Abstract. The formation of metamorphic zircon after baddeleyite is a well-known reaction that can be used to date the metamorphism of igneous silica-undersaturated rocks. By contrast, metamorphic minerals formed after igneous zirconolite have rarely been reported. In this paper, we document metamorphic titanite + zircon pseudomorphs formed from the metamorphic breakdown of igneous zirconolite in syenodiorite and syenite, in the southeastern Sveconorwegian Province, Sweden. Water-rich fluid influx during tectonometamorphism in epidote–amphibolite-facies metamorphic conditions caused the release of silica during a metamorphic reaction involving igneous feldspar and pyroxene and the simultaneous breakdown of igneous Zr-bearing phases. Typical titanite + zircon intergrowths are elongated or platy titanite crystals speckled with tiny inclusions of zircon. Most intergrowths are smaller than 15 µm; some are subrounded in shape. Locally, bead-like grains of titanite and zircon are intergrown with silicate minerals. The precursor igneous zirconolite was found preserved only in a sample of near-pristine igneous syenodiorite, as remnant grains of mainly < 2 µm in size. Two somewhat larger crystals, 8 and 12 µm, allowed semiquantitative confirmation using microprobe analysis. Analogous with zircon pseudomorphs after baddeleyite, titanite + zircon pseudomorphs after zirconolite potentially offer dating of the metamorphic reaction, although the small size of the crystals makes dating with today's techniques challenging. The scarcity of reports of zirconolite and pseudomorphs reflects that they are either rare or possibly overlooked.
{"title":"Metamorphic titanite–zircon pseudomorphs after igneous zirconolite","authors":"Cindy L. Urueña, Charlotte Möller, Anders Plan","doi":"10.5194/ejm-35-773-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-773-2023","url":null,"abstract":"Abstract. The formation of metamorphic zircon after baddeleyite is a well-known reaction that can be used to date the metamorphism of igneous silica-undersaturated rocks. By contrast, metamorphic minerals formed after igneous zirconolite have rarely been reported. In this paper, we document metamorphic titanite + zircon pseudomorphs formed from the metamorphic breakdown of igneous zirconolite in syenodiorite and syenite, in the southeastern Sveconorwegian Province, Sweden. Water-rich fluid influx during tectonometamorphism in epidote–amphibolite-facies metamorphic conditions caused the release of silica during a metamorphic reaction involving igneous feldspar and pyroxene and the simultaneous breakdown of igneous Zr-bearing phases. Typical titanite + zircon intergrowths are elongated or platy titanite crystals speckled with tiny inclusions of zircon. Most intergrowths are smaller than 15 µm; some are subrounded in shape. Locally, bead-like grains of titanite and zircon are intergrown with silicate minerals. The precursor igneous zirconolite was found preserved only in a sample of near-pristine igneous syenodiorite, as remnant grains of mainly < 2 µm in size. Two somewhat larger crystals, 8 and 12 µm, allowed semiquantitative confirmation using microprobe analysis. Analogous with zircon pseudomorphs after baddeleyite, titanite + zircon pseudomorphs after zirconolite potentially offer dating of the metamorphic reaction, although the small size of the crystals makes dating with today's techniques challenging. The scarcity of reports of zirconolite and pseudomorphs reflects that they are either rare or possibly overlooked.","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135014456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alessandra Altieri, Federico Pezzotta, Giovanni B. Andreozzi, Henrik Skogby, Ferdinando Bosi
Abstract. Tourmaline crystals from the island of Elba commonly display a sharp transition to dark colors at the analogous termination due to the incorporation of Fe and/or Mn during the latest stages of crystallization in pegmatites. The formation of such color anomalies is related to a dramatic physicochemical change in the crystallization environment as a consequence of an opening of the geochemical system. However, mechanisms that may lead to the availability of Fe and/or Mn in the residual cavity fluids have been unclear. On the basis of chemical and spectroscopic investigations, combined with structural and paragenetic observations of the cavities, we propose a general genetic model in which, as a consequence of a pocket rupture event, chemical alteration of Fe- and Mn-rich minerals that formed early in the pegmatitic rock surrounding the cavities occurred through leaching processes, produced by the action of the highly reactive late-stage cavity fluids. Such processes were responsible for the release of Fe and Mn in the geochemical system, allowing the formation of the late-stage dark-colored terminations in the tourmaline crystals. In some cavities, a high availability of Mn and/or Fe determined the evolution of the crystals from an initial elbaite/fluor-elbaite composition to celleriite, foitite or schorl. This compositional evolution trend can be described by the following general chemical substitution: XNa+ + Y(Li1.5 + Al0.5)3+ + WF− ↔ X□ + 2Y(Fe,Mn)2+ + WOH−.
