An integrated geochemical and isotopic study of the Prieska Province kimberlites from the Republic of South Africa

[摘要] Rb-Sr emplacement ages of nineteen kimberlites from the Prieska Provincevary from 74 to 174 Ma, Their isotopic, whole-rock geochemical signaturesand perovskite REE distributions were also determined.Non-micaceous and micaceous kimberlites from the area show similarpetrographic, geochemical and isotopic compositions relative to cratonickimberlites, indicating similar sub-continental mantle source compositionsin the two tectonic environments. Transitional varieties of kimberlite,which can be defined petrographically, geochemically and isotopically arealso recognised from the area, but are not prevalent in the cratonicenvironment. The Prieska Province kimberlites are possibly derived bypartial melting processes within a subcontinental reservoir characterised bya spectrum of compositions from time-averaged depleted (HllMU) toenriched (Group II).The occurrence of these components in both on- and off-craton settingsindicates that the kimberlite source area is not strictly linked to thesuberatonic lithosphere. Mantle' plume sources are not favoured because ofthe variable source compositions and distribution of emplacement ageswithin the Province. Transitional kimberlites were derived from a sourcecomponent with mixed character, not yet noted from within the KaapvaalCraton. This is the first documented example of isotopically transitionalkimberlites from southern Africa.

[发布机构] University of the Witwatersrand