Geochemical and geochronological signatures of granitoids from the Chaillu massif, Congo Craton: Insights into Mesoarchean crustal growth - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Precambrian Research Year : 2024

Geochemical and geochronological signatures of granitoids from the Chaillu massif, Congo Craton: Insights into Mesoarchean crustal growth

Louis-Marie Djama
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Abstract

We present new geochemical and geochronological data for Mesoarchean to Neoarchean plutons of the Chaillu inlier of the Congo Craton that demonstrate an evolution of magma sources in relation with crustal growth. Four distinct plutonic suites were newly identified: (1) sodic low medium/high-pressure tonalite-trondhjemite-granodiorite, (2) Mg–K-rich monzogranite to monzodiorite (sanukitoids), (3) K-rich monzogranite–syenogranite, (4) K-rich granodiorite–monzogranite with medium/high-pressure TTG-like signatures. The TTGs are metaluminous to slightly peraluminous, silica-rich magmatic rocks (SiO2 > 67.5 wt%) with high contents of Na2O (3.5 < Na2O < 6.2 wt%), and low contents of ferromagnesian oxides, and K2O contents (K2O < 2.6 wt%). The sanukitoids (s.l.) are metaluminous to slightly peraluminous, with a large range of silica contents (53 < SiO2 < 69 wt%), high Mg# (42–74) and potassic with variable K2O contents (1.2 < K2O < 5.0 wt%). The high-K granites are slightly peraluminous, with high silica contents (SiO2 > 67.7 wt%), low amounts of ferromagnesian oxides, and a clear potassic signature, with K2O contents (2.5 < K2O < 4.7 wt%), and K2O/Na2O ratios higher than 0.55. The zircon U–Pb dating results indicate that: i) TTGs emplaced between 3012 ± 16 Ma and 2840 ± 9 Ma; ii) sanukitoids between 2853 ± 14 Ma and 2832 ± 9 Ma; and iii) are K-rich biotite granites between 2893 ± 11 Ma and 2847 ± 16 Ma. Two main well-defined periods are identified: i) one of TTG-type magmatism between 3.02 and 2.92 Ga; and ii) one of sanukitoid-TTG-biotite granite-type association between 2.91 and 2.82 Ga. Such temporal evolution from TTG-domination through coexisting sanukitoids (s.l.) – TTGs – biotite granites during the late-Archean in the Congo Craton resembles other Archean cratons, such as the Dharwar, North China, Karelian, Superior Province, Pilbara, Kaapvaal, São Francisco and Amazonian.
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insu-04591828 , version 1 (29-05-2024)

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Olivier Blein, Thomas Fullgraf, Maxime Padel, Jérémie Melleton, Matthieu Chevillard, et al.. Geochemical and geochronological signatures of granitoids from the Chaillu massif, Congo Craton: Insights into Mesoarchean crustal growth. Precambrian Research, 2024, 409, pp.107435. ⟨10.1016/j.precamres.2024.107435⟩. ⟨insu-04591828⟩
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