{"title":"Genetic model for the color anomalies at the termination of pegmatitic gem tourmaline crystals from the island of Elba, Italy","authors":"Alessandra Altieri, Federico Pezzotta, Giovanni B. Andreozzi, Henrik Skogby, Ferdinando Bosi","doi":"10.5194/ejm-35-755-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-755-2023","url":null,"abstract":"Abstract. Tourmaline crystals from the island of Elba commonly display a sharp transition to dark colors at the analogous termination due to the incorporation of Fe and/or Mn during the latest stages of crystallization in pegmatites. The formation of such color anomalies is related to a dramatic physicochemical change in the crystallization environment as a consequence of an opening of the geochemical system. However, mechanisms that may lead to the availability of Fe and/or Mn in the residual cavity fluids have been unclear. On the basis of chemical and spectroscopic investigations, combined with structural and paragenetic observations of the cavities, we propose a general genetic model in which, as a consequence of a pocket rupture event, chemical alteration of Fe- and Mn-rich minerals that formed early in the pegmatitic rock surrounding the cavities occurred through leaching processes, produced by the action of the highly reactive late-stage cavity fluids. Such processes were responsible for the release of Fe and Mn in the geochemical system, allowing the formation of the late-stage dark-colored terminations in the tourmaline crystals. In some cavities, a high availability of Mn and/or Fe determined the evolution of the crystals from an initial elbaite/fluor-elbaite composition to celleriite, foitite or schorl. This compositional evolution trend can be described by the following general chemical substitution: XNa+ + Y(Li1.5 + Al0.5)3+ + WF− ↔ X□ + 2Y(Fe,Mn)2+ + WOH−.","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135397079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Berkh, J. Majzlan, J. Meima, Jakub Plášil, D. Rammlmair
Abstract. Enargite (Cu3AsS4) and tennantite (Cu12As4S13) are typical As-bearing sulfides in intermediate- and high-sulfidation epithermal deposits. Trace and major element variations in enargite and tennantite and their substitution mechanisms are widely described. However, Raman spectra of the minerals with correlative quantitative chemical information are rarely documented, especially for enargite. Therefore, comparative electron and μ-Raman microprobe analyses were performed on enargite and fahlore grains. These spectra can be used in the industrial detection and subsequent removal of As-bearing sulfides prior to ore beneficiation in order to diminish the environmental impact of the metallurgical technologies. A simple Sb5+–As5+ substitution in enargite was confirmed by Raman analyses. Similarly, a complete solid solution series from tetrahedrite to tennantite (i.e., Sb3+–As3+ substitution) can be correlated with a gradual evolution in their Raman spectra. In turn, Te4+ occupies the As3+ and Sb3+ sites in fahlore by the coupled substitution Te4+ + Cu+ → (As, Sb)3+ + (Cu, Fe, Zn)2+. Accordingly, Raman bands of goldfieldite (Te-rich member) are strongly broadened compared with those of tetrahedrite and tennantite. A secondary phase with high porosity and a fibrous or wormlike texture was found in enargite in a weathered sample. The chemical composition, Raman spectrum, and X-ray diffraction signature of the secondary phase resemble tennantite. A gradual transformation of the primary enargite into this secondary phase was visualized by comparative electron and Raman microprobe mapping.
{"title":"The effect of chemical variability and weathering on Raman spectra of enargite and fahlore","authors":"K. Berkh, J. Majzlan, J. Meima, Jakub Plášil, D. Rammlmair","doi":"10.5194/ejm-35-737-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-737-2023","url":null,"abstract":"Abstract. Enargite (Cu3AsS4) and tennantite\u0000(Cu12As4S13) are typical As-bearing sulfides in intermediate-\u0000and high-sulfidation epithermal deposits. Trace and major element variations\u0000in enargite and tennantite and their substitution mechanisms are widely\u0000described. However, Raman spectra of the minerals with correlative\u0000quantitative chemical information are rarely documented, especially for\u0000enargite. Therefore, comparative electron and μ-Raman microprobe\u0000analyses were performed on enargite and fahlore grains. These spectra can be\u0000used in the industrial detection and subsequent removal of As-bearing sulfides\u0000prior to ore beneficiation in order to diminish the environmental impact of\u0000the metallurgical technologies. A simple Sb5+–As5+ substitution in enargite was confirmed by Raman\u0000analyses. Similarly, a complete solid solution series from tetrahedrite to\u0000tennantite (i.e., Sb3+–As3+ substitution) can be correlated with a\u0000gradual evolution in their Raman spectra. In turn, Te4+ occupies the\u0000As3+ and Sb3+ sites in fahlore by the coupled substitution\u0000Te4+ + Cu+ → (As, Sb)3+ + (Cu, Fe, Zn)2+.