Compositional effects on the solubility of minor and trace elements in oxide spinel minerals: Insights from crystal-crystal partition coefficients in chromite exsolution
Por:
Colas, Vanessa, Alberto Padron-Navarta, Jose, Maria Gonzalez-Jimenez, Jose, Griffin, William L., Fanlo, Isabel, O'Reilly, Suzanne Y., Gervilla, Fernando, Proenza, Joaquin A., Pearson, Norman J., Escayola, Monica P.
Publicada:
1 may 2016
Resumen:
Chromite from Los Congos and Los Guanacos in the Eastern Pampean Ranges of Córdoba (Argentinian Central Andes) shows homogenous and exsolution textures. The composition of the exsolved phases in chromite approaches the end-members of spinel (MgAl2O4; Spl) and magnetite (Fe2+Fe23+${\text{Fe}}-2{3 + }$O4; Mag) that define the corners of the spinel prism at relatively constant Cr3+/R3+ ratio (where R3+ is Cr+Al+Fe3+). The exsolution of these phases from the original chromite is estimated to have accounted at =600 °C on the basis of the major element compositions of chromite with homogenous and exsolution textures that are in equilibrium with forsterite-rich olivine (Fo95). The relatively large size of the exsolved phases in chromite (up to ca. 200 µm) provided, for the first time, the ability to conduct in situ analysis with laser ablation-inductively coupled plasma-mass spectrometry for a suite of minor and trace elements to constrain their crystal-crystal partition coefficient between the spinel-rich and magnetite-rich phases (DiSpl/Mag$D-{\text{i}}^{{\text{Spl/Mag}}}$). Minor and trace elements listed in increasing order of compatibility with the spinel-rich phase are Ti, Sc, Ni, V, Ge, Mn, Cu, Sn, Co, Ga, and Zn. DiSpl/Mag$D-{\text{i}}^{{\text{Spl/Mag}}}$ values span more than an order of magnitude, from DTiSpl/Mag$D-{{\text{Ti}}}^{{\text{Spl/Mag}}}$ = 0.30 ± 0.06 to DZnSpl/Mag$D-{{\text{Zn}}}^{{\text{Spl/Mag}}}$= 5.48 ± 0.63. Our results are in remarkable agreement with data available for exsolutions of spinel-rich and magnetite-rich phases in other chromite from nature, despite their different Cr3+/R3+ ratio. The estimated crystal-crystal partitioning coefficients reflect the effect that crystal-chemistry of the exsolved phases from chromite imposes on all investigated elements, excepting Cu and Sc (and only slightly for Mn). The observed preferential partitioning of Ti and Sc into the magnetite-rich phase is consistent with high-temperature chromite/melt experiments and suggests a significant dependence on Fe3+ substitution in the spinel structure. A compositional effect of major elements on Ga, Co, and Zn is observed in the exsolved phases from chromite but not in the experiments; this might be due to crystal-chemistry differences along the MgFe-1-Al2Fe-23+${\text{Fe}}-{-2}^{3 + }$ exchange vector, which is poorly covered experimentally. This inference is supported by the strong covariance of Ga, Co, and Zn observed only in chromite from layered intrusions where this exchange vector is important. A systematic increase of Zn and Co coupled with a net decrease in Ga during hydrous metamorphism of chromitite bodies cannot be explained exclusively by compositional changes of major elements in the chromite (which are enriched in the magnetite component). The most likely explanation is that the contents of minor and trace elements in chromite from metamorphosed chromitites are controlled by interactions with metamorphic fluids involved in the formation of chlorite. © 2016 by Walter de Gruyter Berlin/Boston.
Filiaciones:
Colas, Vanessa:
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, Mexico City 04510, DF, Mexico
Univ Zaragoza, Dept Ciencias Tierra, Pedro Cerbuna 12, E-50009 Zaragoza, Spain
Alberto Padron-Navarta, Jose:
CNRS, Geosci Montpellier, F-34095 Montpellier, France
Univ Montpellier, UMR5243, F-34095 Montpellier, France
Maria Gonzalez-Jimenez, Jose:
Univ Chile, Dept Geol, Plaza Ercilla 803, Santiago, Chile
Univ Chile, CEGA, Plaza Ercilla 803, Santiago, Chile
Griffin, William L.:
Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst CCFS, Sydney, NSW 2109, Australia
Macquarie Univ, GEMOC Natl Key Ctr, Dept Earth & Planetary Sci, Sydney, NSW 2109, Australia
Fanlo, Isabel:
Univ Zaragoza, Dept Ciencias Tierra, Pedro Cerbuna 12, E-50009 Zaragoza, Spain
O'Reilly, Suzanne Y.:
Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst CCFS, Sydney, NSW 2109, Australia
Macquarie Univ, GEMOC Natl Key Ctr, Dept Earth & Planetary Sci, Sydney, NSW 2109, Australia
Gervilla, Fernando:
Univ Granada, Fac Ciencias, CSIC, Dept Mineral & Petrol, Avda Fuentenueva S-N, Granada 18002, Spain
Univ Granada, Fac Ciencias, CSIC, Inst Andaluz Ciencias Tierra, Avda Fuentenueva S-N, Granada 18002, Spain
Proenza, Joaquin A.:
Univ Barcelona, Fac Geol, Dept Cristallog Mineral & Diposits Minerals, Marti & Franques S-N, E-08028 Barcelona, Spain
Pearson, Norman J.:
Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst CCFS, Sydney, NSW 2109, Australia
Macquarie Univ, GEMOC Natl Key Ctr, Dept Earth & Planetary Sci, Sydney, NSW 2109, Australia
Escayola, Monica P.:
Univ Buenos Aires, Fac Ciencias Exactas & Nat, Dept Ciencias Geol, IDEAN CONICET, Intendente Guiraldes 2160,Ciudad Univ, RA-1428 Buenos Aires, DF, Argentina
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