Skip to content

Constraining ascent velocities of the world's youngest kimberlite magmas using diffusion chronometry modelling

Jessica. J. Rawlings1,2., Thomas, M. Gernon1., Martin, R. Palmer1., Michael, J. Stock3., Chiara, M. Petrone2., Emma, Humphreys-Williams4

  • Affiliations: 1. School of Ocean and Earth Sciences, University of Southampton, United Kingdom 2. Earth Science Department, Natural History Museum London, United Kingdom 3. Department of Geology, Trinity College Dublin, Ireland 4. Kathleen Lonsdale Building, University College London, United Kingdom

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 260

  • Programme No: 1.3.9

  • Theme 1 > Session 3

Abstract

Kimberlites are enigmatic igneous rocks which transport diamonds to Earth's surface. Despite their importance, many aspects of kimberlite volcanism remain unknown. This project aims to constrain ascent velocities of kimberlite magmas using diffusion chronometry. We analyze lavas from the youngest known kimberlites, the Igwisi Hills Volcanoes. Microanalytical work has revealed 3 olivine populations in the lavas. Olivine-I are ellipsoidal, > 1000 µm and have a Mg-rich core derived from mantle peridotite. Olivine-IIa crystals are subhedral-euhedral, < 1000 µm, and also have an Mg-rich peridotite core. Olivine-IIb crystals have a similar size and morphology to olivine-IIa crystals but possess an Fe-rich core, likely to be derived from sheared peridotite. Crystals from all populations also feature four magmatic zones (internal zones, rims, rinds & outermost rinds). Al-in-olivine thermo-barometry reveals a range of core equilibration temperatures from 734-1181°C and pressures from 25.9-49 kbar. Magmatic zones have equilibration temperatures ranging from 818-912°C as revealed by olivine-spinel pairs thermometry. EBSD has been carried out on olivine crystals to determine orientations of geochemical transects. These data are being used to conduct diffusion chronometry modelling using a range of models from excel based analytical solutions to the sophisticated DFENS (Diffusion Using Finite Elements and Nested Sampling) numerical model ran in Python. Preliminary results from analytical models suggest diffusion from cores to internal zones is very slow (average 484 years) and represents storage rather than ascent. We predict timescales calculated between magmatic zones will be significantly faster and reflect the rapid ascent kimberlites are known to undergo.