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Minerals 2018, 8(2), 73; https://doi.org/10.3390/min8020073

Role of Volcano-Sedimentary Basins in the Formation of Greenstone-Granitoid Belts in the West African Craton: A Numerical Model

1
School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
2
Geosciences Environnement Toulouse, Observatoire Midi Pyrénées, 31400 Toulouse, France
3
Department of Earth Science, University of Ghana, P.O. Box LG 25, Legon, Accra, Ghana
*
Author to whom correspondence should be addressed.
Received: 20 December 2017 / Revised: 11 February 2018 / Accepted: 12 February 2018 / Published: 17 February 2018
(This article belongs to the Special Issue Geological Modelling)
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Abstract

Greenstone belts in the West African Craton (WAC) are separated by several generations of granitoids intruded at ca. 2.18–1.98 Ga. Simultaneous folding and exhumation play an important role in the formation of greenstone-granitoid belts. However, the overall tectonic regime and origin of granitoids remain controversial. In this study, we present the estimates of the mantle potential temperature (Tp) for the WAC, which yields values of about 1500–1600 °C, pressure estimates of initial and final melting yield values of about 3.7–5.2 GPa and 1–1.3 GPa, respectively. Subsequently, 2D thermo-mechanical models have been constructed to explore the width of volcano-sedimentary basin on spatial-temporal evolution of diapirs that emplaced in the lower-middle crust during compression. The models show that the width of the volcano-sediment layer plays an important role in the formation mechanisms of greenstone-granitoid belts. The lower crust beneath sedimentary sequences is deformed into a buckle fold during the first compressional stage, through which relief uplifts slowly. Subsequently, the buckle fold is further deformed into several individual folds. Diapirs made of lower crust rocks ascend and emplace in the middle-upper crust resulting from instability. Benefitting from the mantle temperature, the pressure estimates and the numerical modelling results, a new geodynamic model was constructed. This model indicates that a series of sheet-like granitoids possibly derived from either subducted mélanges, lower crust and/or mantle melting that are accumulated at depths of the subcontinental mantle would channel along diapirs before feeding the upper crust. When the granitoids arrive at the solidified lids of the diapirs, they would favour migrating horizontally and intrude into the upper crust through weakening zones between the diapirs. Our geodynamic model also suggests an asymmetry of structures between the upper and middle-lower crust, with the dome-like granitoids overlying high-grade sedimentary synforms and high-grade diapirs underlying low-grade greenstone belts. View Full-Text
Keywords: mantle potential temperature; olivine liquidus temperature; thermo-mechanical model; exhumation; Eburnean Orogeny; West African Craton (WAC) mantle potential temperature; olivine liquidus temperature; thermo-mechanical model; exhumation; Eburnean Orogeny; West African Craton (WAC)
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Feng, X.; Wang, E.; Ganne, J.; Amponsah, P.; Martin, R. Role of Volcano-Sedimentary Basins in the Formation of Greenstone-Granitoid Belts in the West African Craton: A Numerical Model. Minerals 2018, 8, 73.

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