Thermobarometry of mantle-derived garnets and pyroxenes of Kola region (NW Russia): Lithosphere composition, thermal regime and diamond prospectivity

• Published in: Bulletin of the Geological Society of Finland
• Main Authors: D.R. Zozulya, H. O'Brien, P. Peltonen, M. Lehtonen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Society of Finland 2009
• Subjects: Kola Peninsula; lithosphere; mantle; pyrope; diopside; kimberlite; Geology; QE1-996.5; Kandalaksha; kola peninsula
• Online Access: https://doi.org/10.17741/bgsf/81.2.003; https://doaj.org/article/d4019db92f71494d9a9adb114820c770

More than 700 pyrope, chrome diopside and chromite grains recovered from Quaternary sediments of the Kola craton, and from the Ermakovsky kimberlite in the Terskii Coast field were analyzed in order to determine their P-T parameters. Ni-thermometry on pyropes from SE Kola gives a range of temperatures between 650–1250 °C, corresponding to a sampling interval of c. 75–190 km. Pyrope compositions imply a stratified structure to the SE Kola lithospheric mantle, with G10-pyropes absent in the shallow mantle (75–110 km) where the bulk of the G9-pyropes are sourced, while a deeper mantle horizon, between 110 and 190 km, has contributed abundant G10-pyropes. Approximately 16 % of all these pyropes are derived from the diamond stability field. The Ni-temperatures of garnets from the Ermakovsky kimberlite reveal a relatively shallow sampling interval of the mantle (c. 75–140 km), dominantly within the graphite-stability field. P-T values for peridotitic chrome diopsides imply that most grains from SE Kola were derived from the graphite stability field, apparently originating from non-diamondiferous alkaline-ultramafic dykes. Nevertheless, c. 15 % of SE Kola diopsides have been derived from the stability field of diamond. Diopsides from SW Kola mostly plot in the diamond stability field. 20 % of diopsides from central Kola are derived from the diamond stability field, whereas diopsides from northern Kola region all fall within the stability field of graphite. The maximum depth of diopside xenocryst sampling varies from up to 200 km in SE and SW Kola, to 170 km in central Kola, and only to 140 km in the northern Kola region. The P-T values for chrome diopsides imply significant regional differences in heat flow: 38–44 mW/m2 within the southern part of Kola adjacent to the Kandalaksha graben; 35–38 mW/m2 towards the SE and SW away from the graben; 38–44 mW/m2 in central Kola; and up to 50 mW/m2 in northernmost Kola. These data indicate that the more “cratonic” SE, SW and likely central parts of the Kola region have higher ...