Relationships among magnetic fabrics, microfractures and shock pressures at an impact crater: A case study from Lockne crater, Sweden

Agarwal, Amar; Kontny, Agnes; Greiling, Reinhard O.

doi:10.1016/j.jappgeo.2015.01.010

Cited by 21 publications

(17 citation statements)

References 60 publications

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“…Similar distribution of impact-generated fractures is also reported from other natural impact craters, e.g., Meteor crater, United States, and Lockne crater , Sweden (Kumar and Kring, 2008;Agarwal et al, 2015).…”

Section: Origin Of Microfracturessupporting

confidence: 80%

“…In some microcraters, the radial microfractures postdate the concentric microfractures, while in others, the radial microfractures predate the concentric microfractures. The overprinting relationship between the radial and concentric fractures is a useful indicator of their genetic relationship (e.g., Graham et al, 2004;Agarwal et al, 2015). In the Lonar crater, the radial microfractures are older than the concentric microfractures.…”

Section: Origin Of Microfracturesmentioning

confidence: 99%

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Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Agarwal

Kontny

Srivastava

et al. 2015

Geological Society of America Bulletin

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The study of shock pressure indicators can provide important clues for understanding the cratering process, though the estimation of shock pressures in weakly shocked rocks is commonly difficult. In this study, we selected a very young and well-preserved impact structure, the Lonar crater in India. The crater, devoid of any tectonic overprint, can be assumed as pristine. We used a combination of rock magnetic and microfracture studies to estimate shock pressure in the crater rim. On the basis of present results, the magnetic fabrics are interpreted to be of magmatic origin related to the Deccan basalt emplacement. The high-coercivity component of the natural remnant magnetization in the crater rim basalt is similar to that in the unshocked basalt. The lack of any shock-related magnetic overprint on the crater rim basalt is, therefore, evident in the Lonar crater.In contrast, radial and concentric microfractures observed in basalts at the crater rim and farther away show symmetric distribution with respect to the crater. The concentric microfractures consistently overprint the radial microfractures. We infer that the radial and concentric microfractures were developed during propagation of the early compressional and the late decompressional shock wave components, respectively. The results of our rock magnetic and microfracture studies, when interpreted in light of published experimental and numerical simulation studies on the Lonar basalt, reveal that the shock pressure in the Lonar crater rim was less than 0.5 GPa but greater than 0.2 GPa. This shock pressure was high enough to produce fractures but too low to affect the magnetic fabrics. These results give new information on the relationship between shock pressure and resulting microfractures.

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Section: Origin Of Microfracturessupporting

confidence: 80%

Section: Origin Of Microfracturesmentioning

confidence: 99%

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Agarwal

Kontny

Srivastava

et al. 2015

Geological Society of America Bulletin

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“…AMS of magnetic fabric is already an established technique for understanding impact processes, especially at low peak shock pressures (0.5 to 3 GPa), at which other common shock indicators are rare (e.g., Agarwal et al, ; Agarwal, Kontny, Srivastava, & Greiling, ; Misra et al, ; Stöffler et al, ). The present study concludes that folding and kinking of biotite due to shock deformation may cause a significant reorientation of magnetic fabrics by passively changing the position of magnetite grains with respect to each other.…”

Section: Discussionmentioning

confidence: 99%

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

et al. 2019

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Magnetic fabrics provide important clues for understanding impact cratering processes. However, only a few magnetic fabric studies for experimentally shocked material have been reported so far. In the framework of MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network), we conducted two impact experiments on blocks of Maggia gneiss with the foliation oriented perpendicular (A38) and parallel (A37) to the target surface. Maggia gneiss has plenty of biotite bands forming a strong rock foliation. The bulk magnetic susceptibility varies from 0.376 × 10−3 to 1.298 × 10−3 SI in unshocked and from 0.443 × 10−3 to 3.940 × 10−3 SI in shocked gneiss. The thermomagnetic curves reveal a Verwey transition at −147 °C and a Curie temperature between 576 and 579 °C in unshocked and shocked samples, indicating nearly pure magnetite, which carries the magnetic fabrics. In A37 and A38 kinking is prominent from the point source down to a depth of 2 and 4.2 dp (projectile diameter) or 1 and 2.1 cm, respectively. Kinking, folding, and fracturing changed the position of magnetite grains with respect to each other to reorient the magnetic fabrics. Reorientation of magnetic fabrics is conspicuous down to 20 dp (10 cm) in A38, where no other impact‐related deformation is visible. The reorientation of magnetic fabrics may, therefore, aid in identifying impact processes at very low pressures, starting at 0.1 GPa, when other common indicators are absent.

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“…All samples show conspicuous radial and concentric microfractures (Agarwal et al. ). The radial microfractures form parallel with the direction of shock wave propagation and the maximum compression direction, while the concentric microfractures form perpendicular to the shock wave propagation direction and parallel with the direction of minimum compression.…”

Section: Methodsmentioning

confidence: 99%

“…The dolerites show shock wave‐generated radial and concentric fractures but have not suffered pre‐ or postimpact tectonic deformation (Agarwal et al. ). Agarwal et al.…”

Section: Introductionmentioning

confidence: 99%

Alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden: A new shock wave‐induced deformation feature

Agarwal

Резник

Alva‐Valdivia

et al. 2016

Meteorit & Planetary Scien

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This paper reports peculiar alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden. The combined microscopic and spectroscopic studies of the micro/nanoscale wedges reveal that these are deformation‐induced features. First, samples showing wedges, 12 out of 18 studied, are distributed in the impact structure within a radius of up to 10 km from the crater center. Second, the margins between the augite and labradorite wedges are sharp and the {110} prismatic cleavage of augite develops into fractures and thereafter into wedges. The fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain. Third, compared to the bulk labradorite, the dislocation density and the residual strain in the labradorite wedges are significantly higher. A possible mechanism of genesis of the wedges is proposed. The mechanism explains that passing of the shock waves in the basement dolerite induced (i) formation of microfractures in augite and labradorite; (ii) development of the augite prismatic cleavages into the wedges, which overprint the microfracture in the labradorite wedges; and (iii) thereafter, infilling of microfractures in the augite wedges by labradorite.

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Relationships among magnetic fabrics, microfractures and shock pressures at an impact crater: A case study from Lockne crater, Sweden

Cited by 21 publications

References 60 publications

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

Alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden: A new shock wave‐induced deformation feature

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