S2: Water Rock Interaction (Special Session)

[S2-04] Oxygen isotope speedometry in garnet recording fluid-rock interaction during high-temperature metamorphism

*Fumiko Higashino^1,2, Daniela Rubatto^2,3, Tetsuo Kawakami⁴, Anne-Sophie Bouvier³, Lukas P Baumgartner³ (1. OUS, 2. UNIBE, 3. UNIL, 4. Kyoto Uni.)

Keywords:oxygen isotope, garnet, SIMS, brine, granulite

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 (P) and large δ¹⁸O variations from the P-rich core to the P-poor rim. Fitting of the ¹⁸O/¹⁶O data, which gradually decreases from the core to the rim, to the diffusion equation constrains a duration of the high-T event to c. 0.5–40 Myr after the garnet rim formation.