Title

L. P. Nikitina, N. M. Korolev, S. G. Scublov, V. N. Zinchenko, Joao Fransishku

Geochemistry and age eclogites xenoliths of diamondiferous kimberlite pipes Katoka and Kat-115 (Kraton Kasai, West Africa).

The first data on the chemical composition of eclogite xenoliths from the upper mantle beneath craton Kassai, West Africa and U-Pb (SHRIMP) age and geochemistry of zircons from that are represented. The types of eclogites, low- and high-MgO, high-Al2O3, their chemical composition (main, REE, HFSE) and crystallization conditions in a diamond phase are similar to eclogites in the mantle, underlying Man, Kaapvaal, Siberian cratons. Nb/Ta and Nb/La ratios in eclogites studied range from chondritic to superchondritic. This distinguishes the mantle eclogites from those of orogenic belts, characterizing by subchondritic and chondritic values. The zircon age values of low-MgO eclogites form discordia, the upper intersection with concordia is 1242 ± 97 Ma, and the lower – 194 ± 74 Ma. With account for the error the last value is close to the U-Pb age of zircons from kimberlites (117,9 ± 0,7 Ma) [34]. It is possibly, that disruption of U-Pb system in zircons is the result of kimberlitic magma disturbance. The oldest discordant value of age (2799 ± 9 Ma) obtained for zircons from high-Mg eclogite exceeds the age of the granite-gneiss found in Catoca kimberlites (2.6 billion; Sm-Nd method).
Key words: craton Cassai, upper mantle, eclogites, REE, HFSE, Nb/Ta, Nb/La ratios, zircon U-Pb (SHRIMP) age, zircon geochemistry.