Thermal-metamorphic signature of an impact event in the Vredefort dome, South Africa

Gibson, Roger L.; Reimold, W. U.; Stevens, Gary

doi:10.1130/0091-7613(1998)026<0787:tmsoai>2.3.co;2

Cited by 90 publications

(81 citation statements)

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“…Hydrothermal effects may have resulted in formation/ destruction of magnetic minerals and changes in grain size and domain state of magnetic carriers. Hydrothermal activity has been documented in impact craters (e.g., Allen et al 1982;Ames et al 1998;Gibson et al 1998). Detailed observations on magnetic mineralogy and hydrothermal minerals in the breccias are needed for interpretation of the paleomagnetic data.…”

Section: Discussionmentioning

confidence: 99%

Paleomagnetic and rock magnetic study of the Yaxcopoil‐1 impact breccia sequence, Chicxulub impact crater (Mexico)

Urrutia‐Fucugauchi

Soler-Arechalde

Rebolledo-Vieyra

et al. 2004

Meteorit & Planetary Scien

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Abstract-Results of a detailed paleomagnetic and rock magnetic study of samples of the impact breccia sequence cored in the Yaxcopoil-1 (Yax-1) borehole between about 800 m and 896 m are presented. The Yax-1 breccia sequence occurs from 794.63 m to 894.94 m and consists of redeposited melt-rich, clast-size sorted, fine-grained suevites; melt-rich, no clast-size sorting, medium-grained suevites; coarse suevitic melt agglomerates; coarse melt-rich heterogeneous suevites; brecciated suevites; and coarse carbonate and silicate melt suevites. The low-field susceptibility ranges from −0.3 to 4018 × 10 −6 SI, and the NRM intensity ranges from 0.02 mA/m up to 37510 mA/m. In general, the NRM intensity and magnetic susceptibility present wide ranges and are positively correlated, pointing to varying magnetic mineral contents and textures of the melt-rich breccia sequence. The vectorial composition and magnetic stability of NRM were investigated by both stepwise alternating field and thermal demagnetization. In most cases, characteristic single component magnetizations are observed. Both upward and downward inclinations are present through the sequence, and we interpret the reverse magnetization as the primary component in the breccias. Both the clasts and matrix forming the breccia appear to have been subjected to a wide range of temperature/pressure conditions and show distinct rock magnetic properties. An extended interval of remanence acquisition and secondary partial or total remagnetization may explain the paleomagnetic results.

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Section: Discussionmentioning

confidence: 99%

Paleomagnetic and rock magnetic study of the Yaxcopoil‐1 impact breccia sequence, Chicxulub impact crater (Mexico)

Urrutia‐Fucugauchi

Soler-Arechalde

Rebolledo-Vieyra

et al. 2004

Meteorit & Planetary Scien

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“…The Vredefort dome is ~80 km in diameter, and comprises a 40 km diameter Archean core of deep crustal rocks, surrounded by an annular collar of mid-crustal rocks [Gibson et al, 1998;Lana et al, 2003]. Hence, observations at both Sudbury and Vredefort suggest that there is a large amount of structural uplift in the central zone, and that the amount of structural uplift decreases outwards.…”

Section: Grieve and Pilkingtonmentioning

confidence: 99%

“…2b is inconsistent with observations at two similar-sized large terrestrial craters: Vredefort and Sudbury. The Vredefort dome is ~80 km wide, and comprises a 40 km diameter Archean core of deep crustal rocks surrounded by an annular collar of mid-crustal rocks [Gibson et al, 1998;Lana et al, 2003]. At Sudbury there is also a decrease in metamorphic grade with distance from the Sudbury Igneous Complex (SIC) [Riller, 2005;Grieve et al, 2008].…”

