Impact Structure

14,000,000 Leading Edge Experts on the ideXlab platform

Scan Science and Technology

Contact Leading Edge Experts & Companies

Scan Science and Technology

Contact Leading Edge Experts & Companies

The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

Wolf Uwe Reimold - One of the best experts on this subject based on the ideXlab platform.

  • Bosumtwi Impact Structure, Ghana: Evidence for fluidized emplacement of the ejecta
    Meteoritics and Planetary Science, 2018
    Co-Authors: David Baratoux, Wolf Uwe Reimold, Cheikh Ahmadou Bamba Niang, Marian Selorm Sapah, Mark Walter Jessell, Daniel Boamah, Gayane Faye, Sylvain Bouley, Olivier Vanderhaeghe
    Abstract:

    The about 10.5 km diameter Bosumtwi Impact crater is one of the youngest large Impact Structures on Earth. The crater rim is readily noticed on topographic maps or in satellite imagery. It defines a circular basin filled by water (Lake Bosumtwi) and lacustrine sediments. The morphology of this Impact Structure is also characterized by a circular plateau extending beyond the rim and up to 9-10 km from the center of the crater (about 2 crater radii). This feature comprises a shallow ring depression, also described as an annular moat, and a subdued circular ridge at its outer edge. The origin of this outermost feature could so far not be elucidated based on remote sensing data only. Our approach combines detailed topographic analysis, including roughness mapping, with airborne radiometric surveys (mapping near-surface K, Th, U concentrations) and field observations. This provides evidence that the moat and outer ring are features inherited from the Impact event and represent the partially eroded ejecta layer of the Bosumtwi Impact Structure. The characteristics of the outer ridge indicate that ejecta emplacement was not purely ballistic but requires ejecta fluidization and surface flow. The setting of Bosumtwi ejecta can therefore be considered as a terrestrial analog for rampart craters, which are common on Mars and Venus, and also found on icy bodies of the outer solar system (e.g., Ganymede, Europa, Dione, Tethys, and Charon). Future studies at Bosumtwi may therefore help to elucidate the mechanism of formation of rampart craters.

  • Geological investigation of the central portion of the Santa Marta Impact Structure, Piauí State, Brazil
    2017
    Co-Authors: Grace Juliana Gonçalves De Oliveira, Marcos Alberto Rodrigues Vasconcelos, Alvaro Penteado Crósta, Ana Maria Góes, Marlei Antônio Carrari Chamani, Wolf Uwe Reimold
    Abstract:

    ABSTRACT: Santa Marta is a 10 km wide, reasonably well preserved, complex Impact Structure located in southwestern Piauí state, northeastern Brazil, with a central uplift of 3.2 km diameter. The Santa Marta Structure was recently recognized as the sixth confirmed Impact Structure in Brazil, based on widespread occurrence of shatter cones and the presence of shock deformation features in quartz. The latter includes planar deformation features (PDF), planar fractures (PF), and feather features (FF). The Structure was formed in sedimentary strata (conglomerates, sandstones, siltstones and shales) accumulated in two distinct sedimentary basins that overlap in this region: the Paleozoic Parnaíba and the Mesozoic Sanfranciscan basins. Here, we provide an overview of the geology and stratigraphy of the sedimentary successions that occur within the Structure, focusing especially on the deformation aspects of the strata from the central area. This study is aimed at advancing the knowledge about Brazilian Impact Structures and contributing to a better comprehension of Impact cratering in sedimentary targets. The deformation in the Santa Marta Structure is directly related to variations in the thickness of sedimentary strata and to lithologic diversity in the interior of the Structure, which determined the complexity of the deformation, including the formation of inner rings.