\u0000Accordingly, Raman bands of goldfieldite (Te-rich member) are strongly\u0000broadened compared with those of tetrahedrite and tennantite. A secondary phase with high porosity and a fibrous or wormlike texture was\u0000found in enargite in a weathered sample. The chemical composition, Raman\u0000spectrum, and X-ray diffraction signature of the secondary phase resemble\u0000tennantite. A gradual transformation of the primary enargite into this\u0000secondary phase was visualized by comparative electron and Raman microprobe\u0000mapping.","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48677034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Pristine amphibole–clinozoisite eclogite from within the eclogite type locality (Hohl, Koralpe) of the Eastern Alps in Austria preserves centimetre-thick, concordant, laterally continuous leucocratic segregations of coarse-grained (up to ∼ 1 cm grain diameter) euhedral amphibole–clinozoisite–quartz and disseminated garnet–omphacite–rutile. The segregations locally show selvedges dominated by coarse-grained amphibole at the interface with their host eclogite. Retrogression is limited to thin films of texturally late plagioclase ± amphibole and minor symplectites of diopside–plagioclase partially replacing omphacite. Mineral compositions are largely homogeneous except for clinozoisite, which is significantly enriched in Fe3+, rare-earth and high-field-strength elements in the rock matrix compared to that in segregations. Petrography, mineral chemical data and phase diagram modelling are interpreted in terms of limited melting under high-aH2O conditions, at or close to the well-established pressure maximum (21 ± 3 kbar and 680–740 ∘C), followed by melt crystallization near these conditions. Exsolution of melt-dissolved H2O led to the formation of the amphibole-rich selvedges at the leucosome–eclogite interface. Plagioclase ± amphibole/clinopyroxene films formed at lower pressure from final melt vestiges adhering to grain boundaries or from secondary fluid–rock interaction. Natural variability in rock composition and the bulk oxidation state leads to variable mineral modes and calculated high-pressure solidus temperatures for compositional end-members sampled at Hohl. Modelling suggests that oxidized conditions (XFe3+<0.5) favour hydrated but refractory amphibole–clinozoisite-rich assemblages with a fluid-present solidus temperature of ∼ 740 ∘C at 20 kbar, whereas more reduced conditions (XFe3+∼0.2) yield “true” eclogites (> 80 vol % garnet + omphacite) that commence melting at ∼ 720 ∘C at the same pressure. The interlayering of such eclogites potentially constitutes a fluid source–sink couple under appropriate pressure–temperature conditions, favouring fluid transfer from neighbouring dehydrating layers to melt-bearing ones down gradients in the chemical potential of H2O (μH2O). Phase diagram calculations show that for moderate degrees of fluid-fluxed melting (≤ 10 vol % melt) near the pressure maximum, the observed equilibrium assemblage is preserved, provided the melt is subsequently removed from the source rock. The resulting hydrous melts may be, in part, parents to similar eclogite-hosted pegmatitic segregations described in the eclogite type locality. We suggest that eclogites with a comparable composition and metamorphic history are however unlikely to produce voluminous melts.
{"title":"Partial melting of amphibole–clinozoisite eclogite at the pressure maximum (eclogite type locality, Eastern Alps, Austria)","authors":"S. Schorn, Anna Rogowitz, C. Hauzenberger","doi":"10.5194/ejm-35-715-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-715-2023","url":null,"abstract":"Abstract. Pristine amphibole–clinozoisite eclogite from within the eclogite type locality (Hohl, Koralpe) of the Eastern Alps in Austria preserves centimetre-thick, concordant, laterally continuous leucocratic segregations of coarse-grained (up to ∼ 1 cm grain diameter) euhedral amphibole–clinozoisite–quartz and disseminated garnet–omphacite–rutile. The segregations locally show selvedges dominated by coarse-grained amphibole at the interface with their host eclogite. Retrogression is limited to thin films of texturally late plagioclase ± amphibole and minor symplectites of diopside–plagioclase partially replacing omphacite. Mineral