skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, December 13 until 2:00 AM ET on Saturday, December 14 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


This content will become publicly available on March 1, 2025

Title: Ce and Eu anomalies in zircon as indicators of oxygen fugacity in subsolidus systems
Quantifying the oxygen fugacity (fo2) of high temperature lithospheric fluids, including hydrothermal systems, presents a challenge because these fluids are difficult to capture and measure in the same manner as quenched glasses of silicate melts. The chemical properties of fluids can however be inferred through mineral proxies that interacted with the fluids through precipitation or recrystallization. Here, we present hydrothermal experiments to quantify the partition coefficients of rare earth elements (REEs) – including redox-sensitive Ce and Eu – between zircon and fluid. Experiments were conducted in a piston cylinder device at temperatures that range from 1200 to 800 ◦C under fo2-buffered conditions in a SiO2-ZrO2-NaCl-REE-oxide system, and similar experiments were performed in the absence of NaCl (31 total experiments). The fo2 was buffered to values that range from approximately 3 log units below to 7 log units above the fayalite magnetite quartz equilibrium. Zircon REE concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry whereas the quenched fluids were extracted and measured by solution-based inductively coupled plasma mass spectrometry. Zircon Ce anomalies, quantified relative to La and Pr, exhibit sensitivity to oxygen fugacity and temperature and our preferred calibration is: log [􀀀 Ce Ce* ) D 􀀀 1 ] = (0.237 ± 0.040)× log(fo2) + 9437±640 T(K) 􀀀 5.02 ± 0.38 where the Ce anomalies are calculated from the partition coefficients for La, Ce, and Pr. Zircon Eu anomalies are also a function of oxygen fugacity though they exhibit no systematic dependence on T. Our preferred calibration is described by: 􀀀 Eu Eu* ) D = 1 1+100.30±0.04􀀀 [0.27±0.03]×ΔFMQ We performed additional calculations, in which lattice strain parabolas were fit to all non-redox sensitive rare earth elements that were added to the starting composition (i.e., La, Pr, Sm, Gd, Dy, Ho, Tm, Lu) as an alternate means to calculate anomalies. This method yields broadly similar results, though we prefer the La-Pr calibrations due to the non-systematic REE patterns frequently encountered with hydrothermal zircons; e.g., LREE zircon enrichment relative to other REEs. These experiments are applied to quantify the fo2 of fluids during mineralization of critical element-bearing systems, and separately to calculate the oxygen fugacity values of fluids formed during plate boundary processes.  more » « less
Award ID(s):
1751903
PAR ID:
10511593
Author(s) / Creator(s):
; ; ;
Corporate Creator(s):
Editor(s):
Charlier, B
Publisher / Repository:
Elsevier (GCA)
Date Published:
Journal Name:
Geochimica et Cosmochimica Acta
Edition / Version:
1
Volume:
369
Issue:
C
ISSN:
0016-7037
Page Range / eLocation ID:
93 to 110
Subject(s) / Keyword(s):
Oxygen fugacity Ce anomaly Eu anomaly Critical minerals Hydrothermal fluids
Format(s):
Medium: X Size: 2 Other: pdf
Size(s):
2
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ( , Chemical Geology)
    Romano, C (Ed.)
    Monazite and xenotime are common metamorphic phases that may be reliably U/Th-Pb dated to obtain absolute ages. The utility of these minerals is significantly enhanced if a crystallization thermometer can be developed and applied to better establish the temperature-time (T-t) paths of crustal terranes. Here we report experiments in which we have modeled the T-dependent Rare Earth element (REE) cationic exchange between coexisting monazite and xenotime to derive a new thermometer. We present a thermometer in which phosphates were cocrystallized from 1150 ◦C to 850 ◦C at 1 GPa in a Y-REE-P2O5-NaCl-H2O system, with oxygen fugacity buffered at the Ni-NiO equilibrium. The composition of the phosphates was quantified using a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). Results reveal strong correlations between log10 (Π XLREE Xnt ×XY Π Mzt XLREE Mzt ×XY Mzt ) (at. %) and 104/T(K) and our preferred calibration is: log (ΠXLREE Xnt × XY Π Mzt XLREE Mzt × XY Mzt ) = ( 􀀀 6714 ± 2264) T (K) 􀀀 (0.79±1.76) where LREE = La, Ce and Pr, α = activity of a cation in a phase, and ΠαY/REE Mzt/Xnt refers to the product of activities of Y and/or REEs in a phosphate phase. The errors are 2 s.e. The greatest strength of this thermometer is its versatility. One can obtain derivative thermometers based on select elements rather than the entire suite of REEs. We showcase our thermometer’s adaptability by applying it to two studies that have published REE data on monazite and xenotime from some quartzo-feldspathic psammites and garnet-bearing pelites that experienced amphibolite facies metamorphism from the Naver nappe in the Northern Highlands Terrane, Scotland. The main calibration shown above, as well as four derivative single-element thermometers (Y, La, Ce and Pr) were applied to the first study. Upon applying these thermometers, we find that the calculated metamorphic Ts agree well with the regional metamorphic facies. Thus, this versatile thermometer can be used in geologic environments where monazite and xenotime co-crystallized. 
