Orogenic Tectonics

Structural, mineralogical and chemical studies show that the rocks from the Dabakala area, previously reported as gneisses and migmatites, are in fact syntectonic granitoid bodies. Three chemical associations are distinguished: (i) trondhjemitic (Dabakala tonalites and granodiorites), calc-alkaline (Finéssigué granodiorites and undifferentiated biotite granodiorites and granites) and peraluminous (Sarala hololeucocratic granites and Kowara muscovite trondhjemites). Most granitoids display deformation patterns typical of an interference between pluton emplacement and transpressional tectonics induced by a NNW-SSE to NW-SE compression which led to three major NS sinistral shear zones (N'Zi, Katidougou, Ouango-Fitini). Geochronological data (U-Pb ID-TIMS and SIMS zircon ages) yielded 2312 ± 17 Ma for the zircon cores from the Dabakala tonalite, 2154±1 Ma for the zircon rims of the same tonalite, 2162±32 Ma for Sarala, 2118±2 Ma for Kowara, and 2103±1Ma for Finéssigué. Sr-Nd isotopic data further indicate that all these rocks are isotopically primitive (0.7000 < 87 Sr/ 86 Sr < 0.7026, +1.8 <ε Nd(2.1Ga) + 3.7, 2039 <T DM < 2148 Ma, with the exception of the Dabakala tonalites: ε Nd(t) =-2.9, T DM = 2471 Ma). All the data suggest that these granitic rocks do not correspond to a reworked pre-Birimian crust as previously suggested. However, the genesis of the Dabakala tonalite involved recycling components of a 2.3 Ga pre-Birimian crust. A compilation of crustal residence ages for Birimian felsic sediments, volcanic and plutonic rocks at the scale of the whole Birimian crust in the Leo Rise could suggest that most of the Birimian felsic rocks arose, at least partly, from recycling of pre-Birimian differentiated crustal material. Therefore, it appears likely that the major Birimian s. s. (ca. 2170 Ma) and Bandamian (ca. 2105 Ma) growth events were preceded by an early Palaeoproterozoic crustal growth episode at ca. 2.3 Ga.

In Ghana the West African Craton is represented by Birimian and Tarkwaian rocks with extensive granitoid bodies. Granitoids from Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana were analysed for major and trace element contents and found to be characterised by highly-fractionated REE, enrichments, in LILE, and depletion in Nb, Ta and Sr. The LILE enrichment relative to strong Nb-Ta depression, indicates that these granitoids were emplaced in an active margin. Based on field relations, geochemical composition and geochronological data, the granitoids from the Kibi-Asamankese area can be divided into three types, namely; the Eburnean biotite granodiorite (2133-2127 Ma) and hornblende granodiorite (2147 Ma), and the Pre-Eburnean gneissic biotite granite (2193 Ma). The geochemical data of the studied rocks plot in the tholeiitic field, whereas on the A/CNK-A/NK diagram, they generally fall within the metaluminous field, with A/CNK values between 0.69 and 0.88. U-Pb dating of zircons in the granitoids yielded ages ranging from 2193 to 2127 Ma, which are among the oldest ages obtained from the granitoid plutons in Ghana. Such high-precision geochronological data indicate that magmatism occurred over a time-span of about 70 Ma. This provides further evidence that the period 2.1-2.2 Ga was one of the important stages of Birimian magmatism that led to the generation of the granitoids. From the above-mentioned ages, it is possible to link the geological activities to crustal processes and establish the cyclic geotectonic evolution in the West African Craton over time as part of an arc-back-arc basin system.

M D m , w ' premier Paleoproterozoic gold province (~10,000 metric ton gold endowment). Structural, metamorphic, and geochronological data suggest gold mineralisation occurred during three 2 episodes that span much of the Eoeburnean and Eburnean orogenic cycles. Eoeburnean orogenic and rare skarn-hosted gold deposits formed between ca. 2200 and 2135 Ma during repeated episodes of volcanism, plutonism, and shortening, which thickened the Paleoproterozoic crust. Early Eburnean orogenic and placer gold deposits formed between ca. 2110 and 2095 Ma during inversion, metamorphism, and subsequent oblique shortening of intra-orogenic basins filled after ca. 2135 Ma. This episode of mineral m w -M D m w m -Man Domain at ca. 2095 Ma. Late Eburnean orogenic and less common intrusion-related gold deposits formed between ca. 2095 and 2060 Ma during strike-slip to oblique-slip tecto , --m w w -M D m wm -Mossi Domain, whereas the Early Eburnean and Late Eburnean deposits include ca. 50-70% and 20-40%, respectively. Here, we highlight the favourable confluence of accretioncollision tectonics, involving juvenile crust formation as well as protracted magmatic, metamorphic, and deformation histories that resulted in di m -Mossi Domain.