compositions are largely homogeneous except for clinozoisite, which is significantly enriched in Fe3+, rare-earth and high-field-strength elements in the rock matrix compared to that in segregations. Petrography, mineral chemical data and phase diagram modelling are interpreted in terms of limited melting under high-aH2O conditions, at or close to the well-established pressure maximum (21 ± 3 kbar and 680–740 ∘C), followed by melt crystallization near these conditions. Exsolution of melt-dissolved H2O led to the formation of the amphibole-rich selvedges at the leucosome–eclogite interface. Plagioclase ± amphibole/clinopyroxene films formed at lower pressure from final melt vestiges adhering to grain boundaries or from secondary fluid–rock interaction. Natural variability in rock composition and the bulk oxidation state leads to variable mineral modes and calculated high-pressure solidus temperatures for compositional end-members sampled at Hohl. Modelling suggests that oxidized conditions (XFe3+<0.5) favour hydrated but refractory amphibole–clinozoisite-rich assemblages with a fluid-present solidus temperature of ∼ 740 ∘C at 20 kbar, whereas more reduced conditions (XFe3+∼0.2) yield “true” eclogites (> 80 vol % garnet + omphacite) that commence melting at ∼ 720 ∘C at the same pressure. The interlayering of such eclogites potentially constitutes a fluid source–sink couple under appropriate pressure–temperature conditions, favouring fluid transfer from neighbouring dehydrating layers to melt-bearing ones down gradients in the chemical potential of H2O (μH2O). Phase diagram calculations show that for moderate degrees of fluid-fluxed melting (≤ 10 vol % melt) near the pressure maximum, the observed equilibrium assemblage is preserved, provided the melt is subsequently removed from the source rock. The resulting hydrous melts may be, in part, parents to similar eclogite-hosted pegmatitic segregations described in the eclogite type locality. We suggest that eclogites with a comparable composition and metamorphic history are however unlikely to produce voluminous melts.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46925796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Mauro, C. Biagioni, J. Sejkora, Z. Dolníček, R. Škoda
Abstract. The new mineral batoniite, [Al8(OH)14(H2O)18](SO4)5 ⋅ 5H2O, was discovered in the Cetine di Cotorniano Mine, Chiusdino, Siena, Tuscany, Italy. It occurs as hemispherical aggregates composed of brittle tabular crystals, up to 1 mm in size, white to colorless in color, with a white streak and a vitreous to greasy luster. Batoniite is biaxial negative, with α= 1.4833(6), β= 1.4948(6), γ= 1.5019(5) (589 nm), and 2V(meas.)= 71(1)∘. Electron microprobe analysis, affected by the dehydration of batoniite under the chamber vacuum, gave (in wt %) the following: Al2O3 33.48, Fe2O3 0.05, SO3 33.00, and H2Ocalc 44.41, total 110.94. It corresponds to the chemical formula (Al7.98Fe0.013+)Σ7.99(SO4)5.01(OH)13.95(H2O)18 ⋅ 5H2O. Batoniite is triclinic, belonging to space group P1‾, with a= 9.1757(6), b= 12.0886(9), c= 20.9218(15) Å, α= 82.901(3), β= 87.334(3), γ= 86.999(2)∘, V= 2297.8(3) Å3, and Z= 2. The crystal structure was refined to R1= 0.0916 for 8118 unique reflections with Fo>4σ(Fo) and 811 refined parameters and 60 restraints. Batoniite is characterized by isolated [Al8(OH)14(H2O)18]10+ polyoxocations, H-bonded to five interstitial (SO4)2− and five H2O groups. In type material, it is associated with gypsum and a poorly crystallized Al–Fe sulfate. The crystallization of batoniite is probably due to the action of H2SO4 on Al-bearing rocks of Paleozoic age cropping out in the Garibaldi Tunnel, the lowest mining level of the Cetine di Cotorniano Mine.
{"title":"Batoniite, [Al8(OH)14(H2O)18](SO4)5 ⋅ 5H2O, a new mineral with the [Al8(OH)14(H2O)18]10+ polyoxocation from the Cetine di Cotorniano Mine, Tuscany, Italy","authors":"D. Mauro, C. Biagioni, J. Sejkora, Z. Dolníček, R. Škoda","doi":"10.5194/ejm-35-703-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-703-2023","url":null,"abstract":"Abstract. The new mineral batoniite,\u0000[Al8(OH)14(H2O)18](SO4)5 ⋅ 5H2O,\u0000was discovered in the Cetine di Cotorniano Mine, Chiusdino, Siena,\u0000Tuscany, Italy. It occurs as hemispherical aggregates composed of brittle\u0000tabular crystals, up to 1 mm in size, white to colorless in color, with a\u0000white streak and a vitreous to greasy luster. Batoniite is biaxial negative,\u0000with α= 1.4833(6), β= 1.4948(6), γ= 1.5019(5)\u0000(589 nm), and 2V(meas.)