Coupled deep-mantle carbon-water cycle: Evidence from lower-mantle diamonds

• Published in: Innovation (New York, NY) Vol. 2; no. 2; p. 100117
• Main Authors: Wang, Wenzhong, Tschauner, Oliver, Huang, Shichun, Wu, Zhongqing, Meng, Yufei, Bechtel, Hans, Mao, Ho-Kwang
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 28.05.2021; Cell Press; Elsevier
• Subjects: deep mantle; diamond; first-principles calculations; GEOSCIENCES; water and carbon cycle; diamond; deep mantle; water and carbon cycle; first-principles calculations
• ISSN: 2666-6758; 2666-6758
• DOI: 10.1016/j.xinn.2021.100117

Diamonds form in a variety of environments between subducted crust, lithospheric and deep mantle. Recently, deep source diamonds with inclusions of the high-pressure H2O-phase ice-VII were discovered. By correlating the pressures of ice-VII inclusions with those of other high-pressure inclusions, we assess quantitatively the pressures and temperatures of their entrapment. We show that the ice-VII-bearing diamonds formed at depths down to 800 ± 60 km but at temperatures 200–500 K below average mantle temperature that match the pressure-temperature conditions of decomposing dense hydrous mantle silicates. Our work presents strong evidence for coupled recycling of water and carbon in the deep mantle based on natural samples. [Display omitted] •A novel approach was developed to assess the pressure-temperature conditions of entrapment of inclusions in diamonds•The viscoelastic relaxation of diamond has a significant effect on the evolution of pressure and temperature•Ice-VII-bearing diamonds have formed in wet, cool environments at depths down to 800 km•The coupled recycling of water and carbon is present in the deep mantle