An empirical calibration of the serpentine-water oxygen isotope fractionation at T = 25–100 °C. (1st April 2023)

• Record Type: Journal Article
• Authors: Scicchitano, Maria Rosa; de Obeso, Juan Carlos; Blum, Tyler B.; Valley, John W.; Kelemen, Peter B.; Nachlas, William O.; Schneider, William; Spicuzza, Michael J.; Wilke, Franziska D.H.; Roddatis, Vladimir
• Is Part Of: Geochimica et cosmochimica acta. Volume 346(2023)
• Page Start: 192
• Page End: 206
• Publication Date: 2023-04-01
• Subjects: Oxygen isotopes -- Equilibrium isotope fractionation -- Serpentine -- Oman -- SIMS; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2023.02.015
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The ability to precisely constrain the physical–chemical conditions of serpentinization, such as temperature and fluid source, is limited by the accuracy of calibrations for oxygen isotope fractionation between serpentine and water – i.e., 1000 lnα(serpentine-water) – which disagree by up to 20‰ when extrapolated to T < 200 °C. In this study, we present a new empirical calibration of 1000 lnα(serpentine-water) aiming to improve applications of oxygen isotope geochemistry to very low- T serpentinization ( T < 100 °C). We used the high-spatial resolution capabilities of Secondary Ion Mass Spectrometry (SIMS) to analyze oxygen isotope ratios in mineral pairs of calcite + serpentine, quartz + serpentine and talc + serpentine co-crystallized at scales ≤ 50 μm in six serpentinite samples from the Samail ophiolite (Oman). SIMS analysis shows that the mineral pairs are relatively homogenous in oxygen isotope ratios with variability in δ 18 O values ≤2‰ (2 s). Clumped isotope thermometry and petrological constraints indicate crystallization temperatures from 25 to 100 °C for the investigated samples. These independent constraints on temperature allowed us to derive 1000 lnα(serpentine-water) by combining Δ 18 O(quartz-serpentine), Δ 18 O(talc-serpentine) and Δ 18 O(calcite-serpentine) measured by SIMS in the investigated samples with Δ 18 O(quartz-water), Δ 18 O(talc-water) and Δ 18 O(calcite-water) calibrations available in the literature. Our empirical calibration of 1000 lnα(serpentine-water) = 1.04 ± 0.20 (2SE) × 10 6 / T 2 ( T in K), from T = 25 to 100 °C, is within uncertainty of former high-temperature empirical calibrations extrapolated to T < 100 °C and matches experimental calibrations when extrapolated to T = 250 °C. The new serpentine-water calibration enables more accurate reconstructions of fluid-rock interactions occurring during low-temperature serpentinization processes in various tectonic settings.