  • Shatter cones at the Keurusselkä Impact Structure and their relation to local jointing
    Meteoritics & Planetary Science, 2016
    Co-Authors: Maximilian Hasch, Wolf Uwe Reimold, Ulli Raschke, Patrice Tristan Zaag
    Abstract:

    Shatter cones are the only distinct meso- to macroscopic recognition criterion for Impact Structures, yet not all is known about their formation. The Keurusselka Impact Structure, Finland, is interesting in that it presents a multitude of well-exposed shatter cones in medium- to coarse-grained granitoids. The allegedly 27 km wide Keurusselka Impact Structure was formed about 1150 Ma ago in rocks of the Central Finland Granitoid Complex. Special attention was paid in this work to possible relationships between shatter cones and local, as well as regionally occurring, fracture or joint systems. A possible shatter cone find outside the previously suggested edge of the Structure could mean that the Keurusselka Impact Structure is larger than previously thought. The spacing between joints/fractures from regional joint systems was influenced by the Impact, but Impact-induced fractures strongly follow the regional joint orientation trends. There is a distinct relationship between shatter cones and joints: shatter cones occur on and against joint surfaces of varied orientations and belonging to the regional orientation trends. Planar fractures (PF) and planar deformation features (PDF) were found in three shatter cone samples from the central-most part of the Impact Structure, whereas other country rock samples from the same level of exposure but further from the assumed center lack shock deformation features. PDF occurrence is enhanced within 5 mm of shatter cone surfaces, which is interpreted to suggest that shock wave reverberation at preImpact joints could be responsible for this local enhancement of shock deformation. Some shatter cone surfaces are coated with a quasi-opaque material which is also found in conspicuous veinlets that branch off from shatter cone surfaces and resemble pseudotachylitic breccia veins. The vein-filling is composed of two mineral phases, one of which could be identified as a montmorillonitic phyllosilicate. The second phase could not be identified yet. The original composition of the fill could not be determined. Further work is required on this material. Observed joints and fractures were discussed against findings from Barringer Impact crater. They show that Impact-induced joints in the basement rock do not follow Impact-specific orientations (such as radial, conical, or concentric).

  • The Serra da Cangalha Impact Structure, Brazil: Geological, stratigraphic and petrographic aspects of a recently confirmed Impact Structure
    Journal of South American Earth Sciences, 2013
    Co-Authors: Marcos Alberto Rodrigues Vasconcelos, Wolf Uwe Reimold, Alvaro Penteado Crósta, Ana Maria Góes, Thomas Kenkmann, Michael H. Poelchau
    Abstract:

    Abstract Serra da Cangalha is a complex Impact Structure with an apparent diameter of 13.7 km located in essentially undisturbed sedimentary rocks of the Parnaiba basin in northeastern Brazil. The stratigraphy of the crater region includes, from bottom to top, the Longa, Poti, Piaui and Pedra de Fogo formations of Devonian to Late Permian age. The age of the Impact event is constrained to

  • Vredefort: The Largest and Oldest Impact Structure in the World
    Meteorite Impact!, 2010
    Co-Authors: Wolf Uwe Reimold, Roger L. Gibson
    Abstract:

    Th e Vredefort Impact Structure is enormous! In fact, it is so big (hundreds of kilometres in diameter) that it is not as readily revealed to the casual visitor as much smaller craters such as Tswaing (Fig. 48).

C. Champollion - One of the best experts on this subject based on the ideXlab platform.

  • Geophysical signature of the Tunnunik Impact Structure, Northwest Territories, Canada
    Meteoritics and Planetary Science, 2020
    Co-Authors: Y. Quesnel, Camille Lepaulard, Jerome Gattacceca, W. Zylberman, P. Rochette, Minoru Uehara, G. Osinski, P. Dussouillez, C. Champollion
    Abstract:

    In 2011, the discovery of shatter cones confirmed the 28 km-diameter Tunnunik complex Impact Structure, Northwest Territories, Canada. This study presents the first results of ground-based electromagnetic, gravimetric and magnetic surveys over this Impact Structure. Its central area is characterized by a ~10 km wide negative gravity anomaly of about 3 mGal amplitude, roughly corresponding to the area of shatter cones, and associated with a positive magnetic field anomaly of ~120 nT amplitude and 3 km wavelength. The latter correlates well with the location of the deepest uplifted strata, an Impact-tilted Proterozoic dolomite layer of the Shaler Supergroup exposed near the center of the Structure and intruded by dolerite dykes. Locally, electromagnetic field data unveil a conductive superficial formation which corresponds to an 80-100 m thick sand layer covering the Impact Structure. Based on measurements of magnetic properties of rock samples, we model the source of the magnetic anomaly as the magnetic sediments of the Shaler Supergroup combined with a core of uplifted crystalline basement with enhanced magnetization. More classically, the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations. However, the present-day fractured zone does not extend deeper than ~1 km in our model, indicating a possible 1.5 km of erosion since the time of Impact, about 430 Ma ago.