= 71(1)∘. Electron microprobe\u0000analysis, affected by the dehydration of batoniite under the chamber vacuum,\u0000gave (in wt %) the following: Al2O3 33.48, Fe2O3 0.05, SO3\u000033.00, and H2Ocalc 44.41, total 110.94. It corresponds to the chemical\u0000formula (Al7.98Fe0.013+)Σ7.99(SO4)5.01(OH)13.95(H2O)18 ⋅ 5H2O. Batoniite is triclinic, belonging to space group P1‾, with a= 9.1757(6), b= 12.0886(9), c= 20.9218(15) Å, α= 82.901(3),\u0000β= 87.334(3), γ= 86.999(2)∘, V= 2297.8(3) Å3, and Z= 2. The crystal structure was refined to R1= 0.0916\u0000for 8118 unique reflections with Fo>4σ(Fo) and\u0000811 refined parameters and 60 restraints. Batoniite is characterized by\u0000isolated [Al8(OH)14(H2O)18]10+ polyoxocations,\u0000H-bonded to five interstitial (SO4)2− and five H2O groups. In\u0000type material, it is associated with gypsum and a poorly crystallized Al–Fe\u0000sulfate. The crystallization of batoniite is probably due to the action of\u0000H2SO4 on Al-bearing rocks of Paleozoic age cropping out in the\u0000Garibaldi Tunnel, the lowest mining level of the Cetine di Cotorniano Mine.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46518585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. The incorporation mechanisms of OH groups in garnet were investigated in a suite of high-pressure rocks from the Zermatt–Saas area (Switzerland) using a combination of Fourier transform infrared spectroscopy (FTIR) and electron probe micro-analysis (EPMA). Investigated garnet specimens include grossular–andradite–uvarovite solid solutions in serpentinite and rodingite and almandine–grossular–pyrope–spessartine solid solutions in eclogite, mafic fels and meta-sediment. All rocks experienced the same peak metamorphic conditions corresponding to a burial depth of ∼ 80 km (∼ 540 ∘C, 2.3 GPa), allowing determination of the OH content in garnet as a function of rock type. The capacity for OH incorporation into garnet strongly depends on its composition. Andradite-rich (400–5000 µg g−1 H2O) and grossular-rich garnet (200–1800 µg g−1 H2O) contain at least 1 order of magnitude more H2O than almandine-rich garnet (< 120 µg g−1 H2O). Microscale analyses using FTIR and EPMA profiles and maps reveal the preservation of OH zoning throughout the metamorphic history of the samples. The OH content correlates strongly with Mn, Ca and Ti zoning and produces distinct absorption bands that are characteristic of multiple nano-scale OH environments. The use of 2D diffusion modelling suggests that H diffusion rates in these rocks is as low as log(D[m2 s−1]) = −24.5 at 540 ∘C. Data were collected for the main garnet-bearing rock types of the Zermatt–Saas area allowing a mass balance model of H2O to be calculated. The result shows that ∼ 3360 kg H2O km−1 (section of oceanic crust) yr−1 could be transported by garnet in the subducting slab beyond 80 km depth and contributed to the deep-Earth water cycle during the Eocene subduction of the Piemonte–Liguria Ocean.
{"title":"OH incorporation and retention in eclogite-facies garnets from the Zermatt–Saas area (Switzerland) and their contribution to the deep water cycle","authors":"J. Reynes, Jörg Hermann, P. Lanari, T. Bovay","doi":"10.5194/ejm-35-679-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-679-2023","url":null,"abstract":"Abstract. The incorporation mechanisms of OH groups in garnet were\u0000investigated in a suite of high-pressure rocks from the Zermatt–Saas area\u0000(Switzerland) using a combination of Fourier transform infrared spectroscopy\u0000(FTIR) and electron probe micro-analysis (EPMA). Investigated garnet\u0000specimens include grossular–andradite–uvarovite solid solutions in\u0000serpentinite and rodingite and almandine–grossular–pyrope–spessartine\u0000solid solutions in eclogite, mafic fels and meta-sediment. All rocks\u0000experienced the same peak metamorphic conditions corresponding to a burial\u0000depth of ∼ 80 km (∼ 540 ∘C, 2.3 GPa),\u0000allowing determination of the OH content in garnet as a function of rock\u0000type. The capacity for OH incorporation into garnet strongly depends on its\u0000composition. Andradite-rich (400–5000 µg g−1 H2O) and\u0000grossular-rich garnet (200–1800 µg g−1 H2O) contain at\u0000least 1 order of magnitude more H2O than almandine-rich garnet\u0000(< 120 µg g−1 H2O). Microscale analyses using FTIR\u0000and EPMA profiles and maps reveal the preservation of OH zoning throughout\u0000the metamorphic history of the samples. The OH content correlates strongly\u0000with Mn, Ca and Ti zoning and produces distinct absorption bands that are\u0000characteristic of multiple nano-scale OH environments. The use of 2D\u0000diffusion modelling suggests that H diffusion rates in these rocks is as low\u0000as log(D[m2 s−1]) = −24.5 at 540 ∘C. Data were\u0000collected for the main garnet-bearing rock types of the Zermatt–Saas area\u0000allowing a mass balance model of H2O to be calculated. The result shows\u0000that ∼ 3360 kg H2O km−1 (section of oceanic crust) yr−1\u0000could be transported by garnet in the subducting slab beyond 80 km depth and\u0000contributed to the deep-Earth water cycle during the Eocene subduction of\u0000the Piemonte–Liguria Ocean.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42469585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Giulia Marras, G. Carnevale, A. Caracausi, S. Rotolo, V. Stagno
