Incipient devitrification of impact melt particles at Bosumtwi crater, Ghana: Implications for suevite cooling history and melt dispersion

1Rudolf Välja, 1Kalle Kirsimäe, 2,3Christian Köeberl, 4Daniel Boamah, 1Juho Kirs
Meteoritics & Plantary Science (in Press) Link to Article []
1Department of Geology, University of Tartu, , 50411 Tartu, Estonia
2Department of Lithospheric Research, University of Vienna, , 1090 Vienna, Austria
3Natural History Museum, , 1010 Vienna, Austria
4Ghana Geological Survey Department, , Accra, Ghana
Published by arrangement with John Wiley & Sons

The petrographic, mineralogical, and geochemical compositions of the incipient devitrification products in impact melt fragments found in outer suevites at the Bosumtwi impact crater were studied to reconstruct the postimpact environmental constraints on the suevite formation and to refine its cooling history. Our study shows that devitrified melt/particles contain numerous microlitic crystals and crystal aggregates of different shapes derived from rapid cooling. The matrix of melt/particles in Bosumtwi suevites contains abundant Mg‐hercynite (pleonaste)‐type spinels with sizes rarely exceeding a few micrometers. High nucleation density of microlites suggests rapid crystallization under strong undercooling in the presence of abundant volatiles. Although the Bosumtwi impact event took place in a continental environment, the possible sources for elevated fluid/volatile content could have been the groundwater in the deeply weathered and fractured‐jointed Birimian basement, dewatering of abundant hydrous phases in weathered crust or hydrothermally altered basement, and the shale/phyllite–greywacke lithologies in the target rocks. Our results show that enough volatiles were present in the target rocks at the time of impact for the effective impact melt dispersion observed in Bosumtwi impactites.


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