2022
|
Florin, G., Alard, O., Luais, B., Rushmer, T. Abundances of siderophile elements in H-chondrite metal grains: Implications for the origin of metal in unequilibrated ordinary chondrites (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 341, p. 1–15, 2022. @article{Florin_etal2022,
title = {Abundances of siderophile elements in H-chondrite metal grains: Implications for the origin of metal in unequilibrated ordinary chondrites},
author = {G. Florin and O. Alard and B. Luais and T. Rushmer},
doi = {10.1016/j.gca.2022.11.014},
year = {2022},
date = {2022-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {341},
pages = {1--15},
abstract = {Understanding the evolution of metal in the protoplanetary disk is necessary to constrain the first steps of metal-silicate segregation and the early stages of the evolution of the protoplanetary disk. We measured the siderophile elemental compositions (PGE, Ni, Co, Fe, Cu, Ga, Ge) of individual metal grains in H ordinarychondrites by laser ablation inductively coupled plasma mass spectrometry to investigate their formation. We analyzed unequilibrated ordinary chondrites (H3) to constrain processes affecting the metal before accretion, and inferred the effects of metamorphism by comparing their elemental compositions to those of equilibrated chondrites (H4--H6). Our results highlight large variations of refractory (Re, Os, W, Ir, Ru, Mo, Pt) and moderately volatile siderophile element (Pd, Au, Ga, Ge) concentrations among metal grains in H3 samples that permit to classify them according to their Ge/Ir ratios and HSE contents. These intergrain variations are progressively homogenized in H4--H6 samples due to their increasing degrees of metamorphism. To constrain the origin of the metal, we modeled its evolution during melting and crystallization. Our melting model of a single metallic precursor containing 1.5 wt% C and up to 12 wt% S reproduces well the observed range of siderophile element compositions in the metal. Metal grains show a range of W, Mo, and Ga compositions that we interpret to reflect various local (grain-scale) oxidation states during the melting event(s) due to the heterogeneous distribution of various oxidizing components within the precursors. The very similar HSE compositions of H and L/LL metal grains suggests that the variations of bulk metal abundance and HSE concentrations observed among the different classes of ordinary chondrites (H, L, LL) result from the heterogeneous physical distribution of a relatively chemically homogeneous metal component among OC parent bodies, and not from a chemical (sensu lato) gradient between H and LL chondrites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Understanding the evolution of metal in the protoplanetary disk is necessary to constrain the first steps of metal-silicate segregation and the early stages of the evolution of the protoplanetary disk. We measured the siderophile elemental compositions (PGE, Ni, Co, Fe, Cu, Ga, Ge) of individual metal grains in H ordinarychondrites by laser ablation inductively coupled plasma mass spectrometry to investigate their formation. We analyzed unequilibrated ordinary chondrites (H3) to constrain processes affecting the metal before accretion, and inferred the effects of metamorphism by comparing their elemental compositions to those of equilibrated chondrites (H4--H6). Our results highlight large variations of refractory (Re, Os, W, Ir, Ru, Mo, Pt) and moderately volatile siderophile element (Pd, Au, Ga, Ge) concentrations among metal grains in H3 samples that permit to classify them according to their Ge/Ir ratios and HSE contents. These intergrain variations are progressively homogenized in H4--H6 samples due to their increasing degrees of metamorphism. To constrain the origin of the metal, we modeled its evolution during melting and crystallization. Our melting model of a single metallic precursor containing 1.5 wt% C and up to 12 wt% S reproduces well the observed range of siderophile element compositions in the metal. Metal grains show a range of W, Mo, and Ga compositions that we interpret to reflect various local (grain-scale) oxidation states during the melting event(s) due to the heterogeneous distribution of various oxidizing components within the precursors. The very similar HSE compositions of H and L/LL metal grains suggests that the variations of bulk metal abundance and HSE concentrations observed among the different classes of ordinary chondrites (H, L, LL) result from the heterogeneous physical distribution of a relatively chemically homogeneous metal component among OC parent bodies, and not from a chemical (sensu lato) gradient between H and LL chondrites. |
2021
|
Florin, G., Luais, B., Alard, O., Rushmer, T. Condensation and evaporation processes during CB chondrite formation : Insights from Ge isotopes and highly siderophile element abundances (Article de journal) Dans: Meteoritics & Planetary Science, p. 1–21, 2021. @article{Florin_etal2021,
title = {Condensation and evaporation processes during CB chondrite formation : Insights from Ge isotopes and highly siderophile element abundances},
author = {G. Florin and B. Luais and O. Alard and T. Rushmer},
doi = {10.1111/maps.13698},
year = {2021},
date = {2021-01-01},
journal = {Meteoritics \& Planetary Science},
pages = {1--21},
abstract = {We analyzed the highly siderophile element (HSE) contents and bulk Ge isotopic compositions of large metal grains in the CB chondrites Bencubbin (CBa), Gujba (CBa), and HaH 237 (CBb). Our results suggest that the large grains were formed by the aggregation of smaller condensed grains, and the two Benccubinite groups are distinguishable based on their bulk metal $delta$74/70Ge mass-dependent isotopic values of 0.99 +- 0.30texttenthousand (CBa) and −0.65 +- 0.10texttenthousand (CBb). Based on our observations of these three samples, the isotopic compositions of metal in CBa chondrites are best explained by condensation at slow cooling rates in the center of an impact plume, whereas the metal in CBb chondrites formed under fast cooling rates along the plume edges. We also analyzed the Ge contents and isotopic compositions of the core, intermediate, and rim fractions of two Gujba metal grains, which were separated by sequential digestion. These results show a gradual decrease in $delta$74/70Ge and [Ge] from core to rim. We suggest that these $delta$74Ge zonations result from nearequilibrium condensation and evaporation processes in a heterogeneous plume. We propose a model for their formation in which (1) small grains (to become grain cores) condensed at equilibrium ; (2) these grains were transported to a warmer region of the plume where they reached temperatures lower than that of Fe-Ni condensation, but high enough for the rapid evaporation of Ge ; (3) Ge evaporation followed by slow cooling enriched the grains in heavy Ge isotopes and the surrounding gas in light Ge isotopes ; and (4) equilibrium recondensation of metal from the gas and around the small grains formed the light Ge isotopic zonations observed in grain rims.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We analyzed the highly siderophile element (HSE) contents and bulk Ge isotopic compositions of large metal grains in the CB chondrites Bencubbin (CBa), Gujba (CBa), and HaH 237 (CBb). Our results suggest that the large grains were formed by the aggregation of smaller condensed grains, and the two Benccubinite groups are distinguishable based on their bulk metal $delta$74/70Ge mass-dependent isotopic values of 0.99 +- 0.30texttenthousand (CBa) and −0.65 +- 0.10texttenthousand (CBb). Based on our observations of these three samples, the isotopic compositions of metal in CBa chondrites are best explained by condensation at slow cooling rates in the center of an impact plume, whereas the metal in CBb chondrites formed under fast cooling rates along the plume edges. We also analyzed the Ge contents and isotopic compositions of the core, intermediate, and rim fractions of two Gujba metal grains, which were separated by sequential digestion. These results show a gradual decrease in $delta$74/70Ge and [Ge] from core to rim. We suggest that these $delta$74Ge zonations result from nearequilibrium condensation and evaporation processes in a heterogeneous plume. We propose a model for their formation in which (1) small grains (to become grain cores) condensed at equilibrium ; (2) these grains were transported to a warmer region of the plume where they reached temperatures lower than that of Fe-Ni condensation, but high enough for the rapid evaporation of Ge ; (3) Ge evaporation followed by slow cooling enriched the grains in heavy Ge isotopes and the surrounding gas in light Ge isotopes ; and (4) equilibrium recondensation of metal from the gas and around the small grains formed the light Ge isotopic zonations observed in grain rims. |
Kokh, M. A., Luais, B., Truche, L., Boiron, M. C., Peiffert, C., Schumacher, A. Quantitative measurement of rare earth elements in brines: Isolation from the charged matrix versus direct LA-ICP-MS measurements -- A comparative study (Article de journal) Dans: Geostandards and Geoanalytical Research, 2021. @article{Kokh_etal2021,
title = {Quantitative measurement of rare earth elements in brines: Isolation from the charged matrix versus direct LA-ICP-MS measurements -- A comparative study},
author = {M. A. Kokh and B. Luais and L. Truche and M. C. Boiron and C. Peiffert and A. Schumacher},
doi = {10.1111/ggr.12376},
year = {2021},
date = {2021-01-01},
journal = {Geostandards and Geoanalytical Research},