Jerome Gattacceca - One of the best experts on this subject based on the ideXlab platform.

  • Geophysical signature of the Tunnunik Impact Structure, Northwest Territories, Canada
    Meteoritics and Planetary Science, 2020
    Co-Authors: Y. Quesnel, Camille Lepaulard, Jerome Gattacceca, W. Zylberman, P. Rochette, Minoru Uehara, G. Osinski, P. Dussouillez, C. Champollion
    Abstract:

    In 2011, the discovery of shatter cones confirmed the 28 km-diameter Tunnunik complex Impact Structure, Northwest Territories, Canada. This study presents the first results of ground-based electromagnetic, gravimetric and magnetic surveys over this Impact Structure. Its central area is characterized by a ~10 km wide negative gravity anomaly of about 3 mGal amplitude, roughly corresponding to the area of shatter cones, and associated with a positive magnetic field anomaly of ~120 nT amplitude and 3 km wavelength. The latter correlates well with the location of the deepest uplifted strata, an Impact-tilted Proterozoic dolomite layer of the Shaler Supergroup exposed near the center of the Structure and intruded by dolerite dykes. Locally, electromagnetic field data unveil a conductive superficial formation which corresponds to an 80-100 m thick sand layer covering the Impact Structure. Based on measurements of magnetic properties of rock samples, we model the source of the magnetic anomaly as the magnetic sediments of the Shaler Supergroup combined with a core of uplifted crystalline basement with enhanced magnetization. More classically, the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations. However, the present-day fractured zone does not extend deeper than ~1 km in our model, indicating a possible 1.5 km of erosion since the time of Impact, about 430 Ma ago.

  • A Paleozoic age for the Tunnunik Impact Structure
    Meteoritics and Planetary Science, 2019
    Co-Authors: Camille Lepaulard, Jerome Gattacceca, Nicholas Swanson-hysell, Yoann Quesnel, François Demory, Gordon Osinski
    Abstract:

    We report paleomagnetic directions from the target rocks of the Tunnunik Impact Structure, as well as from lithic Impact breccia dikes that formed during the Impact event. The target sedimentary rocks have been remagnetized after Impact-related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 degrees C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 degrees C. The Impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting virtual geomagnetic pole for the Tunnunik Impact Structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an Impact age in the Late Ordovician or Silurian, around 430-450 Ma, soon after the deposition of the youngest Impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postImpact temperature of the studied rocks was about 350 degrees C.

  • Hydrothermally enhanced magnetization at the center of the Haughton Impact Structure?
    Meteoritics and Planetary Science, 2017
    Co-Authors: W. Zylberman, Yoann Quesnel, Gordon R. Osinski, Pierre Rochette, Cassandra Marion, Jerome Gattacceca
    Abstract:

