Pristine helium from the Karoo mantle plume within the shallow asthenosphere beneath Patagonia.

Mantle xenoliths usually represent fragments derived from the depleted and degassed lithospheric mantle with He/He isotope ratios (6 ± 1 R) lower than those of mid-ocean ridge basalts (8 ± 1 R). Otherwise, basalts from oceanic islands related to hotspots often have high He/He ratios (>10 R), suggesting a deep and pristine undegassed mantle source. Here we present a striking high-He/He component (up to 27.

Dense hydrated Mg-silicates in diamond: Implications for transport of HO into the mantle.

Water in Earth's upper mantle is a minor and yet critically important component that dictates mantle properties such as strength and melting behavior. Minerals with stoichiometric water, such as those of the humite group, are important yet poorly characterized potential reservoirs for volatiles in the upper mantle. Here, we report observation of hydroxyl members of the humite group as inclusions in mantle-derived diamond.