abstract = {The quantification of the rare earth elements (REEs) in natural rocks and fluids is important not only for the sustainable use of geological resources but also for fundamental geological research. Due to significant improvements in experimental, modelling and analytical techniques, it was discovered that the REEs could be efficiently mobilised and transported by hydrothermal fluids. Thus, determining the REEs in fluids, especially in highly saline solutions, is aprerequisite to understand their fate in hydrothermal fluids. An analytical methodology was established to determine the trace quantities of the REEs in aqueous solutions with compositions typical to seawater and brines. The developed protocol was applied for the quantification of REEs in experimental sodium-rich carbonate-bearing hydrothermal solutions. For this purpose, we used two analytical approaches: (a) the REEs were chromatographically isolated from the charged matrix and introduced into a single collector quadrupole ICP-MS and (b) direct determination of the REEs by LA-ICP-MS in experimental solutions loaded into glass capillaries without any additional isolation procedure. Both LA-ICP-MS and solution nebulisation ICP-MS analysis after isolation of the REEs provide identical data in terms of REE concentrations in brines and are consistent within analytical uncertainties. Being an express method, LA-ICP-MS can be recommended for REE quantification in brines. At the same time, isolation of the REEs from the charged matrix with subsequent ICP-MS measurement provides higher accuracy and precision, giving additional information for the REEs mass fractions that are below the detection limit of the LA-ICP-MS that was estimated at the textasciitilde 10 ng g-1 level.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The quantification of the rare earth elements (REEs) in natural rocks and fluids is important not only for the sustainable use of geological resources but also for fundamental geological research. Due to significant improvements in experimental, modelling and analytical techniques, it was discovered that the REEs could be efficiently mobilised and transported by hydrothermal fluids. Thus, determining the REEs in fluids, especially in highly saline solutions, is aprerequisite to understand their fate in hydrothermal fluids. An analytical methodology was established to determine the trace quantities of the REEs in aqueous solutions with compositions typical to seawater and brines. The developed protocol was applied for the quantification of REEs in experimental sodium-rich carbonate-bearing hydrothermal solutions. For this purpose, we used two analytical approaches: (a) the REEs were chromatographically isolated from the charged matrix and introduced into a single collector quadrupole ICP-MS and (b) direct determination of the REEs by LA-ICP-MS in experimental solutions loaded into glass capillaries without any additional isolation procedure. Both LA-ICP-MS and solution nebulisation ICP-MS analysis after isolation of the REEs provide identical data in terms of REE concentrations in brines and are consistent within analytical uncertainties. Being an express method, LA-ICP-MS can be recommended for REE quantification in brines. At the same time, isolation of the REEs from the charged matrix with subsequent ICP-MS measurement provides higher accuracy and precision, giving additional information for the REEs mass fractions that are below the detection limit of the LA-ICP-MS that was estimated at the textasciitilde 10 ng g-1 level. |
Pasava, J., Ackerman, L., Zak, J., Veselovsky, F., Creaser, R. A., Svojtka, M., Luais, B., Pour, O., Sebek, O., Trubac, J., Vosahlova, E., Cividini, D. Elemental and isotopic compositions of trench-slope black shales, Bohemian Massif, with implications for oceanic and atmospheric oxygenation in early Cambrian (Article de journal) Dans: Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 564, p. 110195, 2021. @article{Pasava_etal2021,
title = {Elemental and isotopic compositions of trench-slope black shales, Bohemian Massif, with implications for oceanic and atmospheric oxygenation in early Cambrian},
author = {J. Pasava and L. Ackerman and J. Zak and F. Veselovsky and R. A. Creaser and M. Svojtka and B. Luais and O. Pour and O. Sebek and J. Trubac and E. Vosahlova and D. Cividini},
doi = {10.1016/j.palaeo.2020.110195},
year = {2021},
date = {2021-01-01},
journal = {Palaeogeography, Palaeoclimatology, Palaeoecology},
volume = {564},
pages = {110195},
abstract = {This study examines a lower Cambrian pyrite-bearing black shale--graywacke succession in the Czech Republic interpreted as infill of a deep-marine, extensional trench-slope basin on top of an accretionary wedge that developed during subduction of an oceanic plate beneath the northern margin of Gondwana. The new U--Pb detrital zircon geochronology of the graywacke constrains the maximum age of deposition to 533 +5/−6 Ma, whereas the Re--Os dating of pyrite yielded a younger age of 507 textpm 16 Ma. Distribution of major and trace elements and calculated enrichment factors (EF) indicate that this succession was deposited under changing redox conditions over a short time span and that the basin was presumably controlled by tectonic subsidence and varying supply of terrigenous arc-derived material. This depositional setting is reflected by largely variable EFs and $delta$98Mo and $delta$53Cr values. Euxinic conditions detected at the base of the sampled black shale interval are documented by the highest values of EFs of redox-sensitive metals (e.g., Mo, U, V, Ni, Co, As) and also the Corg/P (\>1000) and DOPT (\>0.7) values. Black shales show lower $delta$56Fe values due to the excess of authigenic pyrite-Fe with a mean $delta$56Fe value of −0.02texttenthousand over detrital Fe in graywacke with a mean $delta$56Fe value of +0.25texttenthousand. However, the Fe isotopic signatures of the black shales are not consistent with iron shuttling, mixing of authigenic and detrital sources, or hydrothermal metal enrichment. Instead, they most likely resulted from partial oxidation of pyrite through the syndepositional oxidizing hydrothermal fluids (Si--Ba enrichment), which resulted in precipitation of isotopically heavy Fe-oxyhydroxides. We propose that our maximal recorded $delta$98Mo value (+ 0.98texttenthousand) might represent the best estimate for the ancient local seawater Mo composition at around 533 Ma and argues against deep-ocean oxygenation in the early Cambrian. On the other hand, the Se/Co ratios of synsedimentary pyrite indicate a mean atmosphere O2 value of textasciitilde27%.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study examines a lower Cambrian pyrite-bearing black shale--graywacke succession in the Czech Republic interpreted as infill of a deep-marine, extensional trench-slope basin on top of an accretionary wedge that developed during subduction of an oceanic plate beneath the northern margin of Gondwana. The new U--Pb detrital zircon geochronology of the graywacke constrains the maximum age of deposition to 533 +5/−6 Ma, whereas the Re--Os dating of pyrite yielded a younger age of 507 textpm 16 Ma. Distribution of major and trace elements and calculated enrichment factors (EF) indicate that this succession was deposited under changing redox conditions over a short time span and that the basin was presumably controlled by tectonic subsidence and varying supply of terrigenous arc-derived material. This depositional setting is reflected by largely variable EFs and $delta$98Mo and $delta$53Cr values. Euxinic conditions detected at the base of the sampled black shale interval are documented by the highest values of EFs of redox-sensitive metals (e.g., Mo, U, V, Ni, Co, As) and also the Corg/P (>1000) and DOPT (>0.7) values. Black shales show lower $delta$56Fe values due to the excess of authigenic pyrite-Fe with a mean $delta$56Fe value of −0.02texttenthousand over detrital Fe in graywacke with a mean $delta$56Fe value of +0.25texttenthousand. However, the Fe isotopic signatures of the black shales are not consistent with iron shuttling, mixing of authigenic and detrital sources, or hydrothermal metal enrichment. Instead, they most likely resulted from partial oxidation of pyrite through the syndepositional oxidizing hydrothermal fluids (Si--Ba enrichment), which resulted in precipitation of isotopically heavy Fe-oxyhydroxides. We propose that our maximal recorded $delta$98Mo value (+ 0.98texttenthousand) might represent the best estimate for the ancient local seawater Mo composition at around 533 Ma and argues against deep-ocean oxygenation in the early Cambrian. On the other hand, the Se/Co ratios of synsedimentary pyrite indicate a mean atmosphere O2 value of textasciitilde27%. |
Zhu, C., Wen, H., Zhang, Y., Huang, Z., Cloquet, C., Luais, B., Yang, T. Cadmium isotopic constraints on metal sources in the Huize Zn--Pb deposit, SW China (Article de journal) Dans: Geoscience Frontiers, vol. 12, p. 101241, 2021. @article{Zhu_etal2021,
title = {Cadmium isotopic constraints on metal sources in the Huize Zn--Pb deposit, SW China},
author = {C. Zhu and H. Wen and Y. Zhang and Z. Huang and C. Cloquet and B. Luais and T. Yang},
doi = {10.1016/j.gsf.2021.101241},
year = {2021},
date = {2021-01-01},
journal = {Geoscience Frontiers},
volume = {12},
pages = {101241},
abstract = {The Sichuan--Yunnan--Guizhou (SYG) Zn--Pb metallogenic zone in SW China contains \>400 carbonatehosted hydrothermal Zn--Pb deposits. Some of these, such as the Huize, Tianbaoshan, and Daliangzi deposits, are super-large deposits with significant reserves of Cd, Ge, and Ag. However, the sources of these metals remain controversial. This study investigated the Cd isotopic geochemistry of the Huize deposit, the largest Zn--Pb deposit in the SYG area. Sphalerites formed at three stages in the deposit have different colors : black or dark brown (Stage I), red (Stage II), and light-yellow (Stage III). The d114/110Cd values of the sphalerites are in the order Stage III \< Stage I \< Stage II. Kinetic isotopic fractionation is likely the key factor causing the lower d114/110Cd values in the early formed Stage I sphalerites than in laterformed Stage II sphalerites, with cooling of ore-forming fluids being responsible for the still lower values of the Stage III sphalerites. In galena, the d114/110Cd values are inversely correlated with Cd contents and tend to be higher in high-Zn galena. We speculate that Cd isotopic fractionation was significant during the precipitation of sphalerite and galena, with light Cd isotopes being enriched in galena rather than sphalerite. Comparison of the Cd isotopic signatures and Zn/Cd ratios of different endmembers suggests that the d114/110Cd values and Zn/Cd ratios of sphalerite from the Huize deposit, as well as other largescale deposits from the SYG area, are lie in those range of Emeishan basalts and sedimentary rocks and the mean d114/110Cd values of these deposits show good negative correlation with 1/Cd, suggesting that the ore-forming materials of these deposits were derived from the mixing of Emeishan basalts and sedimentary rocks. This study demonstrates that Cd isotopes can be useful proxies in elucidating ore genesis in large Zn--Pb deposits.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Sichuan--Yunnan--Guizhou (SYG) Zn--Pb metallogenic zone in SW China contains >400 carbonatehosted hydrothermal Zn--Pb deposits. Some of these, such as the Huize, Tianbaoshan, and Daliangzi deposits, are super-large deposits with significant reserves of Cd, Ge, and Ag. However, the sources of these metals remain controversial. This study investigated the Cd isotopic geochemistry of the Huize deposit, the largest Zn--Pb deposit in the SYG area. Sphalerites formed at three stages in the deposit have different colors : black or dark brown (Stage I), red (Stage II), and light-yellow (Stage III). The d114/110Cd values of the sphalerites are in the order Stage III < Stage I < Stage II. Kinetic isotopic fractionation is likely the key factor causing the lower d114/110Cd values in the early formed Stage I sphalerites than in laterformed Stage II sphalerites, with cooling of ore-forming fluids being responsible for the still lower values of the Stage III sphalerites. In galena, the d114/110Cd values are inversely correlated with Cd contents and tend to be higher in high-Zn galena. We speculate that Cd isotopic fractionation was significant during the precipitation of sphalerite and galena, with light Cd isotopes being enriched in galena rather than sphalerite. Comparison of the Cd isotopic signatures and Zn/Cd ratios of different endmembers suggests that the d114/110Cd values and Zn/Cd ratios of sphalerite from the Huize deposit, as well as other largescale deposits from the SYG area, are lie in those range of Emeishan basalts and sedimentary rocks and the mean d114/110Cd values of these deposits show good negative correlation with 1/Cd, suggesting that the ore-forming materials of these deposits were derived from the mixing of Emeishan basalts and sedimentary rocks. This study demonstrates that Cd isotopes can be useful proxies in elucidating ore genesis in large Zn--Pb deposits. |
