@article{ada883af13c24d4aa1871afc9f8a2c2c,
title = "Titanium isotopic fractionation in Kilauea Iki lava lake driven by oxide crystallization",
abstract = "Recent work has demonstrated that titanium (Ti) isotopes undergo mass-dependent isotope fractionation during magmatic differentiation, leaving evolved silicic melts preferentially enriched in heavy Ti isotopes. Preferential incorporation of light Ti isotopes in crystallizing Fe-Ti oxides is thought to be the mechanism responsible for this fractionation in magmatic rocks. To test this hypothesis, we present Ti isotope measurements of Fe-Ti oxide mineral separates of Kilauea Iki lava lake samples. We find that the Ti in Fe-Ti oxides is isotopically light while Ti in the residual melt and minerals is isotopically heavy. This result is consistent with the results of density functional theory (DFT) calculations in other studies, which show progressive heavy isotope enrichment for Ti from 6-fold, 5-fold, through 4-fold coordinated minerals. We therefore conclude that Ti isotopes in silicate melts undergo isotope fractionation during the crystallization of Fe-Ti oxides because Ti in oxides is primarily in 6-fold coordination whereas Ti in silicate melts is in 5- or 4-fold coordination (Ti in more evolved magmas tends to be in lower coordination). Based on our mineral separate results, we estimate the fractionation factor at 1000 °C between silicate and oxide Δ49Tisilicate-oxide to be 0.39 ± 0.06‰. This result is consistent with the fractionation factors inferred in previous studies based on Ti isotopic analyses and modeling of bulk rock measurements. We use this fractionation factor and the fractionation factors proposed by previous workers in Rhyolite MELTS to model the δ49Ti evolution of plume lavas. We find the model to generally predict the fractionations observed in Kilauea Iki, as well as the fractionations previously observed in volcanics from Hekla, Iceland and Afar, East Africa.",
keywords = "Magma differentiation, Stable isotopes",
author = "Johnson, {Aleisha C.} and Aarons, {Sarah M.} and Nicolas Dauphas and Nie, {Nicole Xike} and Hao Zeng and Helz, {Rosalind T.} and Romaniello, {Stephen J.} and Anbar, {Ariel D.}",
note = "Funding Information: We are grateful for the cooperation of the Department of Mineral Sciences, Smithsonian Institution which loaned the Kilauea Iki lava lake core samples for this study. We would like to thank our funding sources, which include FESD ?Dynamics of Earth System Oxygenation? (NSF EAR 1338810 to Anbar), NASA Earth and Space Science Fellowship awarded to Johnson (80NSSC17K0498), the NASA Astrobiology Institute under Cooperative Agreement No. NNA15BB03A issued through the Science Mission Directorate (to Lyons). ND, SA, HZ, and NN were supported by NASA grants NNX17AE86G (LARS), NNX17AE87G (Emerging Worlds), and 80NSSC17K0744 (Habitable Worlds). SJR acknowledges support from NSF Sedimentary Geology and Paleobiology (NSF EAR 1733598 to Romaniello) and the NASA Exobiology Program (80NSSC19K0474 to Romaniello). We would like to thank the Group 18 Laboratories at ASU and their staff for allowing us to use their mineral separation equipment, Fangzhen Teng for powdered samples and informative discussions, and the EPIC lab at ASU (PI Christy Till) for helpful discussions regarding the interpretation of the data. We would also like to thank Julie Prytulak, Paolo Sossi, Alex McCoy-West, and Curtis Williams for providing constructive reviews which significantly strengthened this manuscript. Funding Information: We are grateful for the cooperation of the Department of Mineral Sciences, Smithsonian Institution which loaned the Kilauea Iki lava lake core samples for this study. We would like to thank our funding sources, which include FESD “Dynamics of Earth System Oxygenation” (NSF EAR 1338810 to Anbar), NASA Earth and Space Science Fellowship awarded to Johnson (80NSSC17K0498), the NASA Astrobiology Institute under Cooperative Agreement No. NNA15BB03A issued through the Science Mission Directorate (to Lyons). ND, SA, HZ, and NN were supported by NASA grants NNX17AE86G (LARS), NNX17AE87G (Emerging Worlds), and 80NSSC17K0744 (Habitable Worlds). SJR acknowledges support from NSF Sedimentary Geology and Paleobiology (NSF EAR 1733598 to Romaniello) and the NASA Exobiology Program (80NSSC19K0474 to Romaniello). We would like to thank the Group 18 Laboratories at ASU and their staff for allowing us to use their mineral separation equipment, Fangzhen Teng for powdered samples and informative discussions, and the EPIC lab at ASU (PI Christy Till) for helpful discussions regarding the interpretation of the data. We would also like to thank Julie Prytulak, Paolo Sossi, Alex McCoy-West, and Curtis Williams for providing constructive reviews which significantly strengthened this manuscript. Publisher Copyright: {\textcopyright} 2019 Elsevier Ltd",
year = "2019",
month = nov,
day = "1",
doi = "10.1016/j.gca.2019.08.022",
language = "English (US)",
volume = "264",
pages = "180--190",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",
}