The genesis of kimberlites and associated rocks: Strontium isotopic evidence

摘要: Abstract In this study of materials from South African kimberlite pipes a comparison was made the strontium isotope ratios for (i) total rocks (16 samples); (ii) peridotite and eclogite nodules (12 (iii) mineral concentrates above rock types, phlogopite diopside (94 mica 40 other separates, mainly pyroxenes). Complementary K, Rb Sr abundance measurements were made. Since significance results hinges on freshness samples, parameter assessed by acidleaching, petrographic electron-probe investigation. It is concluded that neither 87 86 nor content affected possible alteration in clinopyroxenes. ( ) 0 clinopyroxenes different hosts whole fresh increase following order: discrete (0.703–0.704) The values coexisting omphacites micas are different, indicating probably secondary, whereas similarity consistent with petrographically primary nature mica. sources also considered. shown garnet type analysed cannot be recent parent eclogite, can it directly parental to kimberlite. Both accidental inclusions association (unless formed very many millions years before pipe emplacement) considered fortuitous. Eclogite represented omphacite (and garnet) Discrete could have been associated source basaltic or megacrysts accidentally incorporated, perhaps low velocity zone. between isotopic certain parameters Stormberg volcanics noted.