2020
|
Chernonozhkin, S. M., Mercadier, J., Reisberg, L., Luais, B., Zimmermann, C., Morlot, C., Salsi, L., Lecomte, A., Rouer, O., Brouand, M., Doney, A., Ledru, P. Evaluation of rammelsbergite (NiAs2) as a novel mineral for 187Re-187Os dating and implications for unconformity-related U deposits (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 280, p. 85–101, 2020. @article{Chernonozhkin_etal2020,
title = {Evaluation of rammelsbergite (NiAs2) as a novel mineral for 187Re-187Os dating and implications for unconformity-related U deposits},
author = {S. M. Chernonozhkin and J. Mercadier and L. Reisberg and B. Luais and C. Zimmermann and C. Morlot and L. Salsi and A. Lecomte and O. Rouer and M. Brouand and A. Doney and P. Ledru},
doi = {10.1016/j.gca.2020.04.011},
year = {2020},
date = {2020-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {280},
pages = {85--101},
abstract = {Rammelsbergite (NiAs2) is often present in ore deposits worldwide in association with other arsenides, sulphides and sulfarsenides. This work demonstrates the value of the application of the Re-Os isotopic system to the dating of rammelsbergite. Using the example of the Cigar Lake uranium deposit (Athabasca Basin, Saskatchewan, Canada), our results show that rammelsbergite concentrates significant and variable amounts of Re when crystallizing, up to 1.6mgg-1, while incorporating minimal common Os. Such characteristics make this mineral an ideal target for Re-Os isotopic dating, by both isochron and model age methods. Remarkable agreement of the Re-Os age of the rammelsbergite with the U-Pb age of the uranium oxide grains found inside one of the massive rammelsbergite veins confirms the applicability of the method. The selected rammelsbergite samples from the Cigar Lake uranium deposit yield a187Re-187Os isochron age of 1239 +33/-20 Ma. These results challenge a long-standing petrogenetic model which postulates contemporaneous U oxide and Ni-Co-arsenide depositionin unconformity-related uranium deposits. The new Re-Os age of rammelsbergite veins indicates that arsenide crystallization postdated the deposition of the primary uranium oxides at 1461--1341 Ma, implying that uranium oxides and nickel arsenides,as well as other sulphides and sulfarsenides, were not precipitated contemporaneously during a single hydrothermal event as previously proposed. The187Re-187Os data suggest that crystallization of rammelsbergite and co-genetic sulphides, arsenides and sulfarsenides was linked to the ca. 1270 Ma Mackenzie magmatic event, marked by the emplacement of mafic dikes throughout the Canadian Shield, including in the area of the Athabasca Basin. This study therefore suggests a new hypothesis for the origin of nickel, cobalt, sulfur and arsenic in unconformity-related U deposits of the Athabasca Basin. More broadly,the successful application of the187Re-187Os rammelsbergite chronometer in this geological context suggests that its application in other ore deposit environments worldwide is likely to provide similar insights. In this respect, the187Re-187Os chronometer applied to rammelsbergite, and potentially to other arsenides and sulfarsenides, represents a valuable complement to molybdenite dating because it can be used in systems that lack molybdenite.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Rammelsbergite (NiAs2) is often present in ore deposits worldwide in association with other arsenides, sulphides and sulfarsenides. This work demonstrates the value of the application of the Re-Os isotopic system to the dating of rammelsbergite. Using the example of the Cigar Lake uranium deposit (Athabasca Basin, Saskatchewan, Canada), our results show that rammelsbergite concentrates significant and variable amounts of Re when crystallizing, up to 1.6mgg-1, while incorporating minimal common Os. Such characteristics make this mineral an ideal target for Re-Os isotopic dating, by both isochron and model age methods. Remarkable agreement of the Re-Os age of the rammelsbergite with the U-Pb age of the uranium oxide grains found inside one of the massive rammelsbergite veins confirms the applicability of the method. The selected rammelsbergite samples from the Cigar Lake uranium deposit yield a187Re-187Os isochron age of 1239 +33/-20 Ma. These results challenge a long-standing petrogenetic model which postulates contemporaneous U oxide and Ni-Co-arsenide depositionin unconformity-related uranium deposits. The new Re-Os age of rammelsbergite veins indicates that arsenide crystallization postdated the deposition of the primary uranium oxides at 1461--1341 Ma, implying that uranium oxides and nickel arsenides,as well as other sulphides and sulfarsenides, were not precipitated contemporaneously during a single hydrothermal event as previously proposed. The187Re-187Os data suggest that crystallization of rammelsbergite and co-genetic sulphides, arsenides and sulfarsenides was linked to the ca. 1270 Ma Mackenzie magmatic event, marked by the emplacement of mafic dikes throughout the Canadian Shield, including in the area of the Athabasca Basin. This study therefore suggests a new hypothesis for the origin of nickel, cobalt, sulfur and arsenic in unconformity-related U deposits of the Athabasca Basin. More broadly,the successful application of the187Re-187Os rammelsbergite chronometer in this geological context suggests that its application in other ore deposit environments worldwide is likely to provide similar insights. In this respect, the187Re-187Os chronometer applied to rammelsbergite, and potentially to other arsenides and sulfarsenides, represents a valuable complement to molybdenite dating because it can be used in systems that lack molybdenite. |
Decraene, M. N., Marin-Carbonne, J., Bouvier, A. S., Villeneuve, J., Bouden, N., Luais, B., Deloule, E. High spatial resolution measurements of iron isotopes in pyrites by SIMS using the new Hyperion‐II Radio‐Frequency Plasma source (Article de journal) Dans: Rapid Communications in Mass Spectrometry, p. e8986, 2020. @article{Decraene_etal2020,
title = {High spatial resolution measurements of iron isotopes in pyrites by SIMS using the new Hyperion‐II Radio‐Frequency Plasma source},
author = {M. N. Decraene and J. Marin-Carbonne and A. S. Bouvier and J. Villeneuve and N. Bouden and B. Luais and E. Deloule},
doi = {10.1002/rcm.8986},
year = {2020},
date = {2020-01-01},
journal = {Rapid Communications in Mass Spectrometry},
pages = {e8986},
abstract = {RationaleIron isotopic signatures in pyrites are considered as a good proxy to reconstruct paleoenvironmental and local redox conditions. However, the investigation of micro‐pyrites less than 20$mu$m in size has been limited by the evaluable analytical techniques. The development of the new brighter radio‐frequency plasma ion source (Hyperion‐II source) enhances the spatial resolution by increasing the beam density 10 times compared with the Duoplasmatron source.MethodsHere we present high spatial resolution measurements of iron isotopes in pyrites using a 3nA‐3$mu$m primary 16O‐ beam on two Cameca IMS 1280‐HR2 ion microprobe instruments equipped with Hyperion sources at CRPG‐IPNT (France) and at SwissSIMS (Switzerland). We tested analytical effects, such as topography and crystal orientation that could induce analytical biases perceptible through variations of the Instrumental Mass Fractionation (IMF).ResultsThe $delta$56Fe reproducibility for the Balmat pyrite standard is textpm0.25texttenthousand (2SD, standard deviation) and the typical individual internal error is textpm0.10texttenthousand (2SE, standard error). The sensitivity on 56Fe+ was 1.2x107cps/nA/ppm or better. Tests on Balmat pyrites revealed that neither the crystal orientation nor channeling effects seem to significantly influence the IMF. Different pyrite standards (Balmat and SpainCR) were used to test the accuracy of the measurements. Indium mounts must be carefully prepared with sample topography \< 2$mu$m, which was checked using an interferometric microscope. Such a topography is negligible for introducing change in the IMF. This new source increases the spatial resolution while maintaining the high precision of analyses and the overall stability of the measurements compared with the previous Duoplasmatron source.ConclusionsWe developed a reliable method to perform accurate and high‐resolution measurements of micrometric pyrites. The investigation of sedimentary micro‐pyrites will improve our understanding of the processes and environmental conditions during pyrite precipitation, including contribution of primary (microbial activities or abiotic reactions) and secondary signatures (diagenesis and/or hydrothermal fluid circulation).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
RationaleIron isotopic signatures in pyrites are considered as a good proxy to reconstruct paleoenvironmental and local redox conditions. However, the investigation of micro‐pyrites less than 20$mu$m in size has been limited by the evaluable analytical techniques. The development of the new brighter radio‐frequency plasma ion source (Hyperion‐II source) enhances the spatial resolution by increasing the beam density 10 times compared with the Duoplasmatron source.MethodsHere we present high spatial resolution measurements of iron isotopes in pyrites using a 3nA‐3$mu$m primary 16O‐ beam on two Cameca IMS 1280‐HR2 ion microprobe instruments equipped with Hyperion sources at CRPG‐IPNT (France) and at SwissSIMS (Switzerland). We tested analytical effects, such as topography and crystal orientation that could induce analytical biases perceptible through variations of the Instrumental Mass Fractionation (IMF).ResultsThe $delta$56Fe reproducibility for the Balmat pyrite standard is textpm0.25texttenthousand (2SD, standard deviation) and the typical individual internal error is textpm0.10texttenthousand (2SE, standard error). The sensitivity on 56Fe+ was 1.2x107cps/nA/ppm or better. Tests on Balmat pyrites revealed that neither the crystal orientation nor channeling effects seem to significantly influence the IMF. Different pyrite standards (Balmat and SpainCR) were used to test the accuracy of the measurements. Indium mounts must be carefully prepared with sample topography < 2$mu$m, which was checked using an interferometric microscope. Such a topography is negligible for introducing change in the IMF. This new source increases the spatial resolution while maintaining the high precision of analyses and the overall stability of the measurements compared with the previous Duoplasmatron source.ConclusionsWe developed a reliable method to perform accurate and high‐resolution measurements of micrometric pyrites. The investigation of sedimentary micro‐pyrites will improve our understanding of the processes and environmental conditions during pyrite precipitation, including contribution of primary (microbial activities or abiotic reactions) and secondary signatures (diagenesis and/or hydrothermal fluid circulation). |