Abstract. The redox state of the Earth's upper mantle (i.e., oxygen fugacity, fO2) is a key variable that influences numerous processes occurring at depth like the mobility of volatile species, partial melting, and metasomatism. It is linked to the oxidation state of peridotite rocks, which is normally determined through the available oxythermobarometers after measuring the chemical composition of equilibrated rock-forming minerals and the Fe3+ in redox-sensitive minerals like spinel or garnet. To date, accurate measurements of Fe3+ / ∑Fe in peridotites have been limited to those peridotites (e.g., harzburgites and lherzolites) for which an oxythermobarometer exists and where spinel (or garnet) crystals can be easily separated and measured by conventional 57Fe Mössbauer spectroscopy. Wehrlitic rocks have been generally formed by the interaction of a lherzolite with carbonatitic melts and, therefore, have recorded the passage of (metasomatic) fluids at mantle conditions. However, no oxythermobarometer exists to determine their equilibrium fO2. The aim of this study was to retrieve the fO2 of the mantle beneath Mt. Vulture volcano (Italy) through the study of a wehrlitic lapillus emitted during the last eruption (∼ 140 kyr ago) that contain olivines with multiple tiny spinel inclusions with sizes < 40 µm. To our knowledge, the Fe oxidation state of these inclusions has been never determined with the Mössbauer technique due to their small sizes. Here, we present measurements of the Fe3+ / ∑Fe using in situ synchrotron Mössbauer spectroscopy coupled with chemical and spectroscopic analysis of both host olivine and spinel inclusions. The results show Fe3+ / ∑Fe ratios of 0.03–0.05 for olivine and 0.40–0.45 for the included spinels, the latter of which appear higher than those reported in literature for mantle spinel harzburgites and lherzolites. Given the evidence of the mantle origin of the trapped spinels, we propose that the high fO2 (between 0.81 and 1.00 log above the fayalite–magnetite–quartz buffer; FMQ) likely results from the interaction between the pristine spinel lherzolite and a CO2-rich metasomatic agent prior to the spinel entrapment in olivines at mantle depths.
{"title":"First measurements of the Fe oxidation state of spinel inclusions in olivine single crystals from Vulture (Italy) with the in situ synchrotron micro-Mössbauer technique","authors":"Giulia Marras, G. Carnevale, A. Caracausi, S. Rotolo, V. Stagno","doi":"10.5194/ejm-35-665-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-665-2023","url":null,"abstract":"Abstract. The redox state of the Earth's upper mantle (i.e., oxygen\u0000fugacity, fO2) is a key variable that influences numerous processes\u0000occurring at depth like the mobility of volatile species, partial melting,\u0000and metasomatism. It is linked to the oxidation state of peridotite rocks,\u0000which is normally determined through the available oxythermobarometers\u0000after measuring the chemical composition of equilibrated rock-forming\u0000minerals and the Fe3+ in redox-sensitive minerals like spinel or\u0000garnet. To date, accurate measurements of Fe3+ / ∑Fe in peridotites\u0000have been limited to those peridotites (e.g., harzburgites and lherzolites) for\u0000which an oxythermobarometer exists and where spinel (or garnet) crystals\u0000can be easily separated and measured by conventional 57Fe Mössbauer\u0000spectroscopy. Wehrlitic rocks have been generally formed by the interaction of a\u0000lherzolite with carbonatitic melts and, therefore, have recorded the passage of\u0000(metasomatic) fluids at mantle conditions. However, no oxythermobarometer\u0000exists to determine their equilibrium fO2. The aim of this study was to retrieve the fO2 of the mantle beneath\u0000Mt. Vulture volcano (Italy) through the study of a wehrlitic lapillus emitted\u0000during the last eruption (∼ 140 kyr ago) that contain olivines\u0000with multiple tiny spinel inclusions with sizes < 40 µm. To\u0000our knowledge, the Fe oxidation state of these inclusions has been never\u0000determined with the Mössbauer technique due to their small sizes. Here, we present measurements of the Fe3+ / ∑Fe using in situ\u0000synchrotron Mössbauer spectroscopy coupled with chemical and\u0000spectroscopic analysis of both host olivine and spinel inclusions. The results show Fe3+ / ∑Fe ratios of 0.03–0.05 for olivine and\u00000.40–0.45 for the included spinels, the latter of which appear higher than\u0000those reported in literature for mantle spinel harzburgites and lherzolites.