Pseudotachylite vein hosted by a clast in the Vredefort Granophyre: characterization, origin and relevance

Kovaleva, Elizaveta; Huber, M. S.; Roelofse, Frederick; Tredoux, M.; Praekelt, H.E.

doi:10.25131/sajg.121.0002

Cited by 14 publications

(13 citation statements)

References 51 publications

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“…(), as well as where a granitic fragment with a pseudotachylite vein was discovered within the granophyre, indicating that the generation of the pseudotachylite preceded the emplacement of the granophyre dykes (Kovaleva et al. 2018b). Another recent study showed a relatively high abundance of inhomogeneously distributed clasts within the dyke (Kovaleva et al.…”

Section: Introductionmentioning

confidence: 99%

Geophysical characterization of the Daskop granophyre dyke and surrounding host rocks, Vredefort impact structure, South Africa

Fourie

Huber

Kovaleva

2019

Meteorit & Planetary Scien

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Granophyre dykes in the central part of the Vredefort impact structure are believed to be the remnants of the impact melt sheet, which intruded downwards along the fractures in the crater floor. Little is known about their original penetration depth, dip, structural relationships with the host rocks, and their general geophysical characteristics. This information is critical to understand the emplacement history of the granophyre dykes, as it relates to the formation and modification of large impact structures. We conducted magnetic and resistivity surveys across the Daskop granophyre dyke (DGD), one of the impact melt dykes in the structure's core. The magnetic survey revealed that the DGD gives a strong magnetic response at positions where the dyke outcrop exceeds the surface topography, but a very weak response where the outcrop is nearly at the same elevation as the surrounding topography. The magnetic anomaly is thus predominantly due to the outcrop protruding above ground level, suggesting a limited volume of dyke material in the subsurface and a small penetration depth. The resistivity survey performed on two profiles, set perpendicularly across the DGD, indicated a shallow penetration depth (<3 m), consistent with the magnetic interpretation. Thus, our geophysical study demonstrates that the DGD is currently at the very bottom of its original emplacement. This may either be an erosional coincidence, or it may be controlled by a fundamental process of impact cratering. Further studies are warranted to determine if other granophyre dykes at Vredefort are similarly at their lowermost terminations.

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Section: Introductionmentioning

confidence: 99%

Geophysical characterization of the Daskop granophyre dyke and surrounding host rocks, Vredefort impact structure, South Africa

Fourie

Huber

Kovaleva

2019

Meteorit & Planetary Scien

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“…It is a small meta-granite clast with a sharply crosscutting vein ( Figure 1B). Preliminary petrological and geochemical analyses of this clast were presented in [20]. It was shown geochemically and petrographically that the vein has a granitic affinity, rather than being an offshoot of a granophyre within the inclusion [20].…”

Section: The Vredefort Impact Structure: Geological Settingmentioning

confidence: 98%

“…Since the impact event, the impact structure has been eroded to a depth of 8-10 km [13,14]. [20]. The granophyre matrix (brown) contains multiple lithic clasts (light-grey).…”

Section: The Vredefort Impact Structure: Geological Settingmentioning

confidence: 99%

“…Kovaleva et al [20] described one such clast, enclosed in granophyre and containing a thin pseudotachylite (PT) vein. At that time, however, doubts about the origin of the PT vein existed.…”

Section: Introductionmentioning

confidence: 99%

“…At that time, however, doubts about the origin of the PT vein existed. Considering the long tectonic history of the area, this PT vein could be interpreted to have a pre-impact, tectonic origin, or an impact-related origin [20,21]. The small sample size and the high degree of alteration make it difficult to perform isotopic dating on the PT vein in question.…”

Section: Introductionmentioning

confidence: 99%

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Properties of Impact-Related Pseudotachylite and Associated Shocked Zircon and Monazite in the Upper Levels of a Large Impact Basin: a Case Study From the Vredefort Impact Structure

Kovaleva

Dixon

2020

Minerals

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The Vredefort impact structure in South Africa is deeply eroded to its lowermost levels. However, granophyre (impact melt) dykes in such structures preserve clasts of supracrustal rocks, transported down from the uppermost levels of the initial structure. Studying these clasts is the only way to understand the properties of already eroded impactites. One such lithic clast from the Vredefort impact structure contains a thin pseudotachylite vein and is shown to be derived from the near-surface environment of the impact crater. Traditionally, impact pseudotachylites are referred to as in situ melt rocks with the same chemical and isotopic composition as their host rocks. The composition of the sampled pseudotachylite vein is not identical to its host rock, as shown by the micro-X-ray fluorescence (µXRF) and energy-dispersive X-ray (EDX) spectrometry mapping. Mapping shows that the melt transfer and material mixing within pseudotachylites may have commonly occurred at the upper levels of the structure. The vein is spatially related to shocked zircon and monazite crystals in the sample. Granular zircons with small granules are concentrated within and around the vein (not farther than 6–7 mm from the vein). Zircons with planar fractures and shock microtwins occur farther from the vein (6–12 mm). Zircons with microtwins (65°/{112}) are also found inside the vein, and twinned monazite (180°/[101]) is found very close to the vein. These spatial relationships point to elevated shock pressure and shear stress, concentrated along the vein’s plane during impact.

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Nano-scale investigation of granular neoblastic zircon, Vredefort impact structure, South Africa: Evidence for complete shock melting

Kovaleva

Kusiak

Kenny

et al. 2021

Earth and Planetary Science Letters

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Pseudotachylite vein hosted by a clast in the Vredefort Granophyre: characterization, origin and relevance

Cited by 14 publications

References 51 publications

Geophysical characterization of the Daskop granophyre dyke and surrounding host rocks, Vredefort impact structure, South Africa

Geophysical characterization of the Daskop granophyre dyke and surrounding host rocks, Vredefort impact structure, South Africa

Properties of Impact-Related Pseudotachylite and Associated Shocked Zircon and Monazite in the Upper Levels of a Large Impact Basin: a Case Study From the Vredefort Impact Structure

Nano-scale investigation of granular neoblastic zircon, Vredefort impact structure, South Africa: Evidence for complete shock melting

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