    more » « less
  2. ; ; ; ; ; ( , American Mineralogist: Journal of Earth and Planetary Materials)
    Abstract Partition coefficients for rare earth elements (REEs) between apatite and basaltic melt were determined as a function of oxygen fugacity (fO2; iron-wüstite to hematite-magnetite buffers) at 1 bar and between 1110 and 1175 °C. Apatite-melt partitioning data for REE3+ (La, Sm, Gd, Lu) show near constant values at all experimental conditions, while bulk Eu becomes more incompatible (with an increasing negative anomaly) with decreasing fO2. Experiments define three apatite calibrations that can theoretically be used as redox sensors. The first, a XANES calibration that directly measures Eu valence in apatite, requires saturation at similar temperature-composition conditions to experiments and is defined by: ( E u 3 + ∑ E u ) Apatite  = 1 1 + 10 - 0.10 ± 0.01 × l o g ⁡ ( f o 2 ) - 1.63 ± 0.16 . The second technique involves analysis of Sm, Eu, and Gd in both apatite and coexisting basaltic melt (glass), and is defined by: ( Eu E u * ) D Sm × Gd = 1 1 + 10 - 0.15 ± 0.03 × l o g ⁡ ( f o 2 ) - 2.46 ± 0.41 . The third technique is based on the lattice strain model and also requires analysis of REE in both apatite and basalt. This calibration is defined by ( Eu E u * ) D lattice strain = 1 1 + 10 - 0.20 ± 0.03 × l o g ⁡ ( f o 2 ) - 3.03 ± 0.42 . The Eu valence-state partitioning techniques based on (Sm×Gd) and lattice strain are virtually indistinguishable, such that either methodology is valid. Application of any of these calibrations is best carried out in systems where both apatite and coexisting glass are present and in direct contact with one another. In holocrystalline rocks, whole rock analyses can be used as a guide to melt composition, but considerations and corrections must be made to either the lattice strain or Sm×Gd techniques to ensure that the effect of plagioclase crystallization either prior to or during apatite growth can be removed. Similarly, if the melt source has an inherited either a positive or negative Eu anomaly, appropriate corrections must also be made to lattice strain or Sm×Gd techniques that are based on whole rock analyses. This being the case, if apatite is primary and saturates from the parent melt early during the crystallization sequence, these corrections may be minimal. The partition coefficients for the REE between apatite and melt range from a maximum DEu3+ = 1.67 ± 0.25 (as determined by lattice strain) to DLu3+ = 0.69 ± 0.10. The REE partition coefficient pattern, as observed in the Onuma diagram, is in a fortuitous situation where the most compatible REE (Eu3+) is also the polyvalent element used to monitor fO2. These experiments provide a quantitative means of assessing Eu anomalies in apatite and how they be used to constrain the oxygen fugacity of silicate melts. 
    more » « less
  3. ; ; ( , Goldschmidt)
    Rare earth element (REE) deposits are found in association with carbonatite and alkaline systems, where metasomatism plays a significant role in the late-stage transport and enrichment of REE [1]. Fluorite is a common gangue mineral in these mineral deposits and can incorporate varying REE concentrations by substitutions of REE3+ for Ca2+. Fluorite-hosted fluid inclusions contain significant REE concentrations [2], providing a potential record of the hydrothermal ore-forming fluids. The fluorite-fluid REE partitioning mechanisms, however, are largely unknown. To date, only one study [3] measured the partitioning of REE between fluorite and aqueous fluid at 60 °C. Here, we evaluate these REE partitioning mechanisms by combining laboratory experiments with characteristics of natural fluid inclusions that provide a range of salinities and homogenization temperatures relevant to natural systems. Batch-type experiments will be conducted between 100 and 250 °C in Teflon-lined reactors, in which millimeter-sized natural fluorite crystals (Cooke’s Peak, New Mexico) will be reacted with fluids of varying initial REE concentration, pH, and salinity. Kinetic experiments were carried out at 150 °C to test for attainment of a steady state between the fluorite crystals and the aqueous solutions. The reacted fluorite crystals will be studied using SEM, CL and EMPA. Major cations and anions in the quenched fluids will be analyzed using IC and ICP-OES; REE will be determined using solution ICP-MS. These results will permit deriving REE fluorite-fluid partition coefficients. Fluid inclusions in hydrothermal fluorite veins from the fluorite-bastnäsite REE deposits in the Gallinas Mountains in New Mexico are studied to constrain temperatures, salinities, and REE concentrations of hydrothermal ore-forming fluids in alkaline systems. Fluid inclusion assemblages were identified in growth zones and will be further studied using microthermometry. Previous studies found maximum temperatures of 400 °C in sulfate-rich NaCl-KCl brines [4]. The goal will be to link partition coefficients derived from the experiments to the REE partitioning behavior found in the natural fluorite. [1] Gysi et al. (2016), Econ. Geol. 111, 1241-1276; [2] Vasyukova and Williams-Jones (2018) Chem. Geol. 483, 385-396; [3] van Hinsberg et al. (2010), Geology 38, 847-850; [4] Williams-Jones et al. (2000), Econ. Geol. 95, 327-341. 