\u0000Given the evidence of the mantle origin of the trapped spinels, we\u0000propose that the high fO2 (between 0.81 and 1.00 log above the\u0000fayalite–magnetite–quartz buffer; FMQ) likely results from the interaction\u0000between the pristine spinel lherzolite and a CO2-rich metasomatic\u0000agent prior to the spinel entrapment in olivines at mantle depths.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46524999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ferdinando Bosi, Frédéric Hatert, Marco Pasero, Stuart J. Mills
{"title":"IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 74","authors":"Ferdinando Bosi, Frédéric Hatert, Marco Pasero, Stuart J. Mills","doi":"10.5194/ejm-35-659-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-659-2023","url":null,"abstract":"","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136019792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Gilotti, W. McClelland, S. Schorn, R. Compagnoni, M. Coble
Abstract. An eclogite-facies orthogneiss and host paragneiss from a quarry near Tavagnasco in the Lower Aosta Valley were studied in order to refine the protolith, provenance and metamorphic ages of the Eclogitic Micaschist Complex of the Sesia Zone. The orthogneiss contains jadeite with quartz + phengite + K-feldspar ± garnet + rutile + zircon, whereas the paragneiss hosts garnet + jadeite + phengite ± glaucophane + epidote + rutile + quartz. Phase diagram modeling of two representative samples yields minimum equilibration conditions of 550 ± 50 ∘C and 18 ± 2 kbar. Cathodoluminescence images of zircon from the orthogneiss show oscillatory-zoned cores that are embayed and overgrown by complex, oscillatory-zoned rims. Four concordant secondary ion mass spectrometry analyses from the cores give a weighted mean 206Pb / 238U age of 457 ± 5 Ma. The cores have Th/U = 0.1 and negative Eu anomalies indicative of an igneous protolith, which we interpret to have crystallized in the Ordovician at 780 ∘C, based on Ti-in-zircon measurements. Zircon rims yield a range of 206Pb / 238U dates from 74 to 86 Ma, and four concordant analyses define a weighted mean 206Pb / 238U age of 78 ± 2 Ma. The rims are interpreted to have grown in the eclogite facies based on their lower Th/U (0.01), less negative Eu anomalies and steeper heavy rare earth element (HREE) patterns at <600 ∘C. The paragneiss yielded a detrital zircon population with major peaks at 575–600, 655 and 765 Ma; minor older components; and a maximum depositional age of approximately 570 Ma. The prominent Neoproterozoic zircon population and Ediacaran depositional age suggest derivation from the Gondwana margin. The metamorphic zircon is consistent with the oldest eclogite-facies event in the Sesia Zone; it does not show evidence of multiple periods of rim growth or any pre-Alpine (e.g., Variscan) metamorphism.
{"title":"Provenance, protolith and metamorphic ages of jadeite-bearing orthogneiss and host paragneiss at Tavagnasco, the Sesia Zone, Lower Aosta Valley, Italy","authors":"J. Gilotti, W. McClelland, S. Schorn, R. Compagnoni, M. Coble","doi":"10.5194/ejm-35-645-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-645-2023","url":null,"abstract":"Abstract. An eclogite-facies orthogneiss and host paragneiss from a quarry\u0000near Tavagnasco in the Lower Aosta Valley were studied in order to refine\u0000the protolith, provenance and metamorphic ages of the Eclogitic Micaschist\u0000Complex of the Sesia Zone. The orthogneiss contains jadeite with quartz + phengite + K-feldspar ± garnet + rutile + zircon, whereas the\u0000paragneiss hosts garnet + jadeite + phengite ± glaucophane + epidote + rutile + quartz. Phase diagram modeling of two representative\u0000samples yields minimum equilibration conditions of 550 ± 50 ∘C and 18 ± 2 kbar. Cathodoluminescence images of zircon from the\u0000orthogneiss show oscillatory-zoned cores that are embayed and overgrown by\u0000complex, oscillatory-zoned rims. Four concordant secondary ion mass\u0000spectrometry analyses from the cores give a weighted mean\u0000206Pb / 238U age of 457 ± 5 Ma. The cores have Th/U = 0.1\u0000and negative Eu anomalies indicative of an igneous protolith, which we\u0000interpret to have crystallized in the Ordovician at 780 ∘C, based\u0000on Ti-in-zircon measurements. Zircon rims yield