Oxygen fugacity of Alto Paranaíba kimberlites and diamond instability: Três Ranchos IV and Limeira I intrusions
| Autor: | Darcy P. Svisero, Luanna Chmyz, Rogério Guitarrari Azzone, Bruna Coldebella, Excelso Ruberti |
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| Rok vydání: | 2020 |
| Předmět: |
QE1-996.5
010506 paleontology Geochemistry Diamond Geology intensive parameters of crystallization oxygen fugacity engineering.material 010502 geochemistry & geophysics 01 natural sciences Instability Standard deviation Mineral redox buffer engineering CRISTALIZAÇÃO General Earth and Planetary Sciences kimberlites Alto Paranaíba Province Xenolith Monticellite Kimberlite 0105 earth and related environmental sciences Perovskite (structure) |
| Zdroj: | Repositório Institucional da USP (Biblioteca Digital da Produção Intelectual) Universidade de São Paulo (USP) instacron:USP Brazilian Journal of Geology v.50 n.1 2020 Brazilian Journal of Geology Sociedade Brasileira de Geologia (SBGEO) instacron:SBGEO Brazilian Journal of Geology, Volume: 50, Issue: 1, Article number: e20190087, Published: 09 MAR 2020 Brazilian Journal of Geology, Vol 50, Iss 1 (2020) |
| Popis: | Oxygen fugacity (ƒO2) conditions were established for Três Ranchos IV (TR-IV, diamond-bearing) and Limeira I (LM-I, barren) kimberlite intrusions, in Alto Paranaíba Alkaline Province, to constrain a possible correlation between fO2 and diamond instability. Temperature and pressure estimates obtained from the xenocryst assemblage composition are compatible up to garnet lherzolite levels. It suggests that both intrusions could cross the diamond-stability field. The ƒO2 of the TR-IV constrained by perovskite oxygen barometry presents an average value of -2.4 for ΔNNO, with standard deviation of 1.30 (n = 120), whereas those calculations for LM-I have an average value of -1.31 for ΔNNO, with standard deviation of 1.38 (n = 81). Considering these uncertainties, there is an important superposition of fO2 values for both intrusions, in which there is higher tendency of more reduced conditions for TR-IV. For the LM-I, an oxybarometer based on the composition of monticellite yielded a similar ΔNNO range: -4.2 and +2.5. Some crystals and samples present trends towards more reduced conditions, while others display more oxidized conditions for each intrusion. Due to the superposition of ranges and absence of a preferential trend, the influence of fO2 for the possible instability of diamonds in the study area remains uncertain. |
| Databáze: | OpenAIRE |
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