Korh, A. El, Boiron, M. C., Cathelineau, M., Deloule, E., Luais, B. Tracing metallic pre-concentrations in the Limousin ophiolite-derived rocks and Variscan granites (French Massif Central) (Article de journal) Dans: Lithos, p. 356–357, 2020. @article{ElKorh_etal2020,
title = {Tracing metallic pre-concentrations in the Limousin ophiolite-derived rocks and Variscan granites (French Massif Central)},
author = {A. El Korh and M. C. Boiron and M. Cathelineau and E. Deloule and B. Luais},
doi = {10.1016/j.lithos.2019.105345},
year = {2020},
date = {2020-01-01},
journal = {Lithos},
pages = {356--357},
abstract = {The French Massif Central (FMC) is part of the West European Variscan belt. The economic and sub-economic ore deposits fromthe Limousin area are the consequence of intensive fluid-rock interactions related to a lithosphericdelamination process that occurred during the Neo-Variscan Period (320--290Ma). This study focuses on the fingerprints of fluid-rock interactions in the Limousin ophiolite-derived rocks and granitic massifs, in order to trace the source of trace elements transported by fluids involved in the formation of the Variscan ore deposits (including Sn, W, Au and U deposits). A series of compatible and incompatible metallic trace elements (Ag, As, Au, Bi, Li, Co, Cr, Cu, Ga, Ge, Ni, Pb, Sb, Sc, Sn, Ti, V,W) were analysed in a series of basic (metagabbros, basic dykes), ultrabasic (serpentinites) and felsic (granites and gneisses) rocks, as well as in the mineral assemblages, in order to determine their relationships with the Limousin ore deposits. Serpentinites and theirmineral assemblages (serpentine, olivine, amphibole, chlorite and spinel) show high concentrations in compatible transitionmetals (Sc, V, Cr, Co, Ni, Zn, Cu) and low abundances of incompatible metals (Ge, Ga,Mo, Sn, Sb, W). Associated amphibolites (metagabbros and metamorphosed dykes) show high contents of compatible metals, though lower than ultrabasic rocks. Amphibole and, to a lesser extent, titanite, are the mainhosts for metallic trace elements. Abundances in incompatible metals are generally low. Amphibole has low Sn and Sb contents, while higher Sn contents were measured in titanite. In a UHP zoisite-eclogite cropping out close to one of the ophiolite-derived massifs, zoisite, rutile, omphacite and retrograde amphibole showhigh concentrations of incompatible elements (Sn, Sb,W, As, Ga, Ge, Mo and Bi). However, it has been shown that high-temperature and low-temperature hydrothermal alteration that have affected the basic and ultrabasic protolithsis c. 100Ma older than those that were responsible for the formation of ore deposits. For this reason, and as well because of their low Wand Sn abundances, the ultrabasic and basic rocks cannot be considered as source for the LimousinW-Sn ore deposits.In granite and gneisses, the metallic trace elements are mainly hosted by biotite and muscovite. Quartz and feldspars only show minor amounts of Sc, Ga, Ge, Sn and Pb. The micas contain low amounts of Ge, As, Sb, Bi and variable amounts of Sc, Cu and Ga. Besides, micas display significant Sn and W contents. Variations in Sn and W in micas allow tracing the pre-mineralisation concentrations in the granitic massifs: there is a clear geographical correlation between the Sn and W composition of micas and the importance of the W-Sn ore deposits, arguing for a local source of pre-concentrations. Granites from the Vaulry W-Sn ore deposit display the highest W and Sn concentrations, while granites hosting the Au deposits in the southern part of the Limousin (St-Yrieix, Cheni, Lauri\'{e}ras) show the smallest concentrations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The French Massif Central (FMC) is part of the West European Variscan belt. The economic and sub-economic ore deposits fromthe Limousin area are the consequence of intensive fluid-rock interactions related to a lithosphericdelamination process that occurred during the Neo-Variscan Period (320--290Ma). This study focuses on the fingerprints of fluid-rock interactions in the Limousin ophiolite-derived rocks and granitic massifs, in order to trace the source of trace elements transported by fluids involved in the formation of the Variscan ore deposits (including Sn, W, Au and U deposits). A series of compatible and incompatible metallic trace elements (Ag, As, Au, Bi, Li, Co, Cr, Cu, Ga, Ge, Ni, Pb, Sb, Sc, Sn, Ti, V,W) were analysed in a series of basic (metagabbros, basic dykes), ultrabasic (serpentinites) and felsic (granites and gneisses) rocks, as well as in the mineral assemblages, in order to determine their relationships with the Limousin ore deposits. Serpentinites and theirmineral assemblages (serpentine, olivine, amphibole, chlorite and spinel) show high concentrations in compatible transitionmetals (Sc, V, Cr, Co, Ni, Zn, Cu) and low abundances of incompatible metals (Ge, Ga,Mo, Sn, Sb, W). Associated amphibolites (metagabbros and metamorphosed dykes) show high contents of compatible metals, though lower than ultrabasic rocks. Amphibole and, to a lesser extent, titanite, are the mainhosts for metallic trace elements. Abundances in incompatible metals are generally low. Amphibole has low Sn and Sb contents, while higher Sn contents were measured in titanite. In a UHP zoisite-eclogite cropping out close to one of the ophiolite-derived massifs, zoisite, rutile, omphacite and retrograde amphibole showhigh concentrations of incompatible elements (Sn, Sb,W, As, Ga, Ge, Mo and Bi). However, it has been shown that high-temperature and low-temperature hydrothermal alteration that have affected the basic and ultrabasic protolithsis c. 100Ma older than those that were responsible for the formation of ore deposits. For this reason, and as well because of their low Wand Sn abundances, the ultrabasic and basic rocks cannot be considered as source for the LimousinW-Sn ore deposits.In granite and gneisses, the metallic trace elements are mainly hosted by biotite and muscovite. Quartz and feldspars only show minor amounts of Sc, Ga, Ge, Sn and Pb. The micas contain low amounts of Ge, As, Sb, Bi and variable amounts of Sc, Cu and Ga. Besides, micas display significant Sn and W contents. Variations in Sn and W in micas allow tracing the pre-mineralisation concentrations in the granitic massifs: there is a clear geographical correlation between the Sn and W composition of micas and the importance of the W-Sn ore deposits, arguing for a local source of pre-concentrations. Granites from the Vaulry W-Sn ore deposit display the highest W and Sn concentrations, while granites hosting the Au deposits in the southern part of the Limousin (St-Yrieix, Cheni, Lauriéras) show the smallest concentrations. |
Florin, G., Luais, B., Rushmer, T., Alard, O. Influence of redox processes on the germanium isotopic composition of ordinary chondrites (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 269, p. 270–291, 2020. @article{Florin_etal2020,
title = {Influence of redox processes on the germanium isotopic composition of ordinary chondrites},
author = {G. Florin and B. Luais and T. Rushmer and O. Alard},
doi = {10.1016/j.gca.2019.10.038},
year = {2020},
date = {2020-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {269},
pages = {270--291},
abstract = {Ordinary chondrites (OCs) are classified into three groups, according to their oxidation state, which increases from the H to L to LL groups. This is demonstrated by the decrease in metal content (H = 8 vol},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ordinary chondrites (OCs) are classified into three groups, according to their oxidation state, which increases from the H to L to LL groups. This is demonstrated by the decrease in metal content (H = 8 vol |
2019
|
Belissont, R., Munoz, M., Boiron, M. C., Luais, B., Mathon, O. Germanium crystal chemistry in Cu-bearing sulfides from micro-XRF mapping and micro-XANES spectroscopy (Article de journal) Dans: Minerals, vol. 9, no. 4, p. 227, 2019. @article{Belissont_etal2019,
title = {Germanium crystal chemistry in Cu-bearing sulfides from micro-XRF mapping and micro-XANES spectroscopy},
author = {R. Belissont and M. Munoz and M. C. Boiron and B. Luais and O. Mathon},
doi = {10.3390/min9040227},
year = {2019},
date = {2019-01-01},
journal = {Minerals},
volume = {9},
number = {4},
pages = {227},
abstract = {Germanium is considered a critical element, with a demand that has sharply increased due to booming high-technology industries. To understand Ge incorporation mechanisms in natural systems, we investigate Ge speciation in Cu-bearing sulfide minerals using synchrotron X-ray fluorescence (XRF) chemical mapping and Ge K-edge textmu-X-ray absorption near-edge structures (textmu-XANES) spectroscopy. The samples investigated include (i) a homogeneous chalcopyrite from the Kipushi polymetallic deposit (Central African copperbelt, D.R. Congo) and (ii) a zoned Ge-rich chalcopyrite from the Barrig~ao Cu deposit (Iberian pyrite belt, Portugal). First, our spectroscopic analysis supports the occurrence of tetrahedrally-coordinated Ge4+ in chalcopyrite, independently from origins or zoning patterns observed for these minerals. Then, based on statistical analyses of XRF chemical maps, we demonstrate that tetravalent germanium most likely incorporates chalcopyrite through the Fe crystallographic site via coupled substitutions with the following form : (2x + 3y)Fe3+\<-\>(x + 2y)(Ge,Sn)4+ + x(Zn,Pb)2+ + y(Cu,Ag)+, although the presence of lattice vacancies cannot be completely excluded.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Germanium is considered a critical element, with a demand that has sharply increased due to booming high-technology industries. To understand Ge incorporation mechanisms in natural systems, we investigate Ge speciation in Cu-bearing sulfide minerals using synchrotron X-ray fluorescence (XRF) chemical mapping and Ge K-edge textmu-X-ray absorption near-edge structures (textmu-XANES) spectroscopy. The samples investigated include (i) a homogeneous chalcopyrite from the Kipushi polymetallic deposit (Central African copperbelt, D.R. Congo) and (ii) a zoned Ge-rich chalcopyrite from the Barrig~ao Cu deposit (Iberian pyrite belt, Portugal). First, our spectroscopic analysis supports the occurrence of tetrahedrally-coordinated Ge4+ in chalcopyrite, independently from origins or zoning patterns observed for these minerals. Then, based on statistical analyses of XRF chemical maps, we demonstrate that tetravalent germanium most likely incorporates chalcopyrite through the Fe crystallographic site via coupled substitutions with the following form : (2x + 3y)Fe3+<->(x + 2y)(Ge,Sn)4+ + x(Zn,Pb)2+ + y(Cu,Ag)+, although the presence of lattice vacancies cannot be completely excluded. |
