Paper No. 86-10
Presentation Time: 10:30 AM
LITHOLOGICAL AND STRUCTURAL CHARACTERISTICS OF BOSUMTWI CRATER, GHANA
Lake Bosumtwi is a natural inland freshwater lake that originated from a meteorite impact. It is the largest natural lake in West Africa, located about 30 km South-East of Kumasi, the regional capital of the Ashanti Region of Ghana. It is centered at 06°32’N and 01°25’W with a diameter of about 10.5 km and 78 m depth. The Bosumtwi impact crater is formed in the 2.1-2.2 Ga Precambrian Metasedimentary and Metavolcanic rocks that are intruded by various crystalline rocks, predominantly bodies (dykes, veins) of granitic-dioritic composition. The supracrustal rocks comprise more or less tightly interbedded Phyllites, mica Schists, meta-tuffs, and meta-greywackes, Quartzite, Shales and Greenstones. This report details the geological map and the structural orientations and analysis of the major geologic units of the lake Bosumtwi area. Strike/dip measurements of the major structures/geologic units were undertaken in the area over a 6 week period. Rock samples from the major geologic units were taken to the lab for chemical and petrographic analysis. The general striking of most outcrops measured followed the NE-SW trend, as expected of the Birimian supergroup. Averagely, the dip angle of rock units at the Lake Bosumtwi area are 50º towards the SE and 70º towards the SW. Structural features such as microfaults, microfolds and joints were observed within outcrops and along road cuts. The presence of Suevite (polymict lithic impact breccia) at the Bosumtwi area as well as the major irregularities in outcrops, reaffirms the hypothesis surrounding the formation of the crater.