LA-ICP-MS U-Pb dating of rutile inclusions within corundum (ruby and sapphire): new constraints on the formation of corundum deposits along the Mozambique belt

摘要

Direct dating of corundum and the establishment of age constraints for corundum crystal growth are restricted due to the absence of a geochronometer. Syngenetic mineral inclusions may help define minimum ages for corundum growth. Here, we present results of in situ LA-ICP-MS U-Pb dating applied to rutile inclusions in corundum from localities along the Mozambique belt. U-Pb dating of rutile inclusions gave ages of 533 +/- 11 Ma (2 sigma) for the Gitonga pit (John Saul ruby mine) and 526 +/- 13 Ma for the Aqua Ruby mine, both in the Mangari area of Kenya, and an age of 499 +/- 12 Ma for ruby from the Morogoro area, Tanzania. These ages are interpreted as cooling ages that set a minimum age for corundum growth following metamorphism along the East-African Antarctic Orogen, and might be used for petrogenetic tracing of corundum in placer deposits.