1,3,- 1Institute of Geology and Mineralogy SB RAS, Russian Federation, Geology, NOVOSIBIRSK, 630090, Russian Federation (igor.ashchepkov@igm.nsc.ru)
- 2Saint Petersburg Mining University, Analitic Center, 21st Line 2, St. Petersburg 199106, Russia
- 3A.P. Vinogradov Institute of Geochemistry SD RAS, Favorsky str. 1A, Irkutsk, 650033, Russia,
- 4A.V. Nikolaev Institute of Inorganic Chemistry SB RAS, 630090, Novosibirsk, Lavrentieva ave, 6, Russia
Minerals from heavy concentrates from two phases of the Aykhal kimberlite pipe, Yakutia, were analyzed with the EPMA, SEM, and ICP-MS. They were used to reconstruct the mantle sections and their evolution, and to determine the features of the protokimberlite melts and melt/fluid metasomatic agents responsible for the geochemistry. A high amount of garnets belong to the dunitic type. The clinopyroxenes, as well as amphiboles, are Mg-rich and highly vary in Al, Cr, Ti, Na. Micas are Ti-biotites derived from protokimberlites. The ilmenites and chromites show domination of Mg- and Cr-rich compositions.
The mantle section of subcratonic lithospheric mantle (SCLM) for autholitic kimberlite breccia (AKB) reveals a long range of PT estimates for garnets from 8 GPa to Moho heated at the deeper part, showing in the P-Fe# plot sharp layering of 6 thick layers (subdivided to 2 sub-layers) visible by high Mg deviations and Ca fluctuations for garnets and grouping of PT points for other minerals. The lithosphere asthenosphere boundary (LAB) is marked by the ilmenite trend going from LAB to middle layer (4.5-3.5) GPa, traced by the Ti-augite and pyrope megacrysts. The minerals from tuffisitic kimberlitic breccia (TKB), show a similar division of the mantle section but amount of low-pressure pyrope and eclogite garnets is much higher.
The geochemistry of lherzolitic garnets show rounded curves of depletion in light rare earth elements (LREE) allows to subdivide them into the enriched, depleted, and common lherzolitic types. The megacrystic and low-crust garnets show higher HREE levels. The dunitic garnets reveal S-shaped, harzburgitic depressions in HMREE and curved patterns. All peridotitic garnets demonstrate U, Nb, Zr enrichment in multicomponent spider diagram (MSD). The Cr-diopsides show small U enrichment and pyroxenites with higher Th peaks Pb, Ba depressions. Ilmenites display very high Ta-Nb and Zr-Hf peaks and very low REE level except for two samples. The Cr-spinels demonstrate Ta peaks on the MSD. The phlogopites reveal Eu peaks and W-shaped REE distributions and high LILE in MSD. Diamonds show low REE levels and Pb peaks. The differences in TKB and AKB geochemistry of garnets and diopsides are in the higher level of the Th-Nb and Zr-Hf levels, showing the influence of the carbonate and H2O-bearing melts that accompanied the interactions with the protokimberlite melts.
Reconstructed with partition coefficients, parental melts reveal highly inclined lines up to 1000/PM (primitive mantle). Peridotites show U-Ba- enrichment typical for subduction related melts and high Nb also – due to super plume melts influence. Cr-diopsides and pyroxenites show dominating Th enrichment due to interaction with the carbonatite melt.
The high diamond grade of the Aykhal pipe is determined by mixing of subduction-related Na-Mn-U and peridotitic high Mg-Cr with Ti-Nb-Th plume components and hybrid melt interaction with peridotite eclogitic material with the mixing of all components.
Work was done on state assignments of IGM SB RAS FWZN-2026-0007. Russian Science Foundation Grant (24-27-00411).
How to cite: Ashchepkov, I., Logvinova, A., Ivanov, A., Sotnikova, I., and Medvedev, A.: Mineralogy and geochemistry of the xenocrysts from Aykhal kimberlite pipe, Yakutia: comparison of phases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3137, https://doi.org/10.5194/egusphere-egu26-3137, 2026.