Korh, A. El, Deloule, E., Luais, B., Boiron, M. C., Bastian, L., Vigier, N. Lithium behaviour and isotope fractionation during fluid-rock interactions in Variscan oceanic suture zones : Limousin ophiolite and Ile de Groix high-pressure terrane (France) (Article de journal) Dans: Journal of Petrology, vol. 60, no. 10, p. 1963–1990, 2019. @article{ElKorh_etal2019,
title = {Lithium behaviour and isotope fractionation during fluid-rock interactions in Variscan oceanic suture zones : Limousin ophiolite and Ile de Groix high-pressure terrane (France)},
author = {A. El Korh and E. Deloule and B. Luais and M. C. Boiron and L. Bastian and N. Vigier},
doi = {10.1093/petrology/egz060},
year = {2019},
date = {2019-01-01},
journal = {Journal of Petrology},
volume = {60},
number = {10},
pages = {1963--1990},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2018
|
Greaney, A. T., Rudnick, R. L., Gaschnig, R. M., Whalen, J. B., Luais, B., Clemens, J. D. Geochemistry of molybdenum in the continental crust (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 238, p. 36–54, 2018. @article{Greaney_etal2018,
title = {Geochemistry of molybdenum in the continental crust},
author = {A. T. Greaney and R. L. Rudnick and R. M. Gaschnig and J. B. Whalen and B. Luais and J. D. Clemens},
doi = {10.1016/j.gca.2018.06.039},
year = {2018},
date = {2018-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {238},
pages = {36--54},
abstract = {The use of molybdenum as a quantitative paleo-atmosphere redox sensor is predicated on the assumption that Mo is hosted in sulfides in the upper continental crust (UCC). This assumption is tested here by determining the mineralogical hosts of Mo in typical Archean, Proterozoic, and Phanerozoic upper crustal igneous rocks, spanning a compositional range from basalt to granite. Common igneous sulfides such as pyrite and chalcopyrite contain very little Mo (commonly below detection limits of around 10 ng/g) and are not a significant crustal Mo host. By contrast, volcanic glass and Ti-bearing phases such as titanite, ilmenite, magnetite, and rutile contain significantly higher Mo concentrations (e.g., up to 40 $mu$g/g in titanite), and can account for the whole-rock Mo budget in most rocks. However, mass balance between whole-rock and mineral data is not achieved in 4 out of 10 granites analyzed with in-situ methods, where Mo may be hosted in undetected trace molybdenite. Significant Mo depletion (i.e., UCC-normalized Mo/Ce \< 1) occurs in nearly every granitic rock analyzed here, but not in oceanic basalts or their differentiates (Greaney et al., 2017 ; Jenner and OtextquoterightNeill, 2012). On average, granites are missing 60% of their expected Mo contents. There are two possible reasons for this : (1) Mo partitions into an aqueous magmatic vapor/fluid phase that is expelled from cooling plutons, and/or (2) Mo is partitioned into titaniferous phases during partial melting and fractional crystallization of an evolving magma. The first scenario is likely given the high solubility of oxidized Mo. However, correlations between Mo/Ce and Nb/La in several plutonic suites suggest fractionating phases such as rutile or Fe-Ti oxides may sequester Mo in lower crustal rocks or in subducting slabs in arc settings.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The use of molybdenum as a quantitative paleo-atmosphere redox sensor is predicated on the assumption that Mo is hosted in sulfides in the upper continental crust (UCC). This assumption is tested here by determining the mineralogical hosts of Mo in typical Archean, Proterozoic, and Phanerozoic upper crustal igneous rocks, spanning a compositional range from basalt to granite. Common igneous sulfides such as pyrite and chalcopyrite contain very little Mo (commonly below detection limits of around 10 ng/g) and are not a significant crustal Mo host. By contrast, volcanic glass and Ti-bearing phases such as titanite, ilmenite, magnetite, and rutile contain significantly higher Mo concentrations (e.g., up to 40 $mu$g/g in titanite), and can account for the whole-rock Mo budget in most rocks. However, mass balance between whole-rock and mineral data is not achieved in 4 out of 10 granites analyzed with in-situ methods, where Mo may be hosted in undetected trace molybdenite. Significant Mo depletion (i.e., UCC-normalized Mo/Ce < 1) occurs in nearly every granitic rock analyzed here, but not in oceanic basalts or their differentiates (Greaney et al., 2017 ; Jenner and OtextquoterightNeill, 2012). On average, granites are missing 60% of their expected Mo contents. There are two possible reasons for this : (1) Mo partitions into an aqueous magmatic vapor/fluid phase that is expelled from cooling plutons, and/or (2) Mo is partitioned into titaniferous phases during partial melting and fractional crystallization of an evolving magma. The first scenario is likely given the high solubility of oxidized Mo. However, correlations between Mo/Ce and Nb/La in several plutonic suites suggest fractionating phases such as rutile or Fe-Ti oxides may sequester Mo in lower crustal rocks or in subducting slabs in arc settings. |
2017
|
Korh, A. El, Luais, B., Boiron, M. C., Deloule, E., Cividini, D. Investigation of Ge and Ga exchange behaviour and Ge isotopic fractionation during subduction zone metamorphism (Article de journal) Dans: Chemical Geology, vol. 449, p. 165–181, 2017. @article{ElKorh_etal2017,
title = {Investigation of Ge and Ga exchange behaviour and Ge isotopic fractionation during subduction zone metamorphism},
author = {A. El Korh and B. Luais and M. C. Boiron and E. Deloule and D. Cividini},
doi = {10.1016/j.chemgeo.2016.11.017},
year = {2017},
date = {2017-01-01},
journal = {Chemical Geology},
volume = {449},
pages = {165--181},
abstract = {Germanium(Ge) and gallium(Ga) are slightly to moderately incompatible trace elements during magmatic processes and may be indicators of the nature of the mantle source. Because of their solubility in fluids, Ge and Ga are also geochemical tracers of various hydrothermal processes. Understanding high-pressure/low-temperature (HP--LT) recycling processes of Ge and Ga through fluid-mediated mass transfers in subduction zones can then allow discussing whether they can be source of geochemical heterogeneities in the mantle wedge. We have analysed Ge and Ga abundances and Ge isotope composition of a series of well-characterised HP--LT metabasites of mid-ocean ridge basalt (MORB) affinity and pelitic micaschists fromthe Ile de Groix (France), to determine Ge and Ga behaviour and Ge isotope fractionation during subduction zone metamorphism(SZM). Metabasites have Ge and Ga contents of 1.2--2.1 ppm and 17--22 ppm, respectively, typical of tholeiitic basalts. Garnet-bearing blueschists and eclogites have $delta$74Ge values (+0.42 to +0.65texttenthousand) similar within error to that of tholeiitic basalts (+0.55 to +0.57texttenthousand ; Luais, 2012). Our study shows that during the prograde metamorphism, Ge and Ga abundances and $delta$74Ge values do not vary from blueschists to eclogites, owing to the large stability field of Ge- and Ga-hosting minerals (epidote, garnet, titanite, amphiboles and omphacite) under varying P--T conditions. During the retrograde metamorphism, the slight decrease of the Ga content of c. 8% in greenschists (19 textpm 1 ppm ; 2$sigma$) compared to HP rocks (21 textpm 1 ppm ; 2$sigma$) suggests Ga loss during retrogression, whereas Ge abundances remain within the same range as blueschists and eclogites. In the garnet-bearing greenschists (early stages of retrogression), the $delta$74Ge values (+0.38 to +0.49texttenthousand) remain similar within error to HP rocks. However, albite- and calcite-bearing greenschists have higher $delta$74Ge values (+0.84 to +0.98texttenthousand), showing evidence of Ge fractionation under intensive fluidrock interactions (late stage of retrogression). Micaschists have Ge and Ga abundances within the same range as continental crust and schists. Their variations in $delta$74Ge (+0.29 to+0.70texttenthousand) reflect variations in the sedimentary source and protolith composition. The relatively small variation of $delta$74Ge values inmetabasites compared tomantle rocks implies that the subducted oceanic crust cannot trigger Ge isotopic heterogeneities in the mantle through fluid-induced metasomatism or recycling in the deep mantle. However, during the late stages of retrogression, migration of oxidising fluids along the crust-mantle wedge may be responsible for a resolvable increase of the $delta$74Ge value of the mantle wedge along the subduction channel. Besides, the larger range of Ge concentrations and $delta$74Ge values in the micaschists suggests that recycling of subducted sediments may generate mantle Ge elemental and isotopic heterogeneities.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Germanium(Ge) and gallium(Ga) are slightly to moderately incompatible trace elements during magmatic processes and may be indicators of the nature of the mantle source. Because of their solubility in fluids, Ge and Ga are also geochemical tracers of various hydrothermal processes. Understanding high-pressure/low-temperature (HP--LT) recycling processes of Ge and Ga through fluid-mediated mass transfers in subduction zones can then allow discussing whether they can be source of geochemical heterogeneities in the mantle wedge. We have analysed Ge and Ga abundances and Ge isotope composition of a series of well-characterised HP--LT metabasites of mid-ocean ridge basalt (MORB) affinity and pelitic micaschists fromthe Ile de Groix (France), to determine Ge and Ga behaviour and Ge isotope fractionation during subduction zone metamorphism(SZM). Metabasites have Ge and Ga contents of 1.2--2.1 ppm and 17--22 ppm, respectively, typical of tholeiitic basalts. Garnet-bearing blueschists and eclogites have $delta$74Ge values (+0.42 to +0.65texttenthousand) similar within error to that of tholeiitic basalts (+0.55 to +0.57texttenthousand ; Luais, 2012). Our study shows that during the prograde metamorphism, Ge and Ga abundances and $delta$74Ge values do not vary from blueschists to eclogites, owing to the large stability field of Ge- and Ga-hosting minerals (epidote, garnet, titanite, amphiboles and omphacite) under varying P--T conditions. During the retrograde metamorphism, the slight decrease of the Ga content of c. 8% in greenschists (19 textpm 1 ppm ; 2$sigma$) compared to HP rocks (21 textpm 1 ppm ; 2$sigma$) suggests Ga loss during retrogression, whereas Ge abundances remain within the same range as blueschists and eclogites. In the garnet-bearing greenschists (early stages of retrogression), the $delta$74Ge values (+0.38 to +0.49texttenthousand) remain similar within error to HP rocks. However, albite- and calcite-bearing greenschists have higher $delta$74Ge values (+0.84 to +0.98texttenthousand), showing evidence of Ge fractionation under intensive fluidrock interactions (late stage of retrogression). Micaschists have Ge and Ga abundances within the same range as continental crust and schists. Their variations in $delta$74Ge (+0.29 to+0.70texttenthousand) reflect variations in the sedimentary source and protolith composition. The relatively small variation of $delta$74Ge values inmetabasites compared tomantle rocks implies that the subducted oceanic crust cannot trigger Ge isotopic heterogeneities in the mantle through fluid-induced metasomatism or recycling in the deep mantle. However, during the late stages of retrogression, migration of oxidising fluids along the crust-mantle wedge may be responsible for a resolvable increase of the $delta$74Ge value of the mantle wedge along the subduction channel. Besides, the larger range of Ge concentrations and $delta$74Ge values in the micaschists suggests that recycling of subducted sediments may generate mantle Ge elemental and isotopic heterogeneities. |
