New Mineral From Earth’s Lower Mantle Found in a Diamond

A diamond that has crystals of davemaoite inside it. Credit: Aaron Celestian, Natural History Museum of Los Angeles County.

A polymorph of calcium silicate (CaSiO3) having the perovskite structure is expected to be stable at the pressures and temperatures of Earth’s transition zone and lower mantle (420–2700 kilometers deep) and could be a key phase in determining Earth’s heat budget and distribution. Calcium silicate perovskite has been synthesized experimentally and shown to be capable of hosting several of the most important radiogenic heat-producing elements, such as potassium, uranium, and thorium, which are incompatible (i.e., not easily hosted) in upper mantle minerals. However, it has been difficult to find this phase in nature because it is stable only under conditions of extremely high pressure and temperature, such as in the lower mantle.

A research team led by Oliver Tschauner of the University of Nevada, Las Vegas has now reported the discovery of calcium silicate perovskite as an inclusion in a diamond from the Orapa diamond mine in Botswana. Calcium silicate perovskite was approved as a new mineral by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association, and is named “davemaoite” in honor of Dave (Ho-kwang) Mao for his distinguished contributions to the field of deep-mantle geophysics and petrology. Tschauner and his team characterized davemaoite within a deep-earth diamond using synchrotron X-ray diffraction, X-ray fluorescence, and laser-ablation inductively coupled plasma mass spectrometry. Structural and chemical analysis of the mineral showed that it contains significant abundances of potassium, uranium, and thorium, the main elements that have half-lives long enough to produce radioactive heat for the duration of Earth’s geologic history. The Earth’s internal heat provides the energy for driving mantle convection and tectonic plate movement. This study supports the hypothesis that davemaoite plays an essential part in heat generation and distribution in the deep mantle and affects the movement of tectonic plates. READ MORE