Early Proterozoic crustal evolution in the birimian of Ghana: constraints from geochronology and isotope geochemistry

doi:10.1016/0301-9268(92)90086-4

Precambrian Research

Volume 56, Issues 1–2, April 1992, Pages 97-111

https://doi.org/10.1016/0301-9268(92)90086-4 Get rights and content

Abstract

Representative suites of Ghanaian granitoids, metavolcanics and metasediments were selected from Birimian rock units for RbSr, Pb/Pb and SmNd analyses. Isotopic data on the igneous rocks provide evidence for a major Early Proterozoic crust-forming episode which took place over a maximum time interval from ∼ 2.3 to ∼ 2.0 Ga by a differention from a depleted mantle source. There is little evidence for the involvement of significantly older (e.g. Archaean) crust in the genesis of the igneous rock units. The only exception so far found is the Winneba granitoid, which appears to contain a magmatic contribution from presumably underlying Archaean basement. SmNd model ages indicates that Birimian sediments were derived from adjacent penecontemporaneous volcanic belts.

The Birimian of Ghana forms part of a major Proterozoic (Eburnean) episode of juvenile crustal accretion which has been recognised in the surrounding areas of Mauretania, Senegal, Ivory Coast, Burkina Faso, Mali and Niger, where it has been dated at 2.1–2.2 ga (abouchami et al.) The Birimian terranes bridge a major gap in mantle activity and associated crustal evolution for a period considered as quiescent on other continents.

References (22)

B. Bessoles
Le Craton Ouest-Africain
S.L. Goldstein et al.
A SmNd isotopes study of atmospheric dusts and particulates from major river systems
Earth Planet. Sci. Lett.
(1984)
G. Gruau et al.
RbPb and SmNd geochronology in Lower Proterozoic granite-greenstone terrains in French Guiana, South America
Precambrian Res.
(1985)
P. Kolbe et al.
RbSr study on country rocks of the Bosumtwi Crater, Ghana
Geochim. Cosmochim. Acta
(1967)
A. Leube et al.
The Early Proterozoic Birimian Supergroup of Ghana and some aspects of its associated gold mineralisation
Precambrian Res.
(1990)
R.G. Miller et al.
Crustal residence ages of clastic sediments, orogeny and continental evolution
Chem. Geol.
(1986)
R.J. Pankhurst et al.
Determination of Rb/Sr and ⁸⁷Sr/⁸⁶Sr of some standard rocks and evaluation of X-ray fluorescence spectrometry in RbSr geochemistry
Chem. Geol.
(1973)
P. Richard et al.
¹⁴³Nd/ ¹⁴⁴Nd, a natural tracer: an application to oceanic basalts
Earth Planet. Sci. Lett.
(1976)
W. Abouchami et al.
A major 2.1 Ga event of mafic magmatism in West Africa: an early stage of crustal accretion
J. Geophys. Res.
(1990)
M. Caen-Vachette
Récapitulation des âges radiométriques déterminés sur les formations cristallines et cristallophylliennes de l'Afrique de l'Ouest

D.J. DePaolo

Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Proterozoic

Nature

(1981)

Cited by (203)