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

M D m , w ' premier Paleoproterozoic gold province (~10,000 metric ton gold endowment). Structural, metamorphic, and geochronological data suggest gold mineralisation occurred during three 2 episodes that span much of the Eoeburnean and Eburnean orogenic cycles. Eoeburnean orogenic and rare skarn-hosted gold deposits formed between ca. 2200 and 2135 Ma during repeated episodes of volcanism, plutonism, and shortening, which thickened the Paleoproterozoic crust. Early Eburnean orogenic and placer gold deposits formed between ca. 2110 and 2095 Ma during inversion, metamorphism, and subsequent oblique shortening of intra-orogenic basins filled after ca. 2135 Ma. This episode of mineral m w -M D m w m -Man Domain at ca. 2095 Ma. Late Eburnean orogenic and less common intrusion-related gold deposits formed between ca. 2095 and 2060 Ma during strike-slip to oblique-slip tecto , --m w w -M D m wm -Mossi Domain, whereas the Early Eburnean and Late Eburnean deposits include ca. 50-70% and 20-40%, respectively. Here, we highlight the favourable confluence of accretioncollision tectonics, involving juvenile crust formation as well as protracted magmatic, metamorphic, and deformation histories that resulted in di m -Mossi Domain.

We present a thermal history of the Kedougou Kenieba Inlier (eastern Senegal), the westerncentral outcropping part of the West African Craton, based on 40 Ar/ 39 Ar analyses performed on hornblende, biotite, and K-feldspar minerals from Paleoproterozoic plutonic rocks. 40 Ar/ 39 Ar age spectra obtained for hornblendes and biotites range between 2055 ± 26 and 2028 ± 28 Ma, in very good consistency. They suggest that magmatism in the Kedougou Kenieba Inlier happened at the end of the Eburnean Orogeny (2.25-2.00 Ga). Taking into account previous zircon U/Pb ages, these new results imply that initial cooling from magmatic temperature to about 300°C (biotite closure temperature) occurred rapidly, and that these rocks did not experience any subsequent re-heating event above 300°C. On the other hand, 40 Ar/ 39 Ar age spectra obtained on K-feldspars display strongly disturbed patterns revealing that these minerals experienced argon loss due to re-heating events. Altogether, these data constrain a thermal history for the studied area involving two thermal events with temperatures around 275 and 225°C, at about 1750 and 1500 Ma, respectively. These thermal events, previously inferred from U/Pb ages of intruding mafic dykes, can be related to aborted attempts of continental breakup, as the West African Craton remained attached to Baltica and Amazonia cratons during the 1.8-1.3 Ga interval.

The Diale-Dalema metasedimentary series is exposed in the Kedougou-Kenieba Inlier that corresponds to the northwestern branch of the Eburnean orogenic belt in the southern West African Craton. Here we conducted a U–Pb geochronological study on metapelites, metagraywackes and metavolcanic breccia of the Diale-Dalema metasedimentary series in order to identify the sedimentary sources and establish the lithostratigraphic sequence of the Kedougou-Kenieba Inlier. This new U–Pb geochronological dataset from five samples representing different stratigraphic levels yield a dominant population of Paleoproterozoic detrital zircon grains with ages ranging from c. 2200 to 2100 Ma. The youngest weighted mean ages at c. 2120 Ma are identical for all five samples within error and provide a maximum deposition age for the sediments of the Diale-Dalema series. The dominant ages are similar to those obtained on metamorphosed plutonic and volcanic rocks of the Mako belt and thus suggest a dominant prox...

We present a thermal history of the Kedougou Kenieba Inlier (eastern Senegal), the western-central outcropping part of the West African Craton, based on 40Ar/39Ar analyses performed on hornblende, biotite, and K-feldspar minerals from Paleoproterozoic plutonic rocks. 40Ar/39Ar age spectra obtained for hornblendes and biotites range between 2055 ± 26 and 2028 ± 28 Ma, in very good consistency. They suggest that magmatism in the Kedougou Kenieba Inlier happened at the end of the Eburnean Orogeny (2.25–2.00 Ga). Taking into account previous zircon U–Pb ages, these new results imply that initial cooling from magmatic temperature to about 300 °C (biotite closure temperature) occurred rapidly, and that these rocks did not experience any subsequent re-heating event above 300 °C. On the other hand, 40Ar/39Ar age spectra obtained on K-feldspars display strongly disturbed patterns revealing that these minerals experienced argon loss due to re-heating events. Altogether, these data constrain a...

Paleoproterozoic basement in West Africa were distinguished via the interpretation of regional and high resolution magnetic airborne data of West African Craton (Jessell et al. 2015). Some of the dykes reach over 300 km in length and they are considered to be parts of much larger systems of mafic dyke swarms which are part of the plumbing system for Large Igneous Provinces (LIPs) and may be therefore used for the reconstruction of Precambrian supercontinents (e.g. Ernst, 2014). Five different dyke swarms in Burkina Faso, Niger, Ghana and Senegal were analysed and dated. From a petrographic and composition point of view, the mafic dykes correspond to tholeiitic basalts and are typically composed of plagioclase + clinopyroxene (augite) ± orthopyroxene (enstatite) ± olivine, and display a doleritic texture of variable grain size. Eleven ID-TIMS U-Pb ages obtained on baddeleyite (for details on the technique see Söderlund and Johansson, 2002) define five generations of Proterozoic age. ...