Magnetization on impact structures—Constraints from numerical modeling and petrophysics

Ugalde, Hernan; Artemieva, N.; Milkereit, B.

doi:10.1130/0-8137-2384-1.25

Cited by 24 publications

(28 citation statements)

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“…9). Recent integrated analysis of gravity and borehole petrophysical data and modeling has shown laterally varying physical properties at Bosumtwi, which are related to impact cratering processes (Ugalde et al 2005(Ugalde et al , 2007. Our reconstruction results (Fig.…”

Section: Reconstruction Of the Original Crater Reliefmentioning

confidence: 70%

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Post‐impact structural crater modification due to sediment loading: An overlooked process

Tsikalas

Faleide

2007

Meteorit & Planetary Scien

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Abstract-Post-impact crater morphology and structure modifications due to sediment loading are analyzed in detail and exemplified in five well-preserved impact craters: Mjølnir, Chesapeake Bay, Chicxulub, Montagnais, and Bosumtwi. The analysis demonstrates that the geometry and the structural and stratigraphic relations of post-impact strata provide information about the amplitude, the spatial distribution, and the mode of post-impact deformation. Reconstruction of the original morphology and structure for the Mjølnir, Chicxulub, and Bosumtwi craters demonstrates the long-term subsidence and differential compaction that takes place between the crater and the outside platform region, and laterally within the crater structure. At Mjølnir, the central high developed as a prominent feature during post-impact burial, the height of the peak ring was enhanced, and the cumulative throw on the rim faults was increased. The original Chicxulub crater exhibited considerably less prominent peakring and inner-ring/crater-rim features than the present crater. The original relief of the peak ring was on the order of 420-570 m (currently 535-575 m); the relief on the inner ring/crater rim was 300-450 m (currently ∼700 m). The original Bosumtwi crater exhibited a central uplift/high whose structural relief increased during burial (current height 101-110 m, in contrast to the original height of 85-110 m), whereas the surrounding western part of the annular trough was subdued more that the eastern part, exhibiting original depths of 43-68 m (currently 46 m) and 49-55 m (currently 50 m), respectively. Furthermore, a quantitative model for the porosity change caused by the Chesapeake Bay impact was developed utilizing the modeled density distribution. The model shows that, compared with the surrounding platform, the porosity increased immediately after impact up to 8.5% in the collapsed and brecciated crater center (currently +6% due to post-impact compaction). In contrast, porosity decreased by 2-3% (currently −3 to −4.5% due to post-impact compaction) in the peak-ring region. The lateral variations in porosity at Chesapeake Bay crater are compatible with similar porosity variations at Mjølnir crater, and are considered to be responsible for the moderate Chesapeake Bay gravity signature (annular low of −8 mGal instead of −15 mGal). The analysis shows that the reconstructions and the long-term alterations due to post-impact burial are closely related to the impact-disturbed target-rock volume and a brecciated region of laterally varying thickness and depthvarying physical properties. The study further shows that several crater morphological and structural parameters are prone to post-impact burial modification and are either exaggerated or subdued during post-impact burial. Preliminary correction factors are established based on the integrated reconstruction and post-impact deformation analysis. The crater morphological and structural parameters, corrected from post-impact loading and modification effects, can be used to better const...

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Section: Reconstruction Of the Original Crater Reliefmentioning

confidence: 70%

“…9) compacted relatively more, as it was underlain by a more porous impact breccia unit, whereas the central uplift/high and the eastern depression subsided relatively less, as they were underlain by less porous, melt-rich breccia related to structural uplift (Fig. 9) (Ugalde et al 2005(Ugalde et al , 2007.…”

Section: Reconstruction Of the Original Crater Reliefmentioning

confidence: 99%

Post‐impact structural crater modification due to sediment loading: An overlooked process

Tsikalas

Faleide

2007

Meteorit & Planetary Scien

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“…Previous estimations of the maximum shock pressure distribution within the Bosumtwi impact structure from numerical modeling can be used to predict the extent of fracturing and brecciation caused by the impact, related to the area where P > 1 GPa (Artemieva et al 2004;Ugalde et al 2005). Those results predicted fracturing across the entire crater, within a volume of ~5200 m radius (Artemieva et al 2004; Fig.…”

Section: Discussionmentioning

confidence: 99%

Integrated 3‐D model from gravity and petrophysical data at the Bosumtwi impact structure, Ghana

Ugalde

Danuor

Milkereit

2007

Meteorit & Planetary Scien

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Abstract-The Bosumtwi impact structure of central Ghana was drilled in 2004 as part of the International Continental Scientific Drilling Program (ICDP). A vast amount of geoscience data is available from the pre-site surveys and the actual drilling phase. A 3-D gravity model was constructed and calibrated with the available data from the two ICDP boreholes, LB-07A and LB-08A. The 3-D gravity model results agree well with both the sediment thickness and size of the central uplift revealed by previously collected seismic data, and with the petrophysical data from the LB-08A and LB-07A core materials and the two borehole logs. Furthermore, the model exhibits lateral density variations across the structure and refines the results from previous 2.5-D modeling. An important new element of the 3-D model is that the thickness of the intervals comprising polymict lithic impact breccia and suevite, monomict lithic breccia and fractured basement is much smaller than that predicted by numerical modeling.

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“…Under the present experimental conditions, the observed AMS changes were induced under estimated pressures of as low as 0.5 GPa. The results of numerical modeling predict that this pressure range covers relatively large volumes of target rocks beneath impact craters (e.g., Ugalde et al, 2005). Therefore, the application of AMS to known terrestrial impact structures would provide new insight into the process of impact-related cratering, while its application to suspected terrestrial impact structures would provide evidence of an impact origin.…”

Section: Summary and Discussionmentioning

confidence: 99%

Shock-induced anisotropy of magnetic susceptibility: impact experiment on basaltic andesite

2007

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Changes in the anisotropy of the low-field magnetic susceptibility (AMS) of basaltic andesite were induced by decaying stress waves and subsequently quantified. An initial shock pressure of 5 GPa was generated in a block of the target rock through impacting with a cylindrical projectile. Following the impact, the maximum or minimum principal susceptibility axes of the target were reoriented toward the shock direction at low (0.5-3 GPa) or high (>3 GPa) estimated shock pressures, respectively. Subtraction of the initial AMS demonstrated a parallelism between the induced susceptibility axes and the shock direction. These results suggest a potential application of AMS as an indicator of the propagation directions of stress waves generated in rocks at terrestrial impact structures.

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Magnetization on impact structures—Constraints from numerical modeling and petrophysics

Cited by 24 publications

References 0 publications

Post‐impact structural crater modification due to sediment loading: An overlooked process

Post‐impact structural crater modification due to sediment loading: An overlooked process

Integrated 3‐D model from gravity and petrophysical data at the Bosumtwi impact structure, Ghana

Shock-induced anisotropy of magnetic susceptibility: impact experiment on basaltic andesite

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