No abstract

Oxygen fugacity (ƒO 2 ) 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 f O 2 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 ƒO 2 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 fO 2 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 f O 2 for the possible instability of diamonds in the study area remains uncertain.

particular, I'd like to thank Marcos and Leandro, who have helped me innumerous times with the mineral chemistry analyses-thank you for all your support and consideration. Thanks to the wonderful people who welcomed me so dearly at the IGc-USP: professors Renato, Frederico, Excelso, Gergely, Maria Irene, and Gaston; my friends Thereza, Melina, Fabiola, Júlio, Nicholas, Camila, and Dina. Special thanks to Mariana, who was always willing to help and to respond to my emails whenever I had any question. I would like to dedicate this work to my family, for their unconditional support in every stage of my academic life. To my brother Eduardo, who was the first one to come up with the "why not geology?" idea. Thank you for giving me the best advice that I could ever have received. To my little brother Vitor, who brings so much light and love to my life. And to my mom, thank you for every single thing that you have done for me, thank you for being so understanding whenever I could not come back home: you walked me in every single step of this work and never left me alone. I love you with all my heart. Finally, I want to express my sincere appreciation to my husband, Isaac, for encouraging me to be better every day. Without you, nothing of this would be possible. Thank you for the happiness you bring to my life, and for being so patient and understanding in my many moments of anxiety. Love you to the moon and back.