C. Biagioni, F. Bosi, D. Mauro, H. Skogby, A. Dini, F. Zaccarini
Abstract. The new tourmaline supergroup mineral dutrowite, Na(Fe2.52+Ti0.5)Al6(Si6O18)(BO3)3(OH)3O, has been discovered in an outcrop of a Permian metarhyolite near the hamlet of Fornovolasco, Apuan Alps, Tuscany, Italy. It occurs as chemically homogeneous domains, up to 0.5 mm, brown in colour, with a light-brown streak and a vitreous lustre, within anhedral to subhedral prismatic crystals, up to 1 mm in size, closely associated with Fe-rich oxy-dravite. Dutrowite is trigonal, space group R3m, with a=15.9864(8), c=7.2187(4) Å, V=1597.68(18) Å3, and Z=3. The crystal structure was refined to R1=0.0257 for 1095 unique reflections with Fo>4σ (Fo) and 94 refined parameters. Electron microprobe analysis, coupled with Mössbauer spectroscopy, resulted in the empirical structural formula X(Na0.81Ca0.20K0.01)Σ1.02 Y(Fe1.252+Mg0.76Ti0.56Al0.42)Σ3.00 Z(Al4.71Fe0.273+V0.023+Mg0.82Fe0.182+)Σ6.00 T[(Si5.82Al0.18)Σ6.00O18] (BO3)3O(3)(OH)3O(1)[O0.59(OH)0.41]Σ1.00, which was recast in the empirical ordered formula, required for classification purposes: X(Na0.81Ca0.20K0.01)Σ1.02 Y(Fe1.432+Mg1.00Ti0.56)Σ3.00 Z(Al5.13Fe0.273+V0.023+Mg0.58)Σ6.00 T[(Si5.82Al0.18)Σ6.00O18] (BO3)3V(OH)3 W[O0.59(OH)0.41]Σ1.00. Dutrowite is an oxy-species belonging to the alkali group of the tourmaline supergroup. Titanium is hosted in octahedral coordination, and its incorporation is probably due to the substitution 2Al3+ = Ti4+ + (Fe,Mg)2+. Its occurrence seems to be related to late-stage high-T/low-P replacement of “biotite” during the late-magmatic/hydrothermal evolution of the Permian metarhyolite.
{"title":"Dutrowite, Na(Fe2+2.5Ti0.5)Al6(Si6O18)(BO3)3(OH)3O, a new mineral from the Apuan Alps (Tuscany, Italy): the first member of the tourmaline supergroup with Ti as a species-forming chemical constituent","authors":"C. Biagioni, F. Bosi, D. Mauro, H. Skogby, A. Dini, F. Zaccarini","doi":"10.5194/ejm-35-81-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-81-2023","url":null,"abstract":"Abstract. The new tourmaline supergroup mineral dutrowite,\u0000Na(Fe2.52+Ti0.5)Al6(Si6O18)(BO3)3(OH)3O,\u0000has been discovered in an outcrop of a Permian metarhyolite near the hamlet\u0000of Fornovolasco, Apuan Alps, Tuscany, Italy. It occurs as chemically\u0000homogeneous domains, up to 0.5 mm, brown in colour, with a light-brown streak\u0000and a vitreous lustre, within anhedral to subhedral prismatic crystals, up\u0000to 1 mm in size, closely associated with Fe-rich oxy-dravite. Dutrowite is\u0000trigonal, space group R3m, with a=15.9864(8), c=7.2187(4) Å, V=1597.68(18) Å3, and Z=3. The crystal structure was refined to\u0000R1=0.0257 for 1095 unique reflections with Fo>4σ (Fo) and 94 refined parameters. Electron microprobe analysis,\u0000coupled with Mössbauer spectroscopy, resulted in the empirical\u0000structural formula X(Na0.81Ca0.20K0.01)Σ1.02 Y(Fe1.252+Mg0.76Ti0.56Al0.42)Σ3.00 Z(Al4.71Fe0.273+V0.023+Mg0.82Fe0.182+)Σ6.00 T[(Si5.82Al0.18)Σ6.00O18]\u0000(BO3)3O(3)(OH)3O(1)[O0.59(OH)0.41]Σ1.00, which was recast in the\u0000empirical ordered formula, required for classification purposes:\u0000X(Na0.81Ca0.20K0.01)Σ1.02 Y(Fe1.432+Mg1.00Ti0.56)Σ3.00 Z(Al5.13Fe0.273+V0.023+Mg0.58)Σ6.00 T[(Si5.82Al0.18)Σ6.00O18]\u0000(BO3)3V(OH)3 W[O0.59(OH)0.41]Σ1.00. Dutrowite is an\u0000oxy-species belonging to the alkali group of the tourmaline supergroup.\u0000Titanium is hosted in octahedral coordination, and its incorporation is\u0000probably due to the substitution 2Al3+ = Ti4+ + (Fe,Mg)2+. Its occurrence seems to be related to late-stage\u0000high-T/low-P replacement of “biotite” during the\u0000late-magmatic/hydrothermal evolution of the Permian metarhyolite.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45306201","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}
Pete Williams, Frédéric Hatert, Marco Pasero, Stuart Mills
{"title":"IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 71","authors":"Pete Williams, Frédéric Hatert, Marco Pasero, Stuart Mills","doi":"10.5194/ejm-35-75-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-75-2023","url":null,"abstract":"","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136372236","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}
Yanjuan Wang, F. Nestola, Z. Hou, X. Gu, G. Dong, Zhusen Yang, Guang Fan, Zhibin Xiao, Kai Qu
