Oxygen isotope speedometry in granulite facies garnet recording fluid/melt–rock interaction (Sør Rondane Mountains, East Antarctica)

• Published in: Journal of Metamorphic Geology
• Main Authors: Higashino, Fumiko, Rubatto, Daniela, Kawakami, Tetsuo, Bouvier, Anne‐Sophie, Baumgartner, Lukas P.
• Other Authors: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Japan Society for the Promotion of Science
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: East Antarctica; Sør Rondane Mountains; Sør-Rondane; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1111/jmg.12490; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jmg.12490; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jmg.12490

Abstract In situ analysis of a garnet porphyroblast from a granulite facies gneiss from Sør Rondane Mountains, East Antarctica, reveals discontinuous step‐wise zoning in phosphorus and large δ 18 O variations from the phosphorus‐rich core to the phosphorus‐poor rim. The gradually decreasing profile of oxygen isotope from the core (δ 18 O = ~15‰) to the rim (δ 18 O = ~11‰) suggests that the 18 O/ 16 O zoning was originally step‐wise, and modified by diffusion after the garnet rim formation at ~800°C and 0.8 GPa. Fitting of the 18 O/ 16 O data to the diffusion equation constrains a duration of the high‐ T event (~800°C) to c . 0.5–40 Ma after the garnet rim formation. The low δ 18 O value of the garnet rim, together with the previously reported low δ 18 O values in metacarbonates, indicates regional infiltration, probably along a detachment fault, of low δ 18 O fluid/melt possibly derived from meta‐mafic to ultramafic rocks.