The 3000 km mantle transect through Angola and Congo based on diamond satellite minerals from kimberlites

The 3000 km SSW-NNE mantle transect through all Congo craton (including Angola and Congo DR) was constructed based on EPMA analyses of diamond satellite minerals (DSM) from  kimberlites (and placers) using monomineral thermobarometry (Ashchepkov et al., 2017)  and Surpher 8 software. It crosses Lucapa corridor from Kunene to Lushinga fields and goes from Mbuji-Mai and to Banalia field in Congo DR.  The NWW –SEE transect from Bas Congo to Kundelungu was built also.

The whole SW-NE profile consists of at least of 6 sections Angola part and 3 more in Congo DR part correspondently to the grouping of the kimberlites fields at the ancient mantle sub terranes. There are also heated regions with the higher concentrations of pipes correspondent to the boundaries of the sub terranes where the mantle columns are more heated and homogenized.

     Mantle sections show rather contrast layering. It is more evident and thin in P-FO2 diagram and total Fe# and less  for ToC and garnets CaO and Fe#.

      The section in Angola include several regions with the more dense  kimberlite population including Kunene, Cubango, Lubango and long array from Longo to Kamatue including Catoca cluster. The last highly diamondiferous part of mantle differ from other parts by the essential heating of the lower part of section relatively high amount of pyroxenitic and eclogitic material which probably define the high diamond grade. Several mantle clusters show heating and increase in Fe# accompanied by the low oxygen fugacity which corresponds to the high diamond grade In Angola: Cuilo – Liuele- Catoca and Camafuca Kamachia fields and in Congo DR – Mbuji- Mai and Wamba fields.

The relative homogenization beneath Catoca and close regions means more permeable mantle with concentration of proto-kimberlite magma chambers not only near the base of the lithospheric mantle, and also in intermediate and middle pyroxenite levels. The mineralogy suggests presence there and low-oxidized eclogites, dunites, and Mg-rich ilmenite-chromite-bearing metasomatites. Probably on such conditions many diamonds were growing during protokimberlite process in the large magmatic chambers near the lithosphere base where  large CLIPPIR type grains as megacrysts were growing.

The uppermost Early Archaean relatively thin plate mantle layers are inclined toward the  Catoca- Kamachia cluster in NNE  part of Congo where the concentration of eclogites are higher probably due subduction accretion.   RNF Grant 24-27-00411.

 

• Ashchepkov I.V., Zinchenko V.N., Ivanov A.S. Mantle Transects in Africa According to Data of Mantle Xenocrysts and Diamond Inclusions. In: Acta Geologica Sinica‐English Edition. Vol. 95(S1), pp.15-17 (2021).
• Zinchenko V., Ashchepkov I., Ivanov, A. Modelling of the mantle structure beneath the NE part of the Lucapa kimberlite corridor. Angola. In: Journal of science. Lyon, Vol.19. pp. 7-14. (2021).
• Ashchepkov I.V.; Ntaflos T., Logvinova, A.M., Spetsius, Z.V., Downes, H., Vladykin, N.V. Monomineral universal clinopyroxene and garnet barometers for peridotitic, eclogitic and basaltic systems. Geoscience Frontiers. Vol.8, pp.775-795. (2017).
• Ashchepkov I.V., Rotman A.Y., Somov S.V.et al. Composition and thermal structure of the lithospheric mantle beneath kimberlite pipes from the Catoca cluster, Angola. In: Tectonophysics. Vol. 530, pp.128-151 (2012).

RNF grant 24-27-00411.