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A new locality of in situ massive impact-melt rock was discovered on the south-southwestern rim of the Roter Kamm impact structure. While the sub-samples from this new locality are relatively homogeneous at the hand specimen scale, and despite being from a nearby location, they do not have the same composition of the only previously analyzed impact-melt rock sample from Roter Kamm. Both Roter Kamm impact-melt rock samples analyzed to date, as well as several suevite samples, exhibit a granitic-granodioritic precursor composition. Micro-chemical analyses of glassy matrix and Al-rich orthopyroxene microphenocrysts demonstrate rapid cooling and chemical disequilibrium at small scales. Platinum-group element abundances and ratios indicate an ordinary chondritic composition for the Roter Kamm impactor. Laser argon dating of two sub-samples did not reproduce the previously obtained age of 3.7 for this impact event, based on 40Ar39Ar dating of a single vesicular impact-melt rock. Instead, we obtained ages between 3.9 and 6.3 Ma, with an inverse isochron age of 4.7 Ma for one analyzed sub-sample and 5.1 Ma for the other. Clearly a post-5 Ma impact at Roter Kamm remains indicated, but further analytical work is required to better constrain the currently best estimate of 4-5 Ma. Both impactor and age constraints are clearly obstructed by the inherent microscopic heterogeneity and disequilibrium melting and cooling processes demonstrated in the present study.
Originele taal-2 | English |
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Pagina's (van-tot) | 1201-1218 |
Aantal pagina's | 18 |
Tijdschrift | Meteoritics & Planetary Science |
Volume | 43 |
Status | Published - 2008 |
Bibliografische nota
Meteoritical SocietyVingerafdruk
Duik in de onderzoeksthema's van 'New impact-melt rock from the Roter Kamm impact structure, Namibia: Further constraints on impact age, melt rock chemistry, and projectile composition'. Samen vormen ze een unieke vingerafdruk.Projecten
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FWOAL378: Methodeontwikkeling voor interdisciplinair isotopisch onderzoek middels multicollector ICP-massaspectrometrie.
Claeys, P., Goderis, S. & Claeys, P.
1/01/06 → 31/12/09
Project: Fundamenteel