A combination of multivariate statistics and machine learning techniques in groundwater characterization and quality forecasting
2024, Geosystems and Geoenvironment
Globally, the quality of groundwater has proven to have been affected by some natural and human activities in recent years. To ensure there is good drinking water (Sustainable Development Goal 6.3, there is a need to elucidate the groundwater quality status of the area of interest. The groundwater in the northwestern parts of Ghana is not yet well characterized. Hence, this study employed a multi-method approach of hydrochemistry, water quality index (WQI), multivariate statistics, and machine models: multiple linear regression (MLR), decision tree regression (DTR), random forest regression (RFR), and artificial neural network (ANN), are combined in the characterization and prediction of the water quality in the area. They are robust in providing conclusions on groundwater assessment that can be relied upon for decision-making processes regarding groundwater usage and monitoring. Except for NO₃⁻ and TDS exceeding their standard levels in 22 and 2 locations, respectively, the other physicochemical parameters are within acceptable limits. The groundwater is generally good for domestic usage based on the WQI, with 79.2% of excellent to good waters. The groundwater evolved from Na-type, Cl-type, and Cl(SO₄)-Ca(Mg) facies. Agricultural activities are the main source of human impact on the groundwater. Silicate mineral dissolution and ion exchange processes are the natural processes that affect groundwater mineralization, with mineral dissolution being the dominant process. Based on the performance metrics: MAE, MSE and RMSE of the ML methods considered in the WQI forecasting, the order of performance of the models is ANN > RFR > DTR > MLR, with the following respective R² values 0.9974, 0.9193, 0.8966 and 0.8886.
Rheological context of emplacement of the Dori, Gorom-Gorom and Touka Bayèl granitic plutons (northeast Burkina Faso, West African Craton)
2023, Journal of African Earth Sciences
The reconstitution of the geodynamic processes of the Eburnean orogeny in the time span around 2.1 Ga in Dori area is here carried out through the examination of the internal structures and microstructures of the Dori, Gorom-Gorom and Touka Bayèl granitic plutons. The radiometric ages of these plutons vary between 2164 Ma and 2148 Ma. The internal structures have been evidenced using the Anisotropy of Magnetic Susceptibility (AMS) method and the examination of microstructures through thin sections under optical microscope.
The organization of the internal fabrics strongly suggests a diapiric emplacement for the Dori and the Touka Bayèl plutons in a still soften crust. The pluton of Gorom-Gorom seems to be constituted of four small plutons. Three of them, coalescent in the southern part, are emplaced by the diapirism and the fourth in the northern part can be interpreted as emplaced in a tension gash.
The overall disposition of the fabrics lets suggest a synchronous emplacement in accordance with the dextral sense of the Tiébélé-Dori-Markoye (TDM) shear zone in a regional E-W shortening context responsible of a crustal thickening.
The two emplacement mechanisms (diapirism and tension gash) identified through the internal fabrics testify a rheological contrast of the crust during this early period of the Eburnean Orogeny.
Magmatic arc construction within the Kedougou-Kenieba inlier, eastern Senegal: Petrographic, lithogeochemical and radiogenic isotope constraints
2023, Journal of African Earth Sciences
New petrographic, lithogeochemical and radiogenic isotope results from magmatic intrusions of the southeastern part of the Kedougou-Kenieba Inlier, Senegal document that these intrusions display evidence of a magmatic continuum of medium to high-K composition. A low-K intrusion group consists of andesitic, dioritic and tonalitic compostitions, with moderate (La/Yb)_N and low (Dy/Yb)_N ratios ranging, respectively, from 7.3 to 21.4 (with an average of 17.3) and 1.0 to 1.5. These intrusions have no obvious Eu anomalies (Eu/Eu* = 0.90–1.17), an average SiO₂ concentration of 60.5 wt%, and are enriched in MgO, with an average concentration of 4.1 wt%. Their ε_Nd values are high and range from +5.16 to +8.88, whereas they have low ⁸⁷Sr/⁸⁶Sr_i ratios of 0.701380–0.702552. This geochemical signature is characteristic of a depleted mantle source, which is supported by high Ni concentrations up to 211 ppm and high Mg# up to 85.35. The high-K leucogranite is characterized by high (La/Yb)_N and higher (Dy/Yb)_N ratios of, respectively, 10.6–48.3 (with an average of 30.5) and 2.0 to 2.4. It displays strong negative Eu anomalies (Eu/Eu* = 0.33–0.52), and has a higher average SiO₂ concentration of 74 wt%, lower MgO concentration with an average of 0.21 wt%, as well as lower ε_Nd values below −1.95. This geochemical signature suggests a continental crustal source for the magmas. Between these two end-members, there is an intermediate group of medium to high-K intrusions including quartz diorite, tonalite, granodiorite and monzogranite. These rocks are characterized by a wide variation of geochemical compositions and are most likely the result of a mixing of different magmatic sources and extreme fractional crystallization processes. Furthermore, we demonstrate that these magmatic intrusions were formed in a volcanic arc. These new data are evidence for a diversity of the intrusions within the southeastern part of the Kedougou-Kenieba Inlier.
