EBURNEAN OROGENY PDF
The Eburnean orogeny in Africa results from the continental collision between the San Francisco and Congolian cratons. The different stages of this orogeny in. We have investigated three greenstone belts (Boromo, Houndé, and Banfora) and associated granitoid terrains, which form part of the Eburnean orogen. These metamorphic and structural characteristics provide new constraints for the geodynamical evolution of the Eburnean orogeny in the North.
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It occurred whilst I was sweating away in a cocoa plantation on the hunt for outcrop, in the hope of furthering our understanding how the Earth was changing around two billion years ago, during its teenage years.
My research focuses on the geology of central SW Ghana, with the aim of furthering the understanding of crustal evolution and accretion of the West African Craton during the Palaeoproterozoic.
The Palaeoproterozoic domain is unique in that it is dominated by vast, alternating granite-greenstone provinces bound by craton-scale shear zones, reminiscent of Archean domains. The craton, therefore, provides us with an opportunity to study how Earth processes evolved at the Archean-Palaeoproterozoic boundary, relative to eburbean well-constrained processes occurring today.
Furthermore, it represents the first orogenic event during a period of global orogenesis between 2. In total, I spent four and a half months in the field, split over two field seasons during the early months of and GSD provided the bulk of our logistical support, much eburneqn which had been previously arranged by Kwame Boamah, Head of Geophysics.
Before reconnainsance of my field area could begin, we had a meeting scheduled with another of my aceadmeic supervisors, Lenka Baratoux, and Sylvain Block, in Orobeny, km to the northwest.
The roads were bumpy and laden with traffic of all shapes and sizes, meaning the trip took us the better part of two days. During our first week, we explored the high grade terranes and vast granite provinces of NW Ghana, followed by a visit to the Bui Greenstone Belt in central west Ghana.
For me, the real work started when we arrived at my field area, covering irogeny Sefwi Greenstone Belt and the adjacent Sunyani and Kumasi metasedimentary provinces.
Here we confronted the biggest challenge of mapping in southwest Ghana: The field area spans about 60 km 2and is largely covered by cocoa plantations, impenetrable forest reserves, and thick regolith cover, grading into drier, sparser vegetation in the far north of the field area. All of these features pose challenges when designing a field campaign.
We utilised existing geological maps, old outcrop databases and regional geophysical datasets, including aeromagnetic and radiometric surveys, to target key localities for gathering lithological, petrophysical, metamorphic and structural data and collecting representative samples.
Like eburrnean a needle in a haystack! An outcrop of tonalite exposed in an dry stream in the Ayum Forest Reserve. The majority of my field work was spent in the company of my driver, Kwasi Duah, to whom I am heavily indebted.
We utilised local knowledge, asking farmers if they knew of any nearby exposures.
Kwasi bottom right and a group of farmers who lead us to an outcrop west of Kenyase. Field kit included the standard hammer, compass, hand lens, GPS and machete. Some of the more unique challenges encountered during field work in Ghana led to a new appreciation for particular pieces of field equipment that I had rarely used before. I saw the true purpose of the waterproof pages in my notebook as the sweat streamed off my face in the heat and high humidity.
And I was strangely comforted to be surrounded by people carrying machetes when we came across the wide, muddy trail of a python whilst hunting for outcrop in dense forest. Other exceptional experiences included sitting down with village chiefs to explain the purpose of our research and request permission for access to nearby outcrop.
Unfortunately for geologists, this also means increased weathering of rocks exposed at the surface. Our diet staples were fresh bread, sardines, avocado, and tomato, plus pawpaw, coconut and orange depending on what was being sold in the stalls we passed.
For dinner, we feasted either on fufu mashed cassava and plantain or banku corn and cassava doughwhich you break off and roll into a ball with your right hand and dip in a hot groundnut or light soup. We also ate quite a lot of goat, dried fish, and chicken, and I was once honoured with the head of a bush rat, which, I can assure you has a particularly strong smell and flavour.
Bush meat caught by farmers ebutnean accompanied us through one of the forest reserves near Nkwanta. The two field campaigns proved to be highly successful, with close to outcrops documented, greatly bolstered by additional outcrop databases supplied by Newmont and Kinross. Eburndan gathered were used for microstructural constraints and metamorphic P — T modelling, as well as new geochemical and geochronological data to constrain the geodynamic setting and timing of magmatism, sedimentation, metamorphism and deformation.
The crew perched atop the megacrystic leucogranitic Eburndan Mountains. The greenstone belt threw up a few surprises, including outcrops of migmatitic garnet-kyanite-biotite paragneisses and amphibolites.
From these samples, metamorphic modelling revealed previously undocumented high-pressure assemblages, with P-T-t-D paths indicating collisional orogenesis, high grade metamorphic and subsequent lower crustal exhumation occurred in the study area around 2. This combined with the limited number of regional studies in the Sefwi Greenstone Belt opened up a fascinating and untapped research avenue into Palaeoproterozoic geodynamics.
All of the geologists who have previously worked on the Sefwi belt and the surrounding areas must have faced similar challenges of outcrop sparsity, pervasive weathering, and thick ground cover.
But with perseverance, our field work provided a few little threads to help us unravel the history of the West African Craton. Geological map of Africa 1: Home Posts Map Gallery. Menu Skip to content. My meeting with the chief of Siana.
The Harmattan hanging over forest and banana plantations. Garnet bearing migmatitic paragneiss from Chiraa.