Korh, A. El, Luais, B., Deloule, E., Cividini, D. Iron isotope fractionation in subduction‑related high‑pressure metabasites (Ile de Groix, France) (Article de journal) Dans: Contributions to Mineralogy and Petrology, vol. 172, p. 41, 2017. @article{ElKorh_etal2017_2,
title = {Iron isotope fractionation in subduction‑related high‑pressure metabasites (Ile de Groix, France)},
author = {A. El Korh and B. Luais and E. Deloule and D. Cividini},
doi = {10.1007/s00410-017-1357-x},
year = {2017},
date = {2017-01-01},
journal = {Contributions to Mineralogy and Petrology},
volume = {172},
pages = {41},
abstract = {Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes weremeasured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have $delta$56Fe values of +0.16 to +0.33texttenthousand, which are heavier than typical values of MORB and OIB, indicating that theirbasaltic protolith derives from a heavy-Fe mantle source. The $delta$56Fe correlates well with Y/Nb and (La/Sm)PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of $delta$56Fe by +0.06 to 0.10texttenthousand compared to basalts may reflect hydrothermal alteration prior to subduction. The $delta$56Fe decrease from blueschists(+0.19 textpm 0.03 to +0.33 textpm 0.01texttenthousand) to eclogites (+0.16 textpm 0.02 to +0.18 textpm 0.03texttenthousand) reflects small variations in the protolith composition, rather than Fe fractionation during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have $delta$56Fe values (+0.17 textpm 0.01 to+0.27 textpm 0.02texttenthousand) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes weremeasured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have $delta$56Fe values of +0.16 to +0.33texttenthousand, which are heavier than typical values of MORB and OIB, indicating that theirbasaltic protolith derives from a heavy-Fe mantle source. The $delta$56Fe correlates well with Y/Nb and (La/Sm)PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of $delta$56Fe by +0.06 to 0.10texttenthousand compared to basalts may reflect hydrothermal alteration prior to subduction. The $delta$56Fe decrease from blueschists(+0.19 textpm 0.03 to +0.33 textpm 0.01texttenthousand) to eclogites (+0.16 textpm 0.02 to +0.18 textpm 0.03texttenthousand) reflects small variations in the protolith composition, rather than Fe fractionation during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have $delta$56Fe values (+0.17 textpm 0.01 to+0.27 textpm 0.02texttenthousand) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities. |
Rouxel, O., Luais, B. Germanium isotope geochemistry (Article de journal) Dans: Reviews in Mineralogy and Geochemistry, vol. 82, p. 601–656, 2017. @article{Rouxel+Luais2017,
title = {Germanium isotope geochemistry},
author = {O. Rouxel and B. Luais},
doi = {10.2138/rmg.2017.82.14},
year = {2017},
date = {2017-01-01},
journal = {Reviews in Mineralogy and Geochemistry},
volume = {82},
pages = {601--656},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2016
|
Belissont, R., Munoz, M., Boiron, M. C., Luais, B., Mathon, O. Distribution and oxidation state of Ge, Cu and Fe in sphalerite by l-XRF and K-edge l-XANES: insights into Ge incorporation, partitioning and isotopic fractionation (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 177, p. 298–314, 2016. @article{Belissont_etal2016,
title = {Distribution and oxidation state of Ge, Cu and Fe in sphalerite by l-XRF and K-edge l-XANES: insights into Ge incorporation, partitioning and isotopic fractionation},
author = {R. Belissont and M. Munoz and M. C. Boiron and B. Luais and O. Mathon},
doi = {10.1016/j.gca.2016.01.001},
year = {2016},
date = {2016-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {177},
pages = {298--314},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Fritz, J., Tagle, R., Ashworth, L., Schmitt, R. T., Hofmann, A., Luais, B., Harris, P. D., Hoehnel, D., Ozdemir, S., Mohr-Westheide, T., Koeberl, C. Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land, South Africa (Article de journal) Dans: Meteoritics & Planetary Science, vol. 51, no. 12, p. 2441–2458, 2016. @article{Fritz_etal2016,
title = {Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land, South Africa},
author = {J. Fritz and R. Tagle and L. Ashworth and R. T. Schmitt and A. Hofmann and B. Luais and P. D. Harris and D. Hoehnel and S. Ozdemir and T. Mohr-Westheide and C. Koeberl},
doi = {10.1111/maps.12736},
year = {2016},
date = {2016-01-01},
journal = {Meteoritics \& Planetary Science},
volume = {51},
number = {12},
pages = {2441--2458},
abstract = {Abstract--A Paleoarchean impact spherule-bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro-X-ray fluorescence (lXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer-scale, assisted in the localization and characterization of eight spherule-bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The lXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni-Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3-rich and can be distinguished from the Al2O3-poor marine sediments by distinct Al-OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al-OH-rich spherule layers in Al2O3- poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract--A Paleoarchean impact spherule-bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro-X-ray fluorescence (lXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer-scale, assisted in the localization and characterization of eight spherule-bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The lXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni-Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3-rich and can be distinguished from the Al2O3-poor marine sediments by distinct Al-OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al-OH-rich spherule layers in Al2O3- poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism. |
2014
|
Belissont, R., Boiron, M. C., Luais, B., Cathelineau, M. LA-ICP-MS analyses of minor and trace elements and bulk Ge isotopes in zoned Ge-rich sphalerites from the Noailhac -- Saint-Salvy deposit (France): Insights into incorporation mechanisms and ore deposition processes (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 126, p. 518–540, 2014. @article{Belissont_etal2014,
title = {LA-ICP-MS analyses of minor and trace elements and bulk Ge isotopes in zoned Ge-rich sphalerites from the Noailhac -- Saint-Salvy deposit (France): Insights into incorporation mechanisms and ore deposition processes},
author = {R. Belissont and M. C. Boiron and B. Luais and M. Cathelineau},
doi = {10.1016/j.gca.2013.10.052},
year = {2014},
date = {2014-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {126},
pages = {518--540},
abstract = {The increasing worldwide demand in germanium (Ge) is driving renewed research for understanding its geological cycle and the factors controlling its concentration in minerals. The advent of accurate, high-resolution trace element analysis byLA-ICP-MS, as well as the advances in MC-ICP-MS technique for Ge isotopes in sulphides, has enhanced studies in this field. Ge isobaric interferences, standard calibration and data interpretation remain outstanding issues needing to be addressed for more precise and comprehensive LA-ICP-MS analyses.An integrated mineralogical and geochemical study was carried out on typical sphalerite (ZnS) samples from the main Ge deposit in western Europe: the vein-type Zn--Ge--Ag--(Pb--Cd) deposit of Noailhac -- Saint-Salvy (Tarn, France). In situ coupledmeasurements of trace elements and S isotopes were performed using LA-ICP-MS and SIMS, respectively, together with bulk Ge isotopes by MC-ICP-MS. Principal component analyses revealed element clusters antithetically distributed withindistinct zoning types in sphalerite: sector zonings are enriched in Cu, Ge, Ga, Sb and As, whereas rhythmic bandings (dark brown bands primarily) are enriched in Fe, Cd, In and Sn. This typical distribution points to crystallographic controls ontrace element uptake during sphalerite growth, occurring with concomitant microscale variations in fluid compositions at the fluid--crystal interface. Regardless of the zoning type, in all spots, Cu contents approach the sum of tri- and tetravalent cations (Ge, Ga, In, etc.) so that Cu could provide charge-balance for the entire set of coupled substitution mechanisms responsible for the incorporation of the whole range of trace elements in this sphalerite. Strong binary correlations suggest direct substitutions as Zn2+ M (Fe2+, Cd2+) and coupled substitutions as 2Zn2+ MCu+ + Sb3+, 3Zn2+ MGe4+ + 2Ag+, and 3Zn2+ M In3+ + Sn3+ + h (vacancy) despite no clear evidence for the presence of Sn4+. d74GeNIST3120a in bulk sphalerite varies from 2.07 textpm 0.37\&to +0.91 textpm 0.16\&(2r SD) and positively correlates with bulk Ge content. This indicates considerable Ge isotopic fractionation within sphalerite during low-T hydrothermal deposition andzoning processes, associated with possible microscale open system fluid mixing. The trace element features in sphalerite from Saint-Salvy compared with those of other deposits confirm their use as discriminators among genetic types of ores (e.g., high In contents for magmatic-related deposits, and Ge for low-temperature deposits).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The increasing worldwide demand in germanium (Ge) is driving renewed research for understanding its geological cycle and the factors controlling its concentration in minerals. The advent of accurate, high-resolution trace element analysis byLA-ICP-MS, as well as the advances in MC-ICP-MS technique for Ge isotopes in sulphides, has enhanced studies in this field. Ge isobaric interferences, standard calibration and data interpretation remain outstanding issues needing to be addressed for more precise and comprehensive LA-ICP-MS analyses.An integrated mineralogical and geochemical study was carried out on typical sphalerite (ZnS) samples from the main Ge deposit in western Europe: the vein-type Zn--Ge--Ag--(Pb--Cd) deposit of Noailhac -- Saint-Salvy (Tarn, France). In situ coupledmeasurements of trace elements and S isotopes were performed using LA-ICP-MS and SIMS, respectively, together with bulk Ge isotopes by MC-ICP-MS. Principal component analyses revealed element clusters antithetically distributed withindistinct zoning types in sphalerite: sector zonings are enriched in Cu, Ge, Ga, Sb and As, whereas rhythmic bandings (dark brown bands primarily) are enriched in Fe, Cd, In and Sn. This typical distribution points to crystallographic controls ontrace element uptake during sphalerite growth, occurring with concomitant microscale variations in fluid compositions at the fluid--crystal interface. Regardless of the zoning type, in all spots, Cu contents approach the sum of tri- and tetravalent cations (Ge, Ga, In, etc.) so that Cu could provide charge-balance for the entire set of coupled substitution mechanisms responsible for the incorporation of the whole range of trace elements in this sphalerite. Strong binary correlations suggest direct substitutions as Zn2+ M (Fe2+, Cd2+) and coupled substitutions as 2Zn2+ MCu+ + Sb3+, 3Zn2+ MGe4+ + 2Ag+, and 3Zn2+ M In3+ + Sn3+ + h (vacancy) despite no clear evidence for the presence of Sn4+. d74GeNIST3120a in bulk sphalerite varies from 2.07 textpm 0.37&to +0.91 textpm 0.16&(2r SD) and positively correlates with bulk Ge content. This indicates considerable Ge isotopic fractionation within sphalerite during low-T hydrothermal deposition andzoning processes, associated with possible microscale open system fluid mixing. The trace element features in sphalerite from Saint-Salvy compared with those of other deposits confirm their use as discriminators among genetic types of ores (e.g., high In contents for magmatic-related deposits, and Ge for low-temperature deposits). |
