1. Clues from ab initio calculations on titanium isotopic fractionation in tholeiitic and calc-alkaline magma series
- Author
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Timo Hopp, Nicolas Dauphas, Hao Zeng, N. X. Nie, S. M. Aarons, Nicolas D. Greber, Aleisha C. Johnson, Marc Blanchard, Department of the Geophysical Sciences, University of Chicago, Scripps Institution of Oceanography (SIO - UC San Diego), University of California [San Diego] (UC San Diego), University of California (UC)-University of California (UC), Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Carnegie Institution for Science, Universität Bern [Bern] (UNIBE), Scripps Institution of Oceanography (SIO), University of California-University of California, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Carnegie Institution for Science [Washington], and Universität Bern [Bern]
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Analytical chemistry ,Fractionation ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,Isotope fractionation ,Geochemistry and Petrology ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,550 Earth sciences & geology ,Titanite ,titanium ,isotopes ,0105 earth and related environmental sciences ,fractional crystallization ,Diopside ,Fractional crystallization (geology) ,Chemistry ,Calc-alkaline magma series ,ab initio ,Silicate ,Space and Planetary Science ,visual_art ,engineering ,visual_art.visual_art_medium ,isotopic fractionation ,Igneous differentiation ,[SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy - Abstract
International audience; Magmatic differentiation produces positive correlations between δ49Ti and SiO2. The equilibrium Ti isotope fractionation factors of Ti-bearing minerals are essential for understanding the mechanisms driving this isotopic fractionation. We present ab initio-derived mean force constants of Ti-bearing minerals (barium orthotitanate, potassium titanium oxide, fresnoite, diopside, geikielite, karrooite, titanite, pseudobrookite, anatase, and titanium oxide) based on density functional theory (DFT) to calculate equilibrium isotopic fractionation factors. We find that the main driver for Ti isotopic fractionation is its coordination, with four-, five-, and sixfold-coordinated Ti characterized by mean force constants of 547, 462, and 310 N/m, respectively. The coordination number of Ti in silicate melts is thought to be lower than in minerals, driving magmas toward higher δ49Ti values by fractional crystallization. The mineral-melt fractionation factors allow modeling of the observed Ti isotope trends in tholeiitic and calc-alkaline rocks. Our model results indicate that to first order, the steeper δ49Ti trend observed in tholeiitic versus calc-alkaline magmas is most likely due to enhanced removal of Ti into sequestered minerals at low SiO2 concentration in tholeiitic series compared to calc-alkaline series. The δ49Ti–SiO2 differentiation trends, however, depend on Ti coordination in the melt and the strengths of Ti bonds in diverse Fe- and Ti-oxides, which are still uncertain. Our results show that Ti isotopes can be used to reconstruct the crystallization history and identify the magmatic series parentage of magmas that otherwise lack context, but further work is needed to identify the drivers behind Ti isotopic fractionation in igneous rocks.
- Published
- 2021
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