T164 Gem Minerals, Localities and Geological Significance

Tuesday, 24 September 2024
8:00 AM - 12:00 PM
207A

THE GROWTH HISTORY OF A SUBLITHOSPHERIC DIAMOND REVEALED BY 3D GROWTH ZONATION, INCLUSION MINERALOGY AND GEOBAROMETRY

Paper number: T164-13
Program: Technical Sessions
Time: 10:55 AM – 11:10 AM

Authors

Abstract

Earth’s plate tectonic activity drives the exchange of materials between surface and deep mantle reservoirs through time. As the only well-preserved material exhumed from transition zone and uppermost lower mantle depths, sublithospheric diamonds provide a valuable record of this activity. However, this record is often complex and can be challenging to unravel into meaningful observations. Here we examine multiple datasets from a single sublithospheric diamond from the Karowe mine, Botswana.

The diamond is a faceted, 1.5 carat, D color, type IaB gem that passed through GIA’s grading infrastructure and was later purchased for research purposes. Its inclusions comprise olivine/ringwoodite (Mg, Fe)2SiO4, ferropericlase (Mg, Fe)O, enstatite (former bridgmanite, (Mg, Fe)SiO3, and other minor phases. The mineral assemblage is consistent with a meta-peridotitic host rock near the 660 km discontinuity at the base of the mantle transition zone. This depth is independently supported by elastic geobarometry for one of the ferropericlase inclusions.

A novel hyperspectral imaging technique has been applied to this specimen to examine its 3D spatial distribution of various photoluminescent defects. This otherwise invisible spectral and textural information provides a way to visualize the growth zonation of this diamond, as well as post-growth deformation. Taken together, the data provide a clearer picture of the formation conditions of this diamond and help place it in a broader geodynamic context.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404012

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