Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast

A new synthesis of the geology and geochronology of the little-known Archaean rocks in Sierra Leone, Liberia, Guinea and Ivory Coast is presented in order to better understand the processes of Archaean crustal evolution in this region, and to attempt to interpret these data in the light of our current understanding of Archaean crustal evolution. In addition, this study seeks to identify those aspects of Archaean crustal evolution which are currently not known in this area and which need to become the subject of future studies, given the economic importance of this region in terms of the mineral deposits hosted in the Archaean rocks. These include greenstone-belt hosted iron ore, lode gold, chromite and columbite-tantalite and younger diamondiferous kimberlites intrusive into Archaean felsic gneisses. The new results show that this cratonic nucleus comprises of four main geological units: 1. The oldest crust is made up of 3.5-3.6 Ga TTG (tonalite-trondjemite-granodiorite) gneisses. These only outcrop in the east of the craton in Guinea but their presence is indicated elsewhere in the central part of the craton though xenocrystic zircon cores in younger rocks. 2. The major rock type found throughout the craton is 3.26-2.85 Ga TTG gneiss. In detail these magmas are thought to have formed in two episodes one between 3.05-3.26 Ga and the other between 2.85-2.96 Ga. The presence of inherited zircons in the younger suite indicate that this event represents the partial reworking of the older gneisses. 3.4 Ga eclogite xenoliths in kimberlite derived from the sub-continental lithospheric mantle are thought to be the restite after the partial melting of a basaltic protolith in the production of the TTG magmas. 3. Supracrustal rocks form linear belts infolded into the TTG gneisses and metamorphosed to amphibolite and granulite grade. They are of different sizes, contain a variety of lithological sequences and may be of several different ages. The larger supracrustal belts in Sierra Leone contain a thick basalt-komatiite sequence derived by the partial melting of two different mantle sources, unconformably overlain by a sedimentary formation. They are seen as an important resource for gold, iron-ore, chromite and columbite-tantalite. 4. A suite of late Archaean granitoids formed by the partial melting of the TTG gneisses in a craton wide deformation-metamorphic-partial melting event at 2800 +/- 20 Ma. This thermal event is thought to be responsible for the stabilisation of the craton. This new synthesis highlights major geological and geochronological similarities between the Archaean rocks of Sierra Leone, Liberia, Guinea and Ivory Coast and those in the Reguibat Shield in the northern part of the West African Craton suggesting that the two regions were once more closely related.UoD URS

Anti-CHIKV IgG/IgM and anti-MAYV IgG in Panel Samples According to Sociodemographic Characteristics.

Anti-CHIKV IgG/IgM and anti-MAYV IgG in Panel Samples According to Sociodemographic Characteristics.</p

Anti-CHIKV IgG by ELISA Seroprevalence in the Population Study between 2015 and 2019 According to Age and Sex.

Anti-CHIKV IgG by ELISA Seroprevalence in the Population Study between 2015 and 2019 According to Age and Sex.</p

Chikungunya-confirmed cases in São José do Rio Preto (SJRP), SP, between 2015 and 2019, according with epidemiological bulletins.

Chikungunya-confirmed cases in São José do Rio Preto (SJRP), SP, between 2015 and 2019, according with epidemiological bulletins.</p

Spatial distribution of <i>A</i>. <i>albopictus</i> mosquitoes positive for CHIKV according to qRT–PCR in Vila Toninho, <i>SJdRP-SP</i>.

Spatial distribution of Ae. aegypti and Ae. albopictus mosquitoes positive for CHIKV as detected by qRT–PCR (Ae. aegypti female and Aedes albopictus (purple), Ae. aegypti male (blue), Ae. aegypti female (yellow) and Ae. albopictus female (pink)) in this study, Vila Toninho, SJdRP-SP. Shapefile downloaded from https://portaldemapas.ibge.gov.br/portal.php#homepage.</p

Sociodemographic variables of the population study between 2015 and 2019.

Sociodemographic variables of the population study between 2015 and 2019.</p

Spatial Distribution of Samples from Population Study According to Anti-CHIKV IgG and PRNT Assays.

Thematic map showing the spatial distribution of positive (orange) and borderline positive (dark blue) serological results, according to anti-CHIKV IgG ELISA (A), and positive (red) or negative (blue) seroconversion samples from the population study, according to PRNT assays (B). Shapefile downloaded from https://portaldemapas.ibge.gov.br/portal.php#homepage.</p

Maximum likelihood tree of chikungunya virus based on partial envelope gene sequence.

Phylogenetic tree reconstructed using the Maximum-likelihood method with TIM2e+4 as nucleotide substitution model, using Ultrafast Bootstrap (UFBoot) combined with SH-like Approximate Likelihood-ratio test (SH-aLRT). The analysis involved 172 nucleotide (nt) sequences (1,885 nt). Branch lengths are drawn to a scale of nucleotide substitutions per site according to the scale. The analysis was conducted in IQ-TREE v. 2.0.3, and the final tree was visualized and edited in iTOL v. 6.6. The sequence from this study (1362|Brazil|2020) is highlighted in purple within the East/Central/South African genotype clade.</p

Fig 5 -

Spatial Distribution of Samples According to Serological Status for CHIKV (A) and MAYV (B) by PRNT assay in 2019 during the dengue outbreak in São José do Rio Preto, SP. Seroconversion results of patient samples in 2019 during the dengue outbreak in São José do Rio Preto, SP, illustrating the spatial distribution of serologic status by PRNT90 assay, which was positive (red) and negative (blue) for CHIKV (A) and MAYV (B) and positive (purple) for CHIKV/MAYV cross-reaction and positive (green) for MAYV (C). Shapefile downloaded from https://www.riopreto.sp.gov.br/mapas-rio-preto/.</p

The over dilution samples from dengue-suspected patients in the 2019 outbreak, which supported CHIKV and MAYV cross-reaction during neutralizing antibody titration (PRNT₈₀).

The over dilution samples from dengue-suspected patients in the 2019 outbreak, which supported CHIKV and MAYV cross-reaction during neutralizing antibody titration (PRNT80).</p