Liu, P. P., Zhou, M. F., Luais, B., Cividini, D., Rollion-Bard, C. Disequilibrium iron isotopic fractionation during the high-temperature magmatic differentiation of the Baima Fe--Ti oxide-bearing mafic intrusion, SW China (Article de journal) Dans: Earth and Planetary Science Letters, vol. 399, p. 21–29, 2014. @article{Liu_etal2014,
title = {Disequilibrium iron isotopic fractionation during the high-temperature magmatic differentiation of the Baima Fe--Ti oxide-bearing mafic intrusion, SW China},
author = {P. P. Liu and M. F. Zhou and B. Luais and D. Cividini and C. Rollion-Bard},
doi = {10.1016/j.epsl.2014.05.002},
year = {2014},
date = {2014-01-01},
journal = {Earth and Planetary Science Letters},
volume = {399},
pages = {21--29},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2012
|
Escoube, R., Rouxel, O., Luais, B., Ponzevera, E., Donard, O. F. X. An intercomparison study of the germanium isotope composition of geological reference materials (Article de journal) Dans: Geostandards and Geoanalytical Research, vol. 36, no. 2, p. 149–159, 2012. @article{Escoube_etal2012,
title = {An intercomparison study of the germanium isotope composition of geological reference materials},
author = {R. Escoube and O. Rouxel and B. Luais and E. Ponzevera and O. F. X. Donard},
doi = {10.1111/j.1751-908X.2011.00135.x},
year = {2012},
date = {2012-01-01},
journal = {Geostandards and Geoanalytical Research},
volume = {36},
number = {2},
pages = {149--159},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Luais, B. Germanium chemistry and MC-ICPMS isotopic measurements of Fe--Ni, Zn alloys and silicate matrices: Insights into deep Earth processes (Article de journal) Dans: Chemical Geology, vol. 334, p. 295–311, 2012. @article{Luais2012,
title = {Germanium chemistry and MC-ICPMS isotopic measurements of Fe--Ni, Zn alloys and silicate matrices: Insights into deep Earth processes},
author = {B. Luais},
doi = {10.1016/j.chemgeo.2012.10.017},
year = {2012},
date = {2012-01-01},
journal = {Chemical Geology},
volume = {334},
pages = {295--311},
abstract = {Chemical separation and isotopic measurement of germanium using hexapole-collision cell-MC-ICPMS were developed in various Fe--Ni, ZnS and silicates matrices in order to investigate the potentiality of Ge as an isotopic tracer of planetary differentiation and rock-forming processes. Analytical procedures are described forthe critical step of silicate dissolution in HF+HNO3 medium, as well as for Ge chemical purification using a single cationic-exchange resin step for Fe--Ni and ZnS matrices, and two anionic and cationic resin steps for silicate matrices. Germanium isotopic measurements using MC-ICPMS were performed with appropriateAr+H fluxes in the collision cell to eliminate argide interferences on Ge masses. Three methods of mass bias correction, including sample standard bracketing, external Ga mass bias correction using the exponential law, and the empirical textquotelefttextquoteleftregression methodtextquoterighttextquoteright, give similar results and demonstrate the use of Ga as an appropriate element for mass bias correction of Ge. Results are presented as delta values with respect to JMC Ge standard, and NIST3120a Ge standard for comparison. We show a long-term 2SD reproducibility of less than 0.24texttenthousand on the $delta$74Ge.These analytical methods have been applied to Fe-meteorites, sphalerite (ZnS) deposits, and geostandard silicates ranging from ultramafic to basaltic to granitic compositions, and to an iron formation composition.Fe-meteorites and terrestrial silicate samples display small variations of $delta$74GeJMC=+1.77textpm0.22texttenthousand and +0.89textpm0.16texttenthousand (2SD reproducibility), respectively. This contrasts with the large variations seen in low-temperature rocks, such as the ZnS ores ($delta$74GeJMC=−0.37 to −1.69texttenthousand), and banded iron formations (IF-G Isua, $delta$74GeJMC=+1.38texttenthousand). A slight $delta$74GeJMC--NBO/T negative tendency in silicate samples indicates that polymerisation of silicate melt would control the small Ge isotope fractionation among mantle silicates. A comparison of $delta$74Ge values of iron meteorites and Earth silicate mantle opens new perspectives in deepEarth processes. On the basis of theoretical metal-silicate isotopic equilibrium processes, the low $delta$74Ge of silicate Earth cannot reconcile one-stage process of core--mantle segregation. It is proposed that the $delta$74Ge(JMC) value of silicate earth samples of +0.89textpm0.16texttenthousand (or $delta$74Ge(NIST3120a)=+0.53texttenthousand) represents the composition of the accessible Earth modern mantle. The $delta$74Ge of the silicate mantle in equilibrium with the core at time of core formation would be distinct to that of the present mantle in result of distinct thermodynamic parameters,e.g. fO2, pressure, inducing changes in coordination and valence state of Ge in the silicate crystallographic structure. In addition, the light isotopic composition of the Earthtextquoterights mantle could result from reverse diffusive processes induced by an increase in oxidation state at the end of core formation. This would have some implications on core formation modelling and the use of Ge isotopes for tracing the origin of deep mantle plumes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Chemical separation and isotopic measurement of germanium using hexapole-collision cell-MC-ICPMS were developed in various Fe--Ni, ZnS and silicates matrices in order to investigate the potentiality of Ge as an isotopic tracer of planetary differentiation and rock-forming processes. Analytical procedures are described forthe critical step of silicate dissolution in HF+HNO3 medium, as well as for Ge chemical purification using a single cationic-exchange resin step for Fe--Ni and ZnS matrices, and two anionic and cationic resin steps for silicate matrices. Germanium isotopic measurements using MC-ICPMS were performed with appropriateAr+H fluxes in the collision cell to eliminate argide interferences on Ge masses. Three methods of mass bias correction, including sample standard bracketing, external Ga mass bias correction using the exponential law, and the empirical textquotelefttextquoteleftregression methodtextquoterighttextquoteright, give similar results and demonstrate the use of Ga as an appropriate element for mass bias correction of Ge. Results are presented as delta values with respect to JMC Ge standard, and NIST3120a Ge standard for comparison. We show a long-term 2SD reproducibility of less than 0.24texttenthousand on the $delta$74Ge.These analytical methods have been applied to Fe-meteorites, sphalerite (ZnS) deposits, and geostandard silicates ranging from ultramafic to basaltic to granitic compositions, and to an iron formation composition.Fe-meteorites and terrestrial silicate samples display small variations of $delta$74GeJMC=+1.77textpm0.22texttenthousand and +0.89textpm0.16texttenthousand (2SD reproducibility), respectively. This contrasts with the large variations seen in low-temperature rocks, such as the ZnS ores ($delta$74GeJMC=−0.37 to −1.69texttenthousand), and banded iron formations (IF-G Isua, $delta$74GeJMC=+1.38texttenthousand). A slight $delta$74GeJMC--NBO/T negative tendency in silicate samples indicates that polymerisation of silicate melt would control the small Ge isotope fractionation among mantle silicates. A comparison of $delta$74Ge values of iron meteorites and Earth silicate mantle opens new perspectives in deepEarth processes. On the basis of theoretical metal-silicate isotopic equilibrium processes, the low $delta$74Ge of silicate Earth cannot reconcile one-stage process of core--mantle segregation. It is proposed that the $delta$74Ge(JMC) value of silicate earth samples of +0.89textpm0.16texttenthousand (or $delta$74Ge(NIST3120a)=+0.53texttenthousand) represents the composition of the accessible Earth modern mantle. The $delta$74Ge of the silicate mantle in equilibrium with the core at time of core formation would be distinct to that of the present mantle in result of distinct thermodynamic parameters,e.g. fO2, pressure, inducing changes in coordination and valence state of Ge in the silicate crystallographic structure. In addition, the light isotopic composition of the Earthtextquoterights mantle could result from reverse diffusive processes induced by an increase in oxidation state at the end of core formation. This would have some implications on core formation modelling and the use of Ge isotopes for tracing the origin of deep mantle plumes. |
2011
|
Marin-Carbonne, J., Rollion-Bard, C., Luais, B. In-situ measurements of iron isotopes by SIMS: MC-ICP-MS intercalibration and application to a magnetite crystal from the Gunflint chert (Article de journal) Dans: Chemical Geology, vol. 285, p. 50–61, 2011. @article{Marin-Carbonne_etal2011_2,
title = {In-situ measurements of iron isotopes by SIMS: MC-ICP-MS intercalibration and application to a magnetite crystal from the Gunflint chert},
author = {J. Marin-Carbonne and C. Rollion-Bard and B. Luais},
doi = {10.1016/j.chemgeo.2011.02.019},
year = {2011},
date = {2011-01-01},
journal = {Chemical Geology},
volume = {285},
pages = {50--61},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Martin, C., Brunet, F., Duch^ene, S., Luais, B., Deloule, E. REE and Hf distribution between pyrope and NaCl-bearing water at eclogitic-facies conditions (Article de journal) Dans: European Journal of Mineralogy, vol. 23, p. 343–353, 2011. @article{Martin_etal2011,
title = {REE and Hf distribution between pyrope and NaCl-bearing water at eclogitic-facies conditions},
