Petrographic studies of "fallout" suevite from outside the Bosumtwi impact structure, Ghana
Meteoritics and Planetary Science
Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Geological Survey Department, P.O. Box M80, Accra, Ghana
Field studies and a shallow drilling program carried out in 1999 provided information about thickness and distribution of suevite to the north of the Bosumtwi crater rim. Suevite occurrence there is known from an ∼1.5 km2 area; its thickness is ≤15 m. The present suevite distribution is likely the result of differential erosion and does not reflect the initial areal extent of continuous Bosumtwi ejecta deposits. Here we discuss the petrographic characteristics of drill core samples of melt-rich suevite. Macroscopic constituents of the suevites are melt bodies and crystalline and metasedimentary rock (granite, graywacke, phyllite, shale, schist, and possibly slate) clasts up to about 40 cm in size. Shock metamorphic effects in the clasts include multiple sets of planar deformation features (PDFs), diaplectic quartz and feldspar glasses, lechatelierite, and ballen quartz, besides biotite with kink bands. Basement rock clasts in the suevite represent all stages of shock metamorphism, ranging from samples without shock effects to completely shock-melted material that is indicative of shock pressures up to ∼60 GPa. © The Meteoritical Society, 2006.
crater; crystalline rock; ejecta; fallout; impact structure; metasedimentary rock; suevite; Africa; Ghana; Sub-Saharan Africa; West Africa