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A= 100 *{1-[(K3+K2)/2K1]}
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and ‘A’ ranges between 0% (isotropic) to 100% (K1>> K2 and K3).
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Figure captions in GSA data repository
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Figure GSA DR-1
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(a) Ejecta profile at Kalapani dam area at the SW of the Lonar crater. Soil horizon formed by
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erosion of ejecta at higher altitude [S] forms a cap on the distant ejecta [E] resting over paleosol
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[P]; chisel marking the boundary between top soil layer and ejecta cover; hammer head indicates
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the boundary between ejecta cover and underlying paleosol. The boundary between ejecta and
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underlying paleosol is less distinct due to CaCO3 veins leached from the ejecta cap during
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weathering. The height of exposure is ~1.6 m.
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(b) Sub-horizontal basalt flows at ~2 km ESE of the Lonar crater at Durga Tegri area showing semi-
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continuous flow-parallel fractures (shown by horizontal arrows) and less-common sub-vertical
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fractures (shown by vertical arrows pointing downward) in cross-section; total thickness of
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exposure is ~3.5 m.
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(c) Plan view of an exposure of shocked basalt on crater rim at SSE sector showing fracture
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cleavage; the attitude of cleavage is shown by a symbol, which dips towards the crater
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depression (note arrow).
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(d) Plan view of basalt on crater rim at the SSW sector showing a set of widely spaced fractures,
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arrow indicates direction of dip of fractures towards the crater depression; scale- hammer with
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length ~39 cm.
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(e) Cross-sectional view of a remnant basalt flow in the WSW sector showing overturned dip;
hammer (~39 cm) showing attitude of flows; black arrow points to crater depression.
(f) Basalt flow with flow-parallel cleavage at the WNW sector showing overturned dip (crosssectional view); hammer is placed parallel to flow; arrow points to the crater depression.
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(g) Cross-sectional view of the ejecta at the north of the Lonar crater. Note an angular piece of
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shocked basalt within ejecta showing development of strong fracture cleavage due to impact
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(double-headed arrow shows trend of fracture). Hammer head indicates bottom of the section.
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(h) A piece of maskelynite from within ejecta showing development of a strong fracture cleavage
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(P) and a secondary weak cleavage (S) in cross section; coin (1.8 cm) scale.
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Figure GSA DR-2
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Orientations of basalt flows (solid Gray Square) and fracture cleavage (open square) occurring
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on rim of the Lonar crater in the lower hemisphere of the π-pole diagram. For details see text.
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Figure GSA DR-3
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P/-T plots for unshocked and shocked basalts from around the Lonar crater (for sample locations
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see figure 1d). Note the higher P/ value and oblate shape of susceptibility ellipsoid are the
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characteristics of unshocked target basalts (a), whereas the shocked basalts have restricted and
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lower P/ values with the variation of shape of susceptibility ellipsoid from oblate to prolate (b-i).
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Relationship between P/ and A parameters (Cañón-Tapia et al., 1997) is shown in (j);
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abbreviations: DT: target basalt samples from Durga Tegri, CR-E: samples from the eastern
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crater rim sector, CR-rest: samples from rest of the crater rim, Khini: samples from Khini
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village.
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Figure GSA DR-4
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The lower hemisphere stereographic projections of AMS susceptibility axes (symbols as in
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figure 3) and P/-T plots of shocked basalts from the eastern cross-section of the Lonar crater
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below the rest house. Note relatively clustering of AMS susceptibility axes for basalts from
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higher altitude (~560 m) and distribution of K2 and K3 susceptibility axes of basalts from lower
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altitude (~535- 524m) on a NW-SE vertical plane.
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Figure GSA DR-2
Figure GSA DR-3
~560 m
~524-535 m
~520 m
Completely weathered basalt
~494 m
Lake water level
Figure GSA DR-4