Disclosed data from mantle xenoliths of Angolan kimberlites based on LA-IPC-MS analyses

ROBLES-CRUZ, S.E.; ESCAYOLA, M.; MELGAREJO, J.C.; WATANGUA, M.; GALÍ, S.; OLIMPIO, A.; JACKSON, S.

Budapest

Conferencia; Bonds and Bridges: Mineral Sciences and their Applications; 2010

The diamondiferous Catoca and Cucumbi-79 kimberlite pipes are located on the Kasai Craton, Angola. Different suites of mantle xenoliths have been characterized by optical petrographic and SEM-BSE studies. Three types of xenoliths are found in Catoca: eclogites, garnet clinopyroxenites (with G9 [1] garnets and chromian dipside), and garnet lherzolite (with G9 garnets and chromian diopside). Phlogopite is found as a rare accessory in Catoca peridotites. In contrast, the Cucumbi-79 kimberlite contains at least the following types of xenoliths: garnet clinopyroxenites (with G5 garnet, diopside and phlogopite), garnet lherzolites (showing different proportions of G5 or G9 garnets, chromian diopside, enstatite and phlogopite), PIC suite xenoliths (phlogopite, ilmenite, diopside) and glimmerites. Two main different trends for garnet can be identified in Catoca depending on the REE patterns. Eclogitic garnet has “normal” [2] REEN patterns, while garnet from lherzolite xenoliths usually has “sinusoidal” [2] REEN patterns and rarely “normal” REEN patterns. Eclogitic clinopyroxene is LREE-enriched. Garnet from the lherzolite xenoliths is characterized by a LREE-enrichment, a maximum around the LREE-HREE limit and flat HREE. Unlike in Cucumbi-79, garnet from lherzolite xenoliths presents “normal” patterns with lower REE values. Garnet from phlogopite-rich xenoliths presents “normal” patterns, but their values are significantly (about 10x chondritic value) lower. Only clinopyroxene from phlogopite-rich xenoliths exhibits higher values in LREE than the same xenoliths in Catoca. Data indicate that the mantle sampled by these two kimberlites might have been under different equilibration conditions and different degrees of metasomatism. Hence, the “normal” pattern exhibited by the Cucumbi-79 garnets might be explained as the result of refertilization of previously depleted peridotite by infiltration of melt [3]. In contrast with garnet patterns in Cucumbi-79, the “sinusoidal” REEN patterns of garnet from lherzolite xenoliths in Catoca may be the result of