Mantle-derived cargo vs. magmatic growth: ascent path, dynamics of the Udachnaya kimberlite and interactions with the Siberian sub-cratonic lithosphere

Unravelling the processes taking place during the genesis of kimberlites, their ascent through the sub-cratonic mantle and their emplacement in the crust is challenging, as kimberlites are mixtures of mantle-derived and magmatic components, rarely preserving pristine evidence of their original nature. Furthermore, their intense state of alteration makes it difficult to access the textural-compositional record of information engraved in the phase constituents. In this study, fresh samples of kimberlites and related mantle-derived xenocrysts-xenoliths from the Udachnaya pipe (Siberia) were investigated to reconstruct the pressure-temperature-time-composition (P-T-t-X) framework of the sub-cratonic lithosphere at the time of kimberlite emplacement. Routine and high-precision electron microprobe analyses of olivine, phlogopite and spinel from different facies of the Udachnaya pipe (intrusive coherent, hypabyssal and pyroclastic, sensu Scott Smith et al., 2013) showed that specific phase assemblages are associated with each evolutionary stage of the kimberlite. Olivine composition, in particular, is extremely variable, ranging from high-Fo and high-Ni (Fo93; NiO = 0.45 wt%) to low-Fo and low-Ni (Fo85; NiO = 0.10 wt%), but also to high-Fo and low-Ni (Fo>93; NiO <0.05 wt%) terms, often encompassing the whole compositional spectrum in a single sample and/or showing marked zoning within the individual crystals. 
A comparison between the main constituents of the Udachnaya kimberlite and those of the mantle xenoliths sampled during ascent, complemented by detailed major-trace element profiles on olivine crystals, was put forward to: (i) discriminate between the mantle-derived xenocryst cargo and the magmatic assemblage; (ii) model the P-T-fO2 path of kimberlites; (iii) speculate about their ascent rate; (iv) model the interactions between kimberlite-related fluid/melts and the Siberian sub-cratonic lithosphere.

REFERENCES
Scott Smith, B.H., Nowicki, T.E., Russell, J.K., Webb, K.J., Mitchell, R.H., Hetman, C.M., ... & Robey, J.A. (2013). Kimberlite terminology and classification. In Proceedings of 10th international kimberlite conference (pp. 1-17). Springer, New Delhi.