Abstract-The 1.07 Myr old Lake Bosumtwi impact crater in Ghana was drilled within the framework of the International Continental Scientific Drilling Project (ICDP). Hole LB-08A, drilled into the outer flank of the central uplift and with a total depth of 451 m, yielded 215.71 m of impact-related rocks. This paper summarizes observations of the lithological logging on core LB-08A. Between a depth of 235.6 and ~260 m, the section consists of a melt-bearing allochthonous, polymict, and mostly clast-supported impact breccia. Down to ~418 m, the section comprises a rather uniform unit of metagraywacke alternating with phyllite to slate (lower greenschist facies); few (par-) autochthonous impact breccia bodies and rare impact dike breccias are present. The lowermost part of the section contains several centimeter-to decimeter-thick melt-bearing breccia dikes in country rocks identical to those occurring above. Omnipresent fracturing was mapped in a qualitative manner. Most prominent shock effects in the uplifted target rocks comprise planar fractures and deformation elements in quartz and polysynthetic twinning in carbonate minerals; the maximum shock pressure as evidenced by quartz is below 26 GPa. The allochthonous breccias occasionally contain a few vol% of melt particles. Suevites occur outside the crater rim, carrying diaplectic crystals, coesite, and ballen quartz as well as true melt glasses and a variety of lithic clasts, among those spectacular staurolite-rich mica-schists. The recorded shock level in the uplifted target rocks is lower than expected and modeled. Shock recovery experiments with analogue carbonaceous graywackes at 34 and 39.5 GPa yielded nearly complete transformation of quartz into diaplectic glass. We therefore exclude a specific shock behavior of the soft, fluid-rich target material (carbonaceous graywackes, shales, slates) in core LB-08A as the prime or only reason for the melt deficit and the generally low shock levels recorded inside the Lake Bosumtwi impact crater.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.