Anomalous quartz from the Roter Kamm impact crater, Namibia: Evidence for post-impact hydrothermal activity

Journal Article · Tue Aug 01 00:00:00 EDT 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90329-3· OSTI ID:7164105

Koeberl, C ^[1]; Fredriksson, K ^[2]; Goetzinger, M ^[3]; Reimold, W U ^[4]

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1. Lunar and Planetary Institute, Houston, TX (USA) Univ. of Vienna (Austria)
2. Smithsonian Institution, Washington, DC (USA)
3. Univ. of Vienna (Austria)
4. Univ. of the Witwatersrand, Johannesburg (South Africa)

Centimeter-sized quartz pebbles have been found on the rim of the Roter Kamm impact crater. The Roter Kamm crater has a diameter of about 2.5 km and is situated in the Namib Desert, SWA/Namibia. Because of the sand coverage, impact products are exposed exclusively in the form of ejecta on the crater rim. The quartz pebbles were found close to the main deposits of the impact breccias and show signs of wind abrasion. Thin sections revealed that the pebbles consist of individual quartz domains that are up to 1 mm in size. Under crossed nicols (polarized light), all individual domains show extinction almost simultaneously within {plus minus}2{degree}, which is a rare phenomenon. Microprobe studies, neutron activation analyses, and X-ray diffractometry confirmed that the material consists of pure quartz. The quartz contains three different types of fluid inclusions: primary inclusions that record the formation conditions of the quartz, very small (<1 {mu}m) secondary inclusions associated with the grain boundaries, and late inclusions of irregular size. Freezing point depression measurements of the primary inclusions indicate fluid salinities between 18.3 and 19.6 wt% NaCl. Homogenization temperatures (T{sub h}) for the primary inclusions range from 165 to 250{degree}C. The quartz and the primary inclusions may provide evidence for a post-impact phase of extensive hydrothermal activity, generated by the residual heat from the kinetic energy of the impact.

• OSTI ID: 7164105
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:8; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
INCLUSIONS
CHEMICAL COMPOSITION
METEORITES
IMPACT SHOCK
QUARTZ
PETROGRAPHY
ACTIVATION ANALYSIS
GEOCHEMISTRY
GEOTHERMOMETRY
HYDROTHERMAL ALTERATION
MICROANALYSIS
NAMIBIA
SALINITY
X-RAY DIFFRACTION
AFRICA
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMISTRY
COHERENT SCATTERING
DIFFRACTION
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SCATTERING
SILICON COMPOUNDS
SILICON OXIDES
580000* - Geosciences