Zadinian Gr

The West Congo Belt (WCB) is exposed, on 1,300 km, along the western margin of the CS. The West Congo Supergroup is divided into, from oldest to youngest, the rift-related volcanoclastic 999 ±7 Ma Zadinian and volcano-sedimentary ±910 Ma Mayumbian groups deposited on a ±2.1 Ga polymetamorphic Kimezian basement, and the overlying sedimentary West Congolian Group.

Synonym:

References: Deblond and Tack, 2001; Tack et al., 2001.

[Fig 1. Simplified geological map of the Congo Basin, compiled from various published map. The stratigraphic units have been assembled into major sequences (Late Neoproterozoic, Paleozoic and Cenozoic)]

[Fig 2. Tectonic setting of the Neoproterozoic basins of present-day Central Africa, compiled from the 1: 2M geological map of the Zaire (Lepersonne, 1974a) and the 1:4M map Geology and Major Ore Deposits of Africa (Milesi et al., 2006)]

[Fig 3. Lithostratigraphic synthesis for the Neoproterozoic to Early Paleozoic period. Compiled after various authors. Dotted lines between Banalia, Alolo and Galamboge formations: stratigraphic transition by recurrences]

[Fig 4. Lithostratigraphic columns for the Congo Basin established using data from the 4 wells in the central part of the basin and outcrops on its NE margin (Lindi-Ubangi and Kisangani-Kindu region), compared with the West-Congo and Katanga stratigraphy]

[Fig 5. Simplified geological map of Sub-Saharan Africa showing the Neoproterozoic basins on and around the Congo Shield (modified after De Waele et al. 2008). (LC) Lower Congo Basin, (Co) Comba Basin, (Sa) Sangha Basin, (Ny) Nyanga-Niari Basin, (An) Angola Basin, (SO) Semb-Ouesso Basin, (Ba) Ubangui Basin, (LiB) Likki-Bembe´ Basin, (Bk) Bakouma Basin, (Fou) Fouroumbala Basin, (Li) Lindi Basin, (It) Itombwe Basin, (Ma) Malagarazi-Bukoban Basin, (Mb) Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin, (Lu) Luamba Group, (Kat) Katanga Basin, (RB) Ruwenzorian Belt, KaB) Karagwe-Ankole Belt, (RuB) Ruzisian Belt, (KiB) Kibaran Belt, (UB) Ubendian Belt, IB Irumide Belt]

[Fig. 6. Western margin of the Congo Shield. (A) Sketched geological map of the West Congo Belt (modified after Frimmel et al. 2006)]

[Fig. 7. Synthetic stratigraphic log combined with C and Sr isotopic curves of the West Congolian Group in the DRC (modified after Tait et al. 2011). Note strontium isotope ratios of the Haut-Shiloango Subgroup ranging between 0.7068–0.7072 (Frimmel et al. 2006; Poidevin 2007) and of the C3 to C5 formations of the Schisto-Calcaire Subgroup ranging between 0.7074 to 0.7084 suggesting deposition, respectively, between 800 Ma and 650 Ma and between 635 and 575 Ma (Frimmel et al. 2006; Poidevin 2007; Delpomdor and Pre´at 2013) and the negative shift of -13 ‰, consistent, in absolute values, with the negative swing of the Trezona anomaly (Halverson et al. 2007)]

[Fig. 8. Stratigraphic correlation between the Neoproterozoic sedimentary basins in Central Africa. Correlations based on Sr isotopic data, radiometric age constraints and revised lithological relationships]

"The lower part of the Zadinian Group (Tack, 1975a,b; Cahen et al., 1984) is composed of basal, continental, siliciclastic metasediments (including black shales), not exceeding 1500 m in thickness, that exhibit strong lateral and vertical facies variations, consistent with a continental rift environment. In DRC, these sedimentary rocks are overlain by a 1600 to 2400 m thick sequence of mafic rocks (Large Igneous Province?), described under various local names (Gangila metabasalts in type area; Tack, 1975a,b; 1979b,c). … Both to the north and to the south of the DRC, the basaltic activity is strongly reduced. In the Congo-Brazzaville, amphibolitic lenses … interbedded in the “Bikossi” metaquartzites are considered as limited lateral equivalents of the Gangila basalts." [Deblond and Tack, 2001]

ca. 999 +/-7 Ma at base, overlain by Mayumbian Gr lavas with 920 +/-8 Ma at their base (Tack et al., 2001) => rounded here as 1000 to 916 Ma (lower 30% of Tonian)

Both the Zadinian Gr and Mayumbian Gr represent early Neoproterozoic magmatic events marking the initial continental rifting of the Rodinia supercontinent before its breakup (Tack et al., 2001). " Emplacement of early Zadinian peralkaline granites (Noqui massif, 999 +/-7 Ma) and rhyolites (Palabala) was accompanied by incipient rift sedimentation, corresponding to the onset of trans-tensional rifting, preferentially in a transverse mega-shear setting along the margin of the Congo craton. Subsequent upper Zadinian magmatism produced a thick (1600–2400 m) basaltic sequence (Gangila basalts), which has geochemical characteristics typical of continental flood basalts. The Gangila basalts, associated with major pull-apart rifting, were followed rapidly by the 3000–4000 m thick Mayumbian Gr rhyolitic lavas, dated at 920 +/-8 Ma at the base and 912 +/-7 Ma at the top." (Tack et al., 2001)