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confidence: 99%

Structural uplift beneath the Chicxulub impact structure

Vermeesch¹,

Morgan²

2008

J. Geophys. Res.

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Models of the central structure of large impact craters are poorly constrained, partly due to the lack of well-preserved terrestrial examples, and partly because of the extreme nature of impact events. Even large impact craters take only a few minutes to form, during which time rocks from the deep crust move upwards many kilometers, interacting with impact melts and breccias before settling to their final position. We construct a new model of central uplift beneath the Chicxulub crater, based upon a well-constrained 3D velocity model, obtained by jointly inverting seismic travel-time and gravity data. The input tomographic dataset has good resolution and many rays cross the central uplift in many directions. We use laboratory measurements to convert between velocity and density. Our velocity model possesses a highvelocity-zone near the crater center, and velocity gradually decreases outside this zone. We use regional refraction data to interpret these velocities in terms of a broad 80-km-wide zone of structural uplift, in which the central rocks originate from the lower crust, and the surrounding rocks from the mid and upper crust. This is in contrast with previous models in 2 2 which the zone of central uplift is either 40-50 km or 150 km wide. Our interpretation is consistent with: scaling laws, Yucatán basement lithology, other velocity data, observations at similar-sized terrestrial craters, and dynamic modeling of peak ring formation. Our model of the uplift at Chicxulub can be used to help distinguish between competing models of effective target strength in numerical models of crater formation.

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“…Erosion has removed the coherent impact-melt sheet and has been estimated to be in the range of 5 to 10 km (McCarthy et al 1990;Gibson et al 1998;Gibson and Reimold 2001). Kamo et al (1996) determined a U-Pb age from zircons in the granophyre and pseudotachylitic breccia of ~2020 Ma, which has been confirmed by more recent results, for the age of the Vredefort impact event.…”

Section: Vredefort South Africamentioning

confidence: 99%

“…They further suggested that the pervasive network of veins of pseudotachylitic breccia may have provided the means for large-scale continuous rock flow during structural uplift. The originally deepest rocks of the crystalline core of the Vredefort Dome are from mid-crustal levels (Lana et al 2003), and there is a progressive increase in recorded postimpact temperatures from ~300 °C in the outer collar rocks to >700 °C, and locally as high as 1000 °C, in the central core due to the geothermal gradient prior to impact-induced uplift and shock heating (Gibson et al 1998;Gibson 2002;Gibson and Reimold 2005). These high temperatures may have also assisted in mechanical strength degradation during structural uplift and modification.…”

Section: Vredefort South Africamentioning

confidence: 99%

Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formation

Grieve

Reimold

Morgan

et al. 2008

Meteorit & Planetary Scien

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Abstract-The structural, topographic and other characteristics of the Vredefort, Sudbury, and Chicxulub impact structures are described. Assuming that the structures originally had the same morphology, the observations/interpretations for each structure are compared and extended to the other structures. This does not result in any major inconsistencies but requires that the observations be scaled spatially. In the case of Vredefort and Sudbury, this is accomplished by scaling the outer limit of particular shock metamorphic features. In the case of Chicxulub, scaling requires a reasoned assumption as to the formation mechanism of an interior peak ring. The observations/interpretations are then used to construct an integrated, empirical kinematic model for a terrestrial peak-ring basin. The major attributes of the model include: a set of outward-directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor, some of which are pre-existing structures that have been reactivated during transient cavity formation; inward-directed motions along the same outermost structures and along a set of structures, at intermediate radial distances, during transient cavity collapse; structural uplift in the center followed by a final set of radially outward-directed thrusts at the outer edges of the structural uplift, during uplift collapse. The rock displacements on the intermediate, inward and innermost, outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift.

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Thermal-metamorphic signature of an impact event in the Vredefort dome, South Africa

Cited by 90 publications

References 0 publications

Paleomagnetic and rock magnetic study of the Yaxcopoil‐1 impact breccia sequence, Chicxulub impact crater (Mexico)

Paleomagnetic and rock magnetic study of the Yaxcopoil‐1 impact breccia sequence, Chicxulub impact crater (Mexico)

Structural uplift beneath the Chicxulub impact structure

Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formation

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