Characterisation and rare-metal potential of the Winneba-Mankoadze pegmatites, Southern Ghana: Evidence of two pegmatite fields
2023, Journal of African Earth Sciences
In southern Ghana, the region along the coast between Accra and Cape Coast hosts a large number of pegmatites mineralized in lithium, niobium-tantalum and tin. The pegmatites occur in many distinct groups, each extending over several kilometers. They intrude metasedimentary units of the Birimian Supergroup, and are associated with early to late orogenic granite intrusions which are metaluminous, sterile, and too old to be potential parental granites for the pegmatites. In this study, we characterized the Winneba-Mankoadze group of geographically coeval pegmatites, using field description, petrography, rare-metal mineralogy and accessory mineral geochemistry on micas, garnet and Nb–Ta–Sn minerals, in order to determine its rare-metal potential and to investigate its origin. The results indicate that the pegmatites are part of the albite-spodumene type of the Lithium–Cesium–Tantalum (LCT) family. The rare metal mineral assemblages are particularly complex and display relevant oxide species such as columbite- and wodginite-group minerals, tapiolite, microlite, cassiterite and rutile, which are evidences of an extremely evolved magmatic system. Based on mineral assemblages, whole-rock geochemistry, and mineral geochemistry on garnet, micas and the CGM, two pegmatite fields are distinguished in the Winneba-Mankoadze group, and an anatectic origin is proposed. For the first time in West Africa, we fully describe a highly fractionated LCT-family pegmatite field comparable to the most evolved pegmatite bodies in the world.
Mapping subsurface geological structures in the Birimian Supergroup, Ghana using airborne magnetic and radiometric data: Implications for gold exploration
2023, Journal of African Earth Sciences
Rarity of outcrops is a typical feature of considerable parts of the Birimian Supergroup in Ghana as a result of deep weathering which leads to the formation of thick surficial cover and laterization. This hampers the precise mapping of lithological boundaries and mafic dykes. These boundaries are tectonic contacts that may have the potential to host orogenic gold deposits. This study aims to map these subsurface geological features using regional airborne geophysical data. Derivatives of magnetic data such as analytic signal, vertical derivative, horizontal gradient and the ternary map of the radiometric data were employed to interpret subsurface geology. The general correlation of the magnetic and radiometric maps with the existing geological map confirms their suitability as geological mapping tools. Tectonostratigraphic contacts of several geological domains within the Birimian Supergroup were delineated. These zones host world-class gold deposits and are potential corridors to focus exploration activities to ensure efficient fund utilisation and minimisation of exploration risks. Additionally, SSE-NNW, WSW-ENE and WNW-ESE trending dolerite dyke swarms were outlined.
Constraints on Paleoproterozoic crustal growth from Birimian Supergroup lavas of the Bui belt (Ghana) in the West African Craton
2023, Precambrian Research
The volcano-metasedimentary Bui belt in Ghana is one of the lesser known Birimian belts of the West African Craton that provide constraints on Paleoproterozoic crustal growth. This study presents the first major, trace element and Nd-Hf isotope data for the mafic suite of the Bui belt to constrain their petrogenesis and geodynamic setting. Although alteration is prevalent, the volcanic, volcaniclastic and plutonic rocks show tholeiitic signatures, with Mg# 35–65. Chondrite-normalised REE patterns are mainly flat, with slight LREE enrichment or depletion, and multi-element diagrams show Th and LREE depletion relative to other immobile incompatible trace elements. These features suggest derivation from a moderately depleted mantle source. Whole rock Sm-Nd isotope data yields an errorchron at ca. 2.2 Ga, with an initial εNd of +3.4 but the Lu-Hf isotopic system appears to be disturbed. The lack of arc related geochemical signatures (absence of negative Nb-Ta and Ti peaks, a nearly flat to depleted REE pattern) in the Bui mafic suite, together with the volcanic-sedimentary rock association, point towards magma generation in an oceanic plateau or divergent setting similar to a mid-ocean ridge, contrasting with the subduction setting that has been proposed for most other instances of Birimian magmatism in the West African Craton.

View all citing articles on Scopus

¹: Present address: Woodstock School, Mussoorie, U.P. 248179, India.

View full text

Research paperEarly Proterozoic crustal evolution in the birimian of Ghana: constraints from geochronology and isotope geochemistry

Abstract

Earth Planet. Sci. Lett.

Precambrian Res.

Geochim. Cosmochim. Acta

Precambrian Res.

Chem. Geol.

Chem. Geol.

Earth Planet. Sci. Lett.

A major 2.1 Ga event of mafic magmatism in West Africa: an early stage of crustal accretion

J. Geophys. Res.

Récapitulation des âges radiométriques déterminés sur les formations cristallines et cristallophylliennes de l'Afrique de l'Ouest

Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Proterozoic

Nature

Research paper
Early Proterozoic crustal evolution in the birimian of Ghana: constraints from geochronology and isotope geochemistry