Oxygen fugacity of Alto Paranaíba kimberlites and diamond instability: Três Ranchos IV and Limeira I intrusions

Author(s)

Bruna Coldebella ^[1] ; Rogério Guitarrari Azzone ^[2] ; Luanna Chmyz ^[3] ; Excelso Ruberti ^[4] ; Darcy P. Svisero ^[5]

Affiliation

^[1] Universidade de São Paulo. Instituto de Geociências. Programa de Pós-Graduação Geociências (Mineralogia e Petrologia) - Brasil

^[2] Universidade de São Paulo. Instituto de Geociências. Programa de Pós-Graduação Geociências (Mineralogia e Petrologia) - Brasil

^[3] Universidade de São Paulo. Instituto de Geociências. Programa de Pós-Graduação Geociências (Mineralogia e Petrologia) - Brasil

^[4] Universidade de São Paulo. Instituto de Geociências. Programa de Pós-Graduação Geociências (Mineralogia e Petrologia) - Brasil

^[5] Universidade de São Paulo. Instituto de Geociências. Programa de Pós-Graduação Geociências (Mineralogia e Petrologia) - Brasil

• Document type: Journal article
• Source: BRAZILIAN JOURNAL OF GEOLOGY; v. 50, n. 1 2020-03-09.

Abstract

Abstract 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. (AU)

• FAPESP's process: 17/03768-8 - Xenocryst and Antecryst compositional influence in basic to ultrabasic alkaline magmas
• Grantee: Rogério Guitarrari Azzone
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/06082-6 - The Paraná-Etendeka magmatic province in Brazil: temporal and petrologic relationships between the tholeiitic and alkaline magmatism and geodynamic implications
• Grantee: Excelso Ruberti
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 16/12627-6 - Intensive parameters of crystallization (P-T-fO2) for kimberlites from the alto Paranaíba alkaline province and the diamond instability: the Três Ranchos IV e Limeira I intrusions
• Grantee: Bruna Coldebella
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 18/15731-4 - Elements mobility during fenitization processes: the carbonatite metasomatism in the Alto Paranaíba and Ponta Grossa Arch alkaline provinces
• Grantee: Luanna Chmyz
• Support Opportunities: Scholarships in Brazil - Post-Doctoral