Thermobarometry of diamond inclusions: Mantle structure and evolution beneath Archean cratons and mobile belts worldwide

Abstract

Thermobarometric calculations for mineral inclusions in diamonds provide a systematic comparison of P-T-fO2 conditions for different cratons and mobile belts worldwide, using a database of 4440 mineral EPMA analyses. Beneath all cratons, the cold branch of the mantle geotherm (35-32 mWm−2) relates to PT estimates for sub-calcic garnets and rare omphacitic diamond inclusions, referring to major continental growth events in Archean. High-temperature plume-related geotherms are common in Proterozoic kimberlites such as Premier, Mesozoic-Roberts Victor etc. and are common in Slave and Siberian cratons. Eclogitic and pyroxenitic pyroxenes and garnets and Fe- and Ca-enriched pyrope diamond inclusions prevail in mobile belts like Limpopo, Magondi, Ural, Khapchan and in the marginal parts of cratons (Kimberly in Australia) They refer to diamondiferous eclogite-pyroxenite lens in the mididdle parts of lithospheric mantle. Eclogitic garnets and clinopyroxenes show trends of joint decreasing Mg# and pressures due to differentiation of rising melts. Dunitic Ca pyropes giving high-pressure estimates prevail in the central parts of cratons. The PT for the chromites reflect conditions just above the lithosphere-asthenosphere boundary formed due to interaction with the hydrous plume protokimberlite melts. Archean diamond Ca-enrich pyropes inclusions from Wawa province Canada give low-temperature conditions. Inclusions from younger kimberlites in Superior and Slave, Siberian and East European cratons show complex high-temperature geotherms due to plumes influence. Peridotite garnets beneath the Amazonian craton indicate complex layering in the lithosphere base and a pyroxene layer in the middle part of mantle lithosphere. Diamond inclusions from the Kimberley Craton of Australia show the greatest variations in the temperatures and composition. The mobile belts and marginal parts of cratons are favorable for the finding of the abundant colored diamonds. The huge plume influence for hydrated and eclogite-rich mantle like in Premier, Venetia and other kimberlites brings to the formation of giant diamonds. Diamond inclusion reveal the huge variations of PT conditions formed by different agents due to long complex stories of craton deciphered using thermobarometry and trace element and isotopic geochemistry.