author = {C. Martin and F. Brunet and S. Duch^ene and B. Luais and E. Deloule},
doi = {10.1127/0935-1221/2011/0023-2124},
year = {2011},
date = {2011-01-01},
journal = {European Journal of Mineralogy},
volume = {23},
pages = {343--353},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Pack, A., Vogel, I., Rollion-Bard, C., Luais, B., Palme, H. Silicon in iron meteorite metal (Article de journal) Dans: Meteoritics & Planetary Science, vol. 46, no. 10, p. 1470–1483, 2011. @article{Pack_etal2011,
title = {Silicon in iron meteorite metal},
author = {A. Pack and I. Vogel and C. Rollion-Bard and B. Luais and H. Palme},
doi = {10.1111/j.1945-5100.2011.01239.x},
year = {2011},
date = {2011-01-01},
journal = {Meteoritics \& Planetary Science},
volume = {46},
number = {10},
pages = {1470--1483},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2010
|
Martin, C., Duchene, S., Luais, B., Goncalves, P., Deloule, E., Fournier, C. Behavior of trace elements in relation to Lu-Hf and Sm-Nd geochronometers during metamorphic dehydration-hydration in the HP domain of VAyenrdalsneset, Western Gneiss Region, Norway (Article de journal) Dans: Contributions to Mineralogy and Petrology, vol. 159, no. 4, p. 437–458, 2010. @article{Martin_etal2010,
title = {Behavior of trace elements in relation to Lu-Hf and Sm-Nd geochronometers during metamorphic dehydration-hydration in the HP domain of VAyenrdalsneset, Western Gneiss Region, Norway},
author = {C. Martin and S. Duchene and B. Luais and P. Goncalves and E. Deloule and C. Fournier},
doi = {10.1016/j.gca.2010.04.057},
year = {2010},
date = {2010-01-01},
journal = {Contributions to Mineralogy and Petrology},
volume = {159},
number = {4},
pages = {437--458},
abstract = {The geochemical and isotopic characterization of an eclogite and the associated retrogressive amphibolite at VAyenrdalsneset, WGR, Norwegian Caledonide was undertaken to investigate the mobility of REE and Hf and the behavior of Lu-Hf and Sm-Nd geochronometers during metamorphic dehydration/rehydration. Eclogitic garnets display a distinct core-rim chemical zoning. Thermodynamic modeling indicates that both cores (13-22 kbar, 500-580A degrees C) and rims (\> 16 kbar, 610-660A degrees C) crystallized under eclogite-facies conditions. The core-rim zoning corresponds to the dehydration of the system. This petrographic disequilibrium is associated with Lu-Hf and Sm-Nd disequilibrium, which prevents dating of the eclogitic stages. At the rock scale, the incoming fluid responsible for eclogite-amphibolite retrogression brought in Sm and Nd, leached Lu, and had no influence on Hf. At the grain scale, mass balance shows that Sm and Nd were stored in clinozoisite since the first eclogitic stage, whereas Lu and Hf, which were more thoroughly redistributed among minerals during retrogression, enable the dating of the amphibolitic facies at 378 +/- A 17 Ma.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The geochemical and isotopic characterization of an eclogite and the associated retrogressive amphibolite at VAyenrdalsneset, WGR, Norwegian Caledonide was undertaken to investigate the mobility of REE and Hf and the behavior of Lu-Hf and Sm-Nd geochronometers during metamorphic dehydration/rehydration. Eclogitic garnets display a distinct core-rim chemical zoning. Thermodynamic modeling indicates that both cores (13-22 kbar, 500-580A degrees C) and rims (> 16 kbar, 610-660A degrees C) crystallized under eclogite-facies conditions. The core-rim zoning corresponds to the dehydration of the system. This petrographic disequilibrium is associated with Lu-Hf and Sm-Nd disequilibrium, which prevents dating of the eclogitic stages. At the rock scale, the incoming fluid responsible for eclogite-amphibolite retrogression brought in Sm and Nd, leached Lu, and had no influence on Hf. At the grain scale, mass balance shows that Sm and Nd were stored in clinozoisite since the first eclogitic stage, whereas Lu and Hf, which were more thoroughly redistributed among minerals during retrogression, enable the dating of the amphibolitic facies at 378 +/- A 17 Ma. |
2009
|
Luais, B., de Veslud, C. Le Carlier, Géraud, Y., Gauthier-Lafaye, F. Comparative behavior of Sr, Nd and Hf isotopic systems during fluid-related deformation at middle crust levels (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 73, p. 2961–2977, 2009. @article{Luais_etal2009,
title = {Comparative behavior of Sr, Nd and Hf isotopic systems during fluid-related deformation at middle crust levels},
author = {B. Luais and C. Le Carlier de Veslud and Y. G\'{e}raud and F. Gauthier-Lafaye},
doi = {10.1016/j.gca.2008.12.026},
year = {2009},
date = {2009-01-01},
journal = {Geochimica et Cosmochimica Acta},
volume = {73},
pages = {2961--2977},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2007
|
Luais, B. Isotopic fractionation of germanium in iron meteorites: Significance for nebular condensation, core formation and impact processes (Article de journal) Dans: Earth and Planetary Science Letters, vol. 262, no. 1-2, p. 21–36, 2007. @article{Luais2007,
title = {Isotopic fractionation of germanium in iron meteorites: Significance for nebular condensation, core formation and impact processes},
author = {B. Luais},
doi = {10.1016/j.epsl.2007.06.031},
year = {2007},
date = {2007-01-01},
journal = {Earth and Planetary Science Letters},
volume = {262},
number = {1-2},
pages = {21--36},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2006
|
Roskosz, M., Luais, B., Watson, H. C., Toplis, M., Alexander, C., Mysen, B. O. Experimental quantification of the fractionation of Fe isotopes during metal segregation from a silicate melt (Article de journal) Dans: Earth and Planetary Science Letters, vol. 248, no. 3-4, p. 851–867, 2006. @article{Roskosz_etal2006,
title = {Experimental quantification of the fractionation of Fe isotopes during metal segregation from a silicate melt},
author = {M. Roskosz and B. Luais and H. C. Watson and M. Toplis and C. Alexander and B. O. Mysen},
doi = {10.1016/j.epsl.2006.06.037},
year = {2006},
date = {2006-01-01},
journal = {Earth and Planetary Science Letters},
volume = {248},
number = {3-4},
pages = {851--867},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2005
|
Chazot, G., Charpentier, S., Kornprost, J., Vanucci, R., Luais, B. Lithospheric mantle evolution during continental break-up: the West Iberia non volcanic passive margin (Article de journal) Dans: Journal of Petrology, vol. 46, no. 12, p. 2527–2568, 2005. @article{Chazot_etal2005,
title = {Lithospheric mantle evolution during continental break-up: the West Iberia non volcanic passive margin},
author = {G. Chazot and S. Charpentier and J. Kornprost and R. Vanucci and B. Luais},
doi = {10.1093/petrology/egi064},
year = {2005},
date = {2005-01-01},
journal = {Journal of Petrology},
volume = {46},
number = {12},
pages = {2527--2568},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Meyzen, C., Ludden, J., Humler, E., Luais, B., Toplis, M., Mével, C., Storey, M. New insights into the origin and distribution of the DUPAL isotope anomaly in the Indian Ocean mantle from MORB of the Southwest Indian Ridge (Article de journal) Dans: Geochemistry Geophysics Geosystems G3, vol. 6, no. 11, p. 1–34, 2005. @article{Meyzen_etal2005,
title = {New insights into the origin and distribution of the DUPAL isotope anomaly in the Indian Ocean mantle from MORB of the Southwest Indian Ridge},
author = {C. Meyzen and J. Ludden and E. Humler and B. Luais and M. Toplis and C. M\'{e}vel and M. Storey},
doi = {10.1029/2005GC000979},
year = {2005},
date = {2005-01-01},
journal = {Geochemistry Geophysics Geosystems G3},
volume = {6},
number = {11},
pages = {1--34},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2004
|
Luais, B. Temporal changes in Nd isotopic composition of Piton de la Fournaise magmatism (Réunion Island, Indian Ocean) (Article de journal) Dans: Geochemistry, Geophysics, Geosystems G3, vol. 5, p. Q01008, 2004. @article{Luais2004,
title = {Temporal changes in Nd isotopic composition of Piton de la Fournaise magmatism (R\'{e}union Island, Indian Ocean)},
author = {B. Luais},
doi = {10.1029/2002GC000502},
year = {2004},
date = {2004-01-01},
journal = {Geochemistry, Geophysics, Geosystems G3},
volume = {5},
pages = {Q01008},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2001
|
Sigoyer, J. De, Chavagnac, V., Blichert-Toft, J., Villa, I. M., Luais, B., Guillot, S., Cosca, M., Mascle, G. Dating Indian continental subduction and collisional thickening in NW Himalaya: Multichronometry of the Tso Morari eclogites: Reply (Article de journal) Dans: Geology, vol. 29, no. 2, p. 192, 2001. @article{DeSigoyer_etal2001,
title = {Dating Indian continental subduction and collisional thickening in NW Himalaya: Multichronometry of the Tso Morari eclogites: Reply},
author = {J. De Sigoyer and V. Chavagnac and J. Blichert-Toft and I. M. Villa and B. Luais and S. Guillot and M. Cosca and G. Mascle},
year = {2001},
date = {2001-01-01},
journal = {Geology},
volume = {29},
number = {2},
pages = {192},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Luais, B., Duch^ene, S., Sigoyer, J. De Sm-Nd disequilibrium in high-pressure low Temperature Himalayan and Alpine rocks (Article de journal) Dans: Tectonophysics Special issue textquotelefttextquoteleftExhumation of high-pressure rocks: kinetic, thermal and mechanical constraints textquoterighttextquoteright, vol. 342, no. 1-2, p. 1–22, 2001. @article{Luais_etal2001,
title = {Sm-Nd disequilibrium in high-pressure low Temperature Himalayan and Alpine rocks},
author = {B. Luais and S. Duch^ene and J. De Sigoyer},
year = {2001},
date = {2001-01-01},
journal = {Tectonophysics Special issue textquotelefttextquoteleftExhumation of high-pressure rocks: kinetic, thermal and mechanical constraints textquoterighttextquoteright},
volume = {342},
number = {1-2},
pages = {1--22},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2000
|
Sigoyer, J. De, Chavagnac, V., Blichert-Toft, J., Villa, I. M., Luais, B., Guillot, S., Cosca, M., Mascle, G. Dating Indian continental subduction and collisional thickening in northwest Himalaya : multichronology of the Tso Morari eclogites (Article de journal) Dans: Geology, vol. 28, no. 6, p. 487–490, 2000. @article{DeSigoyer_etal2000,
title = {Dating Indian continental subduction and collisional thickening in northwest Himalaya : multichronology of the Tso Morari eclogites},
author = {J. De Sigoyer and V. Chavagnac and J. Blichert-Toft and I. M. Villa and B. Luais and S. Guillot and M. Cosca and G. Mascle},
doi = {10.1130/0091-7613(2000)28\<487:DTICSA\>2.0.CO;2},
year = {2000},
date = {2000-01-01},
journal = {Geology},
volume = {28},
number = {6},
pages = {487--490},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
0000
|
Rouxel, O., Luais, B. The isotope geochemistry of germanium (Article de journal) Dans: Reviews in Mineralogy and Geochemistry, 0000. @article{Rouxel+Luais,
title = {The isotope geochemistry of germanium},
author = {O. Rouxel and B. Luais},
journal = {Reviews in Mineralogy and Geochemistry},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
