Shock Metamorphism of Bosumtwi Impact Crater Rocks, Shock Attenuation, and Uplift Formation

Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by ∼5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.

[1]  Falko Langenhorst,et al.  Shock metamorphism of quartz in nature and experiment: I. Basic observation and theory* , 1994 .

[2]  J. Ashby.  References and Notes , 1999 .

[3]  R. Grieve,et al.  Terrestrial Impact Structures , 1987 .

[4]  Mark J. Cintala,et al.  Scaling impact melting and crater dimensions: Implications for the lunar cratering record , 1998 .

[5]  B. Ivanov.  Numerical Modeling of the Largest Terrestrial Meteorite Craters , 2005 .

[6]  C. Koeberl,et al.  Lithostratigraphic and petrographic analysis of ICDP drill core LB‐07A, Bosumtwi impact structure, Ghana , 2007 .

[7]  W. Reimold,et al.  Experimental constraints on shock-induced microstructures in naturally deformed silicates , 1996 .

[8]  Christian Koeberl,et al.  Drill core LB‐08A, Bosumtwi impact structure, Ghana: Petrographic and shock metamorphic studies of material from the central uplift , 2007 .

[9]  R. Grieve,et al.  Microscopic planar deformation features in quartz of the Vredefort structure: Anomalous but still suggestive of an impact origin☆ , 1990 .

[10]  Elisabetta Pierazzo,et al.  A Reevaluation of Impact Melt Production , 1997 .

[11]  J. Overpeck,et al.  An international and multidisciplinary drilling project into a young complex impact structure: The 2004 ICDP Bosumtwi Crater Drilling Project—An overview , 2007 .

[12]  Bevan M. French,et al.  Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures , 1998 .

[13]  K. Brooks,et al.  Pronounced central uplift identified in the Bosumtwi impact structure, Ghana, using multichannel seismic reflection data , 2002 .

[14]  Virgil L. Sharpton,et al.  Shock metamorphism and shock barometry at a complex impact structure: Slate Islands, Canada , 1998 .

[15]  R. Grieve,et al.  Variations in shock deformation at the Slate Islands Impact Structure, Lake Superior, Canada , 1976 .

[16]  N. Mitani.  Numerical simulations of shock attenuation in solids and reevaluation of scaling law , 2003 .

[17]  Falko Langenhorst,et al.  Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience* , 1996 .