Geochemistry and Petrology of post-Archean dolerite intrusions in the Elogo Complex in the Ivindo Basement northwest of the Congo Craton

Geochemical and tectono-metamorphic study of post-Archean dolerite intrusions is carried out to reconstruct the petrogenesis and geodynamics of post-Archean intrusive mag- matism in the Congo Craton. Dolerites and hornblendites of the Elogo complex are characterized by a low-pressure greenschist metamorphism controlled by brittle micro tectonics and are metaluminous (A/NK: 4.47 and 7.84; A/CNK: 1.02 and 1.37) with a dominant tholeiitic affinity and affected by hydrothermal alteration (LOI = 1.13 – 8.7 %). LREE and Th enrichment, negative Nb and Ti anomaly, low Nb/Th, (Nb/La)PM < 1, Ti/Yb, Ce/La < 0.85, Nb/La < 1, and Ta/Th < 1 ratios, and high (La/Yb)n > 1 and (La/Sm)n > 1 define the dolerites geochemical signature as crustal contaminated. Al2O3/TiO2 (12.17 to 19.65), CaO/Al2O3 (0.60 to 0.78), (Gb/Yb)PM > 1 ( 1.15 to 1.32), and (Tb/Yb)n (1.13 to 1.29) ratios associated with the lack of HREE fractionation (Yb = 11.24 to 18. 01 ppm) characterize a shallow (1073.03 to 1189.92°c) spinel lherzolite-type mantle source with low melt rate (f = 10 to 20%), outside the garnet stability field [(Th/Ta)n < 1]. The negative Nb, Ti, Zr, Rb, and Ba anomalies, positive Hf, Th, and U anomalies, the moderate Cs and LREE (La and Ce) enrichment, and the REE fractionation [(La/Yb) n >1], associated with the high Ta contents, define an extensive intracratonic rift-type setting. The vein rocks originate from an asthe- nospheric uplift marked by lithospheric thinning in a Mezo-Neoproterozoic rift system that dislocated the Congo Craton inducing the genesis of the tholeiitic dolerites (1167 Ma and 850 Ma) of Nola in RCA and Yokadouma in Cameroon.