a range of\u0000206Pb / 238U dates from 74 to 86 Ma, and four concordant analyses\u0000define a weighted mean 206Pb / 238U age of 78 ± 2 Ma. The rims\u0000are interpreted to have grown in the eclogite facies based on their lower\u0000Th/U (0.01), less negative Eu anomalies and steeper heavy rare\u0000earth element (HREE) patterns at <600 ∘C. The paragneiss yielded a detrital zircon population with\u0000major peaks at 575–600, 655 and 765 Ma; minor older components; and a\u0000maximum depositional age of approximately 570 Ma. The prominent\u0000Neoproterozoic zircon population and Ediacaran depositional age suggest\u0000derivation from the Gondwana margin. The metamorphic zircon is consistent\u0000with the oldest eclogite-facies event in the Sesia Zone; it does not show\u0000evidence of multiple periods of rim growth or any pre-Alpine (e.g.,\u0000Variscan) metamorphism.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43364377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
I. Grey, E. Keck, A. R. Kampf, C. MacRae, R. Gable, W. G. Mumme, N. Wilson, A. Glenn, C. Davidson
Abstract. Hochleitnerite, [K(H2O)]Mn2(Ti2Fe)(PO4)4O2(H2O)10 ⋅ 4H2O, is a new paulkerrite-group mineral from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens of altered zwieselite, in association with fluorapatite, rockbridgeite, columbite and sub-micrometre rods of uranophane. Hochleitnerite occurs as isolated and intergrown pale-yellow, diamond-shaped tablets with thicknesses reaching 50 µm and lengths of 120 µm. The crystals are flattened on {010}, slightly elongated on [001], and bounded by the {111} and {010} forms. The calculated density is 2.40 g cm−3. Optically, hochleitnerite crystals are biaxial (+), with α= 1.615(2), β= 1.621(2) and γ= 1.645(2) (measured in white light). The calculated 2V is 53.8∘. The empirical formula is [K(H2O)](Mn1.512+Fe0.492+)Σ2.00(Ti1.624+Fe0.193+Al0.15)Σ2.96(PO4)4.00[O1.50F0.23(OH)0.27]Σ2.00(H2O)10 ⋅ 4H2O. Hochleitnerite has space group Pbca and unit-cell parameters a= 10.5513(3) Å, b= 20.6855(17) Å, c= 12.4575(4) Å, V= 2718.96(15) Å3 and Z= 4. The crystal structure was refined using single-crystal data to wRobs= 0.082 for 2242 reflections with I > 3σ(I). The crystal structure contains corner-connected linear trimers of Ti-centred octahedra that share corners with PO4 tetrahedra to form 10-member rings parallel to (010). K+ cations and water molecules are located within the rings. Additional corner sharing of the PO4 tetrahedra with MnO2(H2O)4 octahedra occurs along [010] to complete the 3D framework structure.
{"title":"Hochleitnerite, [K(H2O)]Mn2(Ti2Fe)(PO4)4O2(H2O)10 ⋅ 4H2O, a new paulkerrite-group mineral, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany","authors":"I. Grey, E. Keck, A. R. Kampf, C. MacRae, R. Gable, W. G. Mumme, N. Wilson, A. Glenn, C. Davidson","doi":"10.5194/ejm-35-635-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-635-2023","url":null,"abstract":"Abstract. Hochleitnerite,\u0000[K(H2O)]Mn2(Ti2Fe)(PO4)4O2(H2O)10 ⋅ 4H2O, is a new paulkerrite-group mineral from the Hagendorf-Süd\u0000pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens of altered\u0000zwieselite, in association with fluorapatite, rockbridgeite, columbite and\u0000sub-micrometre rods of uranophane. Hochleitnerite occurs as isolated and\u0000intergrown pale-yellow, diamond-shaped tablets with thicknesses reaching 50 µm and lengths of 120 µm. The crystals are flattened on\u0000{010}, slightly elongated on [001], and bounded\u0000by the {111} and {010} forms. The calculated density is\u00002.40 g cm−3. Optically, hochleitnerite crystals are biaxial\u0000(+), with α= 1.615(2), β= 1.621(2) and γ= 1.645(2) (measured in white light). The calculated 2V is 53.8∘.\u0000The empirical formula is\u0000[K(H2O)](Mn1.512+Fe0.492+)Σ2.00(Ti1.624+Fe0.193+Al0.15)Σ2.96(PO4)4.00[O1.50F0.23(OH)0.27]Σ2.00(H2O)10 ⋅ 4H2O. Hochleitnerite has space\u0000group Pbca and unit-cell parameters a= 10.5513(3) Å, b= 20.6855(17) Å,\u0000c= 12.4575(4) Å, V= 2718.96(15) Å3 and Z= 4. The crystal\u0000structure was refined using single-crystal data to wRobs= 0.082 for\u00002242 reflections with I > 3σ(I). The crystal structure\u0000contains corner-connected linear trimers of Ti-centred octahedra that share\u0000corners with PO4 tetrahedra to form 10-member rings parallel to (010).\u0000K+ cations and water molecules are located within the rings. Additional\u0000corner sharing of the PO4 tetrahedra with MnO2(H2O)4\u0000octahedra occurs along [010] to complete the 3D framework structure.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46729512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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