The age and petrology of the Chimbadzi Hill Intrusion, NW Zimbabwe: first evidence for early Paleoproterozoic magmatism in Zimbabwe
✍ Scribed by Tawanda D. Manyeruke; Thomas G. Blenkinsop; Peter Buchholz; David Love; Thomas Oberthür; Ulrich K. Vetter; Donald W. Davis
- Book ID
- 104019860
- Publisher
- Elsevier Science
- Year
- 2004
- Tongue
- English
- Weight
- 827 KB
- Volume
- 40
- Category
- Article
- ISSN
- 1464-343X
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✦ Synopsis
The mafic-ultramafic Chimbadzi Hill intrusion in the NW of the Zimbabwe craton is a dyke with inward-dipping margins comprising magnetite peridotite, troctolite and magnetite melatroctolite. The magnetite peridotite is composed of about equal amounts of V-and Ti-bearing magnetite and olivine ($Fo 60 ). The troctolite is composed of about 50% olivine ($Fo 50-54 ), 40% plagioclase (An 53-58 ), 7% clinopyroxene and minor apatite and magnetite with ilmenite lamellae. Geochemical trends suggest that the Chimbadzi Hill Intrusion formed by fractional crystallisation from a single initial magma. However, the more primitive magnetite peridotite overlies the more evolved troctolite in the intrusion. This ÔapparentÕ inverted stratigraphy may be due to emptying of a fractionated magma chamber from the top, or to floor subsidence during intrusion.
U-Pb dating on baddeleyite reveals that the age of the Chimbadzi Hill Intrusion is 2262 ± 2 Ma. This age does not correspond to any known tectono-thermal event in the Zimbabwe Craton or adjacent metamorphic belts. It is $300 Ma younger than the late Archean Great Dyke, and $230 Ma older than other Paleoproterozoic events in and around the craton. Therefore, it may represent a so far undocumented very early Proterozoic igneous event in the Zimbabwe Craton. The intrusion represents a vanadium resource for Zimbabwe, with titanium potentially being mined as by-product.