    Haughton is a ~24 Myr old mid-size (apparent diameter 23 km) complex Impact Structure located on Devon Island in Nunavut, Canada. The center of the Structure shows a negative gravity anomaly of -12 mgal coupled to a localized positive magnetic field anomaly of ~900 nT. A field expedition in 2013 led to the acquisition of new ground magnetic field mapping and electrical resistivity datasets, as well as the first subsurface drill cores down to 13 m depth at the top of the magnetic field anomaly. Petrography, rock magnetic and petrophysical measurements were performed on the cores and revealed two different types of clast-rich polymict Impactites: (1) a white hydrothermally-altered Impact breccia, not previously observed at Haughton, and (2) a grey Impact breccia with no macroscopic sign of alteration. In the altered core, gypsum is present in macroscopic veins and in the form of intergranular selenite associated with colored and zoned carbonate clasts. This altered core has a natural remanent magnetization (NRM) four to five times higher than materials from the other core but the same magnetic susceptibility. Their magnetization is still higher than the surrounding crater-fill Impact melt rocks. X-ray Fluorescence data indicate a similar proportion of iron-rich phases in both cores and an enrichment in silicates within the altered core. In addition, alternating-field demagnetization results show that one main process remagnetized the rocks. These results support the hypothesis that intense and possibly localized post-Impact hydrothermal alteration enhanced the magnetization of the clast-rich Impact melt rocks by crystallization of magnetite within the center of the Haughton Impact Structure. Subsequent erosion was followed by in-situ concentration in the subsurface leading to large magnetic gradient on surface.

Camille Lepaulard - One of the best experts on this subject based on the ideXlab platform.

  • Geophysical signature of the Tunnunik Impact Structure, Northwest Territories, Canada
    Meteoritics and Planetary Science, 2020
    Co-Authors: Y. Quesnel, Camille Lepaulard, Jerome Gattacceca, W. Zylberman, P. Rochette, Minoru Uehara, G. Osinski, P. Dussouillez, C. Champollion
    Abstract:

    In 2011, the discovery of shatter cones confirmed the 28 km-diameter Tunnunik complex Impact Structure, Northwest Territories, Canada. This study presents the first results of ground-based electromagnetic, gravimetric and magnetic surveys over this Impact Structure. Its central area is characterized by a ~10 km wide negative gravity anomaly of about 3 mGal amplitude, roughly corresponding to the area of shatter cones, and associated with a positive magnetic field anomaly of ~120 nT amplitude and 3 km wavelength. The latter correlates well with the location of the deepest uplifted strata, an Impact-tilted Proterozoic dolomite layer of the Shaler Supergroup exposed near the center of the Structure and intruded by dolerite dykes. Locally, electromagnetic field data unveil a conductive superficial formation which corresponds to an 80-100 m thick sand layer covering the Impact Structure. Based on measurements of magnetic properties of rock samples, we model the source of the magnetic anomaly as the magnetic sediments of the Shaler Supergroup combined with a core of uplifted crystalline basement with enhanced magnetization. More classically, the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations. However, the present-day fractured zone does not extend deeper than ~1 km in our model, indicating a possible 1.5 km of erosion since the time of Impact, about 430 Ma ago.

  • A Paleozoic age for the Tunnunik Impact Structure
    Meteoritics and Planetary Science, 2019
    Co-Authors: Camille Lepaulard, Jerome Gattacceca, Nicholas Swanson-hysell, Yoann Quesnel, François Demory, Gordon Osinski
    Abstract:

    We report paleomagnetic directions from the target rocks of the Tunnunik Impact Structure, as well as from lithic Impact breccia dikes that formed during the Impact event. The target sedimentary rocks have been remagnetized after Impact-related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 degrees C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 degrees C. The Impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting virtual geomagnetic pole for the Tunnunik Impact Structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an Impact age in the Late Ordovician or Silurian, around 430-450 Ma, soon after the deposition of the youngest Impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postImpact temperature of the studied rocks was about 350 degrees C.

Deepak Srivastava - One of the best experts on this subject based on the ideXlab platform.

  • alternating augite plagioclase wedges in basement dolerites of lockne Impact Structure sweden a new shock wave induced deformation feature
    Meteoritics & Planetary Science, 2017
    Co-Authors: Boris Reznik, Amar Agarwal, Luis M Alvavaldivia, Deepak Srivastava
    Abstract:

    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.

  • Alternating augite‐plagioclase wedges in basement dolerites of Lockne Impact Structure, Sweden: A new shock wave‐induced deformation feature
    Meteoritics & Planetary Science, 2016
    Co-Authors: Amar Agarwal, Boris Reznik, Luis M. Alva-valdivia, Deepak Srivastava
    Abstract:

    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.