Experimental calibration of a new oxybarometer for silicic magmas based on vanadium partitioning between magnetite and silicate melt
Introduction
Oxygen fugacity (fO2) is an important parameter in magmatic systems that affects the stability of mineral phases and fluid species (Lindsley and Frost, 1992, Keppler, 1993, Jugo et al., 2010). Furthermore, it affects mineral-melt and fluid-melt partition coefficients of many metals (Candela and Bouton, 1990, Taylor and Wall, 1992, Peiffert et al., 1994, Linnen et al., 1996, Jugo et al., 1999) and thus the mineralizing potential of intrusions (Ishihara, 1981, Lehmann, 1990, Blevin et al., 1996).
The most commonly applied method to constrain oxygen fugacity in intermediate to silicic rocks is Fe-Ti oxide thermobarometry (e.g. Buddington and Lindsley, 1964, Carmichael, 1967, Stormer, 1983, Andersen and Lindsley, 1988, Ghiorso and Sack, 1991, Lattard et al., 2005, Ghiorso and Evans, 2008). Other approaches are based on mineral reactions involving olivine, pyroxene, and/or sphene (Frost and Lindsley, 1992, Lindsley and Frost, 1992, Andersen et al., 1993, Xirouchakis et al., 2001), or biotite, K-feldspar and magnetite (Wones and Eugster, 1965, Wones, 1981). Most recently, oxygen fugacity has been estimated also from amphibole compositions (Ridolfi et al., 2009).
However, despite the various techniques listed above, reconstruction of magmatic fO2 in Si-rich igneous rocks remains a challenging task, particularly in the case of intrusive rocks. There are only few intrusive rocks that contain unaltered assemblages of the above mentioned minerals, because in most cases the minerals were either destroyed or reset at subsolidus conditions, such that fO2 estimation is either not possible anymore or leads to erroneous results. Furthermore, many samples contain only one Fe-Ti-oxide phase (magnetite or ilmenite), preventing application of the classical magnetite–ilmenite oxybarometry. The main goal of this study was to develop an oxybarometer that is based on phases which commonly occur as inclusions within quartz phenocrysts and thus were protected from subsolidus alteration. This oxybarometer can be applied to any silicic rock that contains magnetite, independent of whether or not the magma was saturated also in ilmenite.
For mineral–melt oxybarometry it is essential to focus on an element whose concentration varies as a function of oxygen fugacity in either the silicate melt or in a coexisting mineral phase, or to different extents in both. Further requirements are that the element of interest occurs in measurable amounts (i.e. above the detection limit of LA-ICP-MS measurements) in both phases, and that its concentration does not depend strongly on other factors such as mineral composition or melt composition. Previous studies have shown that vanadium partitioning between magnetite and silicate melt, DVmgt/melt, fulfills the above-mentioned requirements, and several calibrations have been developed (Irving, 1978, Horn et al., 1994, Canil, 1999, Canil, 2002, Toplis and Corgne, 2002, Righter et al., 2006a, Righter et al., 2006b, Mallmann and O'Neill, 2009). However, most of these studies focused on mafic to ultramafic systems at very high temperatures, which are not applicable to upper crustal rhyolitic magmas. The aim of the current study is to fill this gap by developing an experimental calibration of the vanadium magnetite–melt oxybarometer at P-T-x conditions that are relevant for silicic, upper crustal magmas. Such an oxybarometer would be useful not only for rocks lacking ilmenite, but also for slowly-cooled rocks such as granites because both silicate melt and to a lesser degree magnetite commonly occur as inclusions within quartz phenocrysts (e.g., Anderson et al., 2000, Audétat and Pettke, 2006, Audétat, 2015, Zhang and Audétat, 2017). If such inclusions are not intersected by later cracks and are analyzed as entities by laser-ablation ICP-MS (LA-ICP-MS), their original compositions – and thus DVmgt/melt partition coefficients and corresponding fO2 values – can be reconstructed.
