Sublithospheric diamonds: Plate tectonics from Earth's deepest samples (Annual Reviews, 2024)
✦ A 3 billion year old quartz pebble conglomerate from the Jack Hills, Yilgarn Craton, Western Australia. This metasedimentary rock contains the oldest known minerals on Earth, zircons that formed only 100 million years after the Earth accreted. (photo: Steve Shirey)
✦ Plot of diamond type, E-type or eclogitic (red) vs P-type or peridotitic (green) with seismic wave velocity structure of the Kaapvaal craton at the 150 km depths where diamonds crystallize.
✦ Optical microscopy image (fov = 1.5 mm) of a shiny, elongate metallic inclusion in a diamond fragment cut from a large, gem-quality, superdeep diamond, Letseng mine, Lesotho.
✦ Elemental map by scanning electron microscopy of a polished diamond surface (black) that exposes a metallic inclusion. These metallic inclusions contain an assemblage of iron carbides, sulfides, and alloys that crystallize at low pressure upon eruption in their host kimberlite. (Left figure from Shirey et al., Science 2002. Middle and right figures from Smith et al., Science 2016).