    more » « less
  4. ; ; ; ; ; ; ( , Geochimica et Cosmochimica Acta)
    Rhabdophane is a hydrous phosphate that commonly replaces monazite as a weathering product in critical mineral deposits during the alteration of rare earth elements (REE) bearing carbonatites and alkaline igneous complexes. It is an important host to the light (L)REE (i.e., La to Gd) but the stability and structure of binary solid solutions between the Ce and the other LREE endmembers have not yet been determined experimentally. Here we present room temperature calorimetric experiments that were used to measure the enthalpy of precipitation of rhabdophane (Ce1−xREExPO4·nH2O; REE = La, Pr, Nd, Sm, Eu, and Gd). The solids were characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and the role of water in the rhabdophane structure was further determined using thermogravimetric analysis coupled with differential scanning calorimetry. The calorimetric experiments indicate a non-ideal behavior for all of the binary solid solutions investigated with an excess enthalpy of mixing (ΔHex) described by a 2- to 3-term Guggenheim parameters equation. The solid solutions were categorized into three groups: (1) binary Ce-La and Ce-Pr which display positive ΔHex values with a slight asymmetry; (2) binary Ce-Nd and Ce-Sm which display negative ΔHex values with a nearly symmetric shape; (3) Ce-Eu and Ce-Gd which display both negative and positive ΔHex values with nearly symmetric shape. The excess Gibbs energy (ΔGex) of the solid solutions was further investigated using a thermodynamic analysis approach of aqueous-solid solution equilibria and the optimization programs GEMS and GEMSFITS. The resulting ΔGex values combined with the calorimetric ΔHex values indicate that there is likely an excess entropy contribution implying important short-range structural modifications in the solid solutions dependent on the deviation of the REE ionic radii from the size of Ce3+. These observations corroborate with the trends in the Raman v1 stretching bands of the PO4-site. The excess molar volumes determined from X-ray diffraction analysis further indicate an overall asymmetric behavior in all of the studied binary solid solutions, which becomes increasingly important from La to Gd. The pronounced short-range order–disorder occurring in groups 2 and 3 solid solutions mimics some of the behavior observed from previous studies in anhydrous monazite solid solutions. This study highlights the potential to use the chemistry and the structural modifications of rhabdophane as potential indicators of formation conditions in geologic systems and permits improving our modeling capabilities of REE partitioning in critical minerals systems. 
    more » « less
  5. ; ; ; ( , Earth and Planetary Science Letters)
    Trace element concentrations and ratios in zircon provide important indicators of the petrological processes that operate in igneous and metamorphic systems. In granitoids, the compositions of zircon have been linked to the behaviour of garnet and plagioclase—pressure-sensitive minerals—in the source during partial melting. This has led to the proposal that Europium anomalies in detrital zircon are linked to the depth of crustal melting or magmatic differentiation and are a proxy for average crustal thickness. In addition to the mineral assemblage present during partial melting, Eu anomalies in zircon are also sensitive to redox conditions as well as magma evolution during extraction, ascent, and emplacement. Here we quantitatively model how rock type, mineral assemblages, redox changes, and reaction sequences influence Eu anomalies of zircon in equilibrium with silicate melt. Partial melting of metasedimentary rocks and metabasites yields felsic to intermediate melts with a large range of Eu anomalies, which do not correlate simply with pressure (i.e. depth) of melting. Europium anomalies of zircon associated with partial melting of metasedimentary rocks are most sensitive to temperature whereas Eu anomalies associated with metabasite melting are controlled by plagioclase proportion—a function of pressure, temperature, and rock composition—as well as changes in oxygen fugacity. Furthermore, magmatic crystallization of granitoids can increase or decrease Eu anomalies in zircon from those of the initial (anatectic) melt. Therefore, Eu anomalies in zircon should not be used as a proxy for the crustal thickness or depth of melting but can be used to track the complex processes of metamorphism, partial melting, and magmatic differentiation in modern and ancient systems. Secular changes of Eu/Eu* from the zircon archive may reflect a change in thermal gradients of crustal melting or an increase in the reworking of sedimentary rocks over time. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email