Diamonds provide rare direct samples from Earth’s deep mantle, preserving tiny mineral
and fluid inclusions that record the chemical and physical conditions at depths inaccessible
by other means. These inclusions offer unique insights into mantle metasomatism, fluid
circulation, redox conditions, and the processes associated with diamond formation.
In this seminar, I will discuss how diamond-hosted inclusions can be used to investigate the
evolution of deep mantle fluids and melts beneath ancient continental cratons. I will first
introduce fluid-rich diamonds and the analytical approaches used to characterize their
microinclusions, including electron microprobe analysis, Raman spectroscopy, and laser
ablation ICP-MS. I will also present a new laser-ablation-in-water sampling method that
enables improved recovery of ablated material for trace-element and radiogenic isotope
analyses of diamond-hosted fluids.
The second part of the seminar will focus on recent work on unusual diamonds from the
Voorspoed mine (Kaapvaal craton, South Africa) that contain coexisting nickel-rich metallic
and carbonate inclusions trapped within the same growth zones. Integrated spectroscopic,
chemical, and crystallographic analyses indicate that these inclusions formed during
interaction between oxidized carbon-rich melts derived from subducted material and
reduced mantle rocks in the deep upper mantle. The observed assemblages record
transient redox reactions, redistribution of nickel between metallic and carbonate phases,
and diamond growth during metasomatism.
These observations provide rare natural evidence for redox-driven metasomatic processes
operating at depths of several hundred kilometers and demonstrate the exceptional ability
of diamonds to preserve dynamic chemical processes in Earth’s mantle. Together, the
results highlight the central role of deep mantle fluids and melts in modifying the lithosphere
and contributing to the chemical evolution of Earth’s interior.
LOCATION: TRANSP:OPAQUE URL:https://www.weizmann.ac.il/EPS/events END:VEVENT END:VCALENDAR