Section snippets
Experimental methods
The following starting glasses were used in our experiments: (i) Synthetic haplogranite glasses with alumina saturation indices (ASI) of 0.7, 0.9 and 1.1, and (ii) natural obsidians from New Zealand, China and Armenia. The haplogranites were prepared from analytical grade SiO2, Al(OH)3, Na2CO3 and K2CO3. Their SiO2 content was fixed at the value corresponding to the 2 kbar haplogranite eutectic melt composition (Qz35Ab40Or25; Johannes and Holtz, 1996), and ASI was changed by varying Al2O3, Na2O
Analytical methods
The run products were analyzed by LA-ICP-MS using a system consisting of a GeolasPro 193 nm ArF Excimer Laser (Coherent, USA) attached to an Elan DRC-e (Perkin Elmer, Canada) quadrupole mass spectrometer. The ICP-MS was tuned to a ThO/Th rate of 0.05–0.1% and a Ca2+/Ca+ rate of 0.1–0.2% according to measurements on NIST SRM 610 glass (Jochum et al., 2011). The sample chamber was flushed with He gas at a rate of 0.4 l/min, to which 5 ml/min H2 gas was added on its way to the ICP-MS. The following
Results
Recovered samples consist of grains or clusters of magnetite embedded in optically transparent silicate glass (Fig. 2). The presence of large, isolated bubbles filled with aqueous fluid suggests that the experiments were saturated with an aqueous fluid phase, which is necessary to reach the fO2 imposed by the external buffer. Neutral pH was found in all samples, meaning that there was no CO2 (e.g. because of incomplete decarbonation of the glass), which could have changed the fO2 and the fluid
Discussion
In general, the DVmgt/melt values obtained in the present study are reproducible and vary regularly with temperature and ASI, suggesting that equilibrium was attained. Exceptions are three runs conducted at 800 °C at the Ni-NiO buffer (RA-V10c, RA-V15b,c and RA-V30b), which show an unusually large scatter (Fig. 4). In these experiments attainment of equilibrium appears to have been hindered by a combination of (1) low temperatures, (2) higher viscosity of the melt (e.g. Mysen and Toplis, 2007)
Conclusions and future perspectives
The experimental data presented in this study allowed identification of the main factors controlling vanadium partitioning between magnetite and melt in silicic magmas. DVmgt/melt is most strongly affected by fO2, changing by 1.5–1.7 log units between the Ni-NiO and MnO-Mn3O4 buffers. This result thus confirms earlier studies noting a strong dependence of vanadium partitioning on oxygen fugacity. Two other major parameters are temperature and melt composition (ASI), whereas magnetite
Acknowledgements
This research was supported by the German Science Foundation grant AU 314/5-1. We are thankful to Matteo Masotta, Hans Keppler, and Dan Frost for their useful comments and help in interpreting our data, and to Stefan Übelhack for machining tools for the experiments. Antony Burnham, John C. Ayers and two anonymous reviewers are thanked for their thorough and insightful reviews. Róbert Arató is also grateful to Miklós Arató for his help with the linear regression, as well as to Haihao Guo, Ananya
References (55)
- et al.
QUILF: a pascal program to assess equilibria among Fe–Mg–Mn–Ti oxides, pyroxenes, olivine, and quartz
Comput. Geosci.
(1993) - et al.
Melt inclusions
- et al.
The effect of dissolved water on the oxidation state of silicic melts
Geochim. Cosmochim. Acta
(1996) On the occurrence of apparent non-Henry's Law behaviour in experimental partitioning studies
Geochim. Cosmochim. Acta
(1993)Vanadium partitioning between orthopyroxene, spinel and silicate melt and the redox states of mantle source regions for primary magmas
Geochim. Cosmochim. Acta
(1999)Vanadium in peridotites, mantle redox and tectonic environments: Archean to present
Earth Planet. Sci. Lett.
(2002)- et al.
The effect of water and fO2 on the ferric–ferrous ratio of silicic melts
Chem. Geol.
(2001) - et al.
Experimentally determined partitioning of high field strength- and selected transition elements between spinel and basaltic melt
Chem. Geol.
(1994) A review of experimental studies of crystal/liquid trace element partitioning
Geochim. Cosmochim. Acta
(1978)- et al.
Magmatic sulfides and Au: Cu ratios in porphyry deposits: an experimental study of copper and gold partitioning at 850 °C, 100 MPa in a haplogranitic melt–pyrrhotite–intermediate solid solution–gold metal assemblage, at gas saturation
Lithos
(1999)
Sulfur K-edge XANES analysis of natural and synthetic basaltic glasses: implications for S speciation and S content as function of oxygen fugacity
Geochim. Cosmochim. Acta
The combined effects of fO2 and melt composition on SnO2 solubility and tin diffusivity in haplogranitic melts
Geochim. Cosmochim. Acta
Major- and trace-element magnetite–melt equilibria
Chem. Geol.
Uranium in granitic magmas: Part 1. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H2O-Na2CO3 system at 720–770 °C, 2 kbar
Geochim. Cosmochim. Acta
Partitioning of Ni, Co and V between spinel-structured oxides and silicate melts: importance of spinel composition
Chem. Geol.
The oxidation state of iron in silicic melt at 500 MPa water pressure
Chem. Geol.
Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions: controls on element partitioning
Geochim. Cosmochim. Acta
Internally consistent solution models for Fe-Mg-Mn-Ti oxides: Fe-Ti oxides
Am. Miner.
Evolution of Bishop Tuff rhyolitic magma based on melt and magnetite inclusions and zoned phenocrysts
J. Petrol.
Compositional evolution and formation conditions of magmas and fluids related to porphyry Mo mineralization at Climax, Colorado
J. Petrol.
Evolution of a porphyry-Cu mineralized magma system at Santa Rita, New Mexico (USA)
J. Petrol.
Intrusive metallogenic provinces in eastern Australia based on granite source and composition
Geol. Soc. Am. Spec. Pap.
Iron-titanium oxide minerals and synthetic equivalents
J. Petrol.
The influence of oxygen fugacity on tungsten and molybdenum partitioning between silicate melts and ilmenite
Econ. Geol.
The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesian silicates
Contrib. Mineral. Petrol.
The structural role and homogeneous redox equilibria of iron in peraluminous, metaluminous and peralkaline silicate melts
Contrib. Mineral. Petrol.
Introduction to oxygen fugacity and its petrologic importance
Rev. Mineral. Geochem.
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