Abstract. A second occurrence of bobtraillite is described from the Gejiu nepheline syenite, southwestern China. The extremely rare and complex boron-bearing zirconium silicate is associated with albite, orthoclase, jadeite, fluorite, andradite, titanite, as well as other REE and zirconium-bearing minerals, catapleiite, moxuanxueite, låvenite, eudialyte, britholite-(Ce), and calcioancylite-(La). The EMP and LA-ICP-MS analyses of the studied material give an empirical formula: (Na9.70Li0.42K0.08□1.80)Σ12.00(Sr10.61Ca1.14Fe0.07□0.18)Σ12.00(Zr12.87Ti0.53Nb0.31REE0.08Y0.06U0.02Th0.01□0.12)Σ14.00(Si42.41B5.59Al0.02)Σ48.02O132(OH)12 ⚫ 12H2O. Bobtraillite is trigonal, with space group P3¯c1, a=19.6977(6), c=9.9770(3) Å, V=3352.4(2) Å3, Z=1. Single-crystal structure refinement revealed that all sodium occupies the Na(1) and Na(2) sites; the site occupancy of these two positions is 0.835(18) and 0.15(2), respectively, suggesting that Na(1) site is Na dominant, while Na(2) is a vacancy-dominant site. The [8]-coordinated site has been assigned to Sr and Ca, with free occupancy factors, 0.874(10) and 0.126(10), respectively. These new data indicate that the ideal formula of bobtraillite could be written as (Na,□)12(□,Na)12Sr12Zr14(Si3O9)10[Si2BO7(OH)2]6 ⚫ 12H2O.
{"title":"Bobtraillite from Gejiu hyperagpaitic nepheline syenite, southwestern China: new occurrence and crystal structure","authors":"Yanjuan Wang, F. Nestola, Z. Hou, X. Gu, G. Dong, Zhusen Yang, Guang Fan, Zhibin Xiao, Kai Qu","doi":"10.5194/ejm-35-65-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-65-2023","url":null,"abstract":"Abstract. A second occurrence of bobtraillite is described from the\u0000Gejiu nepheline syenite, southwestern China. The extremely rare and complex\u0000boron-bearing zirconium silicate is associated with albite, orthoclase,\u0000jadeite, fluorite, andradite, titanite, as well as other REE and\u0000zirconium-bearing minerals, catapleiite, moxuanxueite, låvenite,\u0000eudialyte, britholite-(Ce), and calcioancylite-(La). The EMP and LA-ICP-MS\u0000analyses of the studied material give an empirical formula:\u0000(Na9.70Li0.42K0.08□1.80)Σ12.00(Sr10.61Ca1.14Fe0.07□0.18)Σ12.00(Zr12.87Ti0.53Nb0.31REE0.08Y0.06U0.02Th0.01□0.12)Σ14.00(Si42.41B5.59Al0.02)Σ48.02O132(OH)12 ⚫ 12H2O. Bobtraillite is trigonal,\u0000with space group P3¯c1, a=19.6977(6), c=9.9770(3) Å, V=3352.4(2) Å3, Z=1. Single-crystal structure refinement revealed\u0000that all sodium occupies the Na(1) and Na(2) sites; the site occupancy of\u0000these two positions is 0.835(18) and 0.15(2), respectively, suggesting that\u0000Na(1) site is Na dominant, while Na(2) is a vacancy-dominant site. The\u0000[8]-coordinated site has been assigned to Sr and Ca, with free\u0000occupancy factors, 0.874(10) and 0.126(10), respectively. These new data\u0000indicate that the ideal formula of bobtraillite could be written as\u0000(Na,□)12(□,Na)12Sr12Zr14(Si3O9)10[Si2BO7(OH)2]6 ⚫ 12H2O.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48376475","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. When measuring boron (B) in tourmalines calibrated with schorl, no deviations in the peak intensities could be detected with a proven analysis protocol and using the Mo/B4C multilayer crystal LDEB. It is only when boron is detected in natural and experimental samples, some with significantly lower boron concentrations than in tourmalines, that irregularities in the analysis become visible. This phenomenon is known but has not been analytically investigated so far. Using four natural and artificial solids with boron concentrations from 0.035 wt %–3.14 wt % B, an apparent linear trend line was drawn. The intersect of that trend line with the y axis represents the detection limit of boron, which is of about 0.25 wt % B. The discrepancy between the apparent and the true value trend lines at boron concentrations of 0.25 wt %–2.1 wt % B shows that a correction is necessary. At higher boron concentrations, the discrepancy between the apparent and true value trend lines is within the uncertainty of electron microprobe analysis (EPMA) and disappears completely up to boron concentrations of about 3 wt %.
{"title":"Appearance, study and a possible correction for boron: a phenomenon in ultra-soft X-ray measurements using a synthetic multilayer crystal and the EPMA","authors":"F. Wilke","doi":"10.5194/ejm-35-59-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-59-2023","url":null,"abstract":"Abstract. When measuring boron (B) in tourmalines calibrated with schorl, no deviations in\u0000the peak intensities could be detected with a proven analysis protocol and\u0000using the Mo/B4C multilayer crystal LDEB. It is only when boron is detected\u0000in natural and experimental samples, some with significantly lower boron\u0000concentrations than in tourmalines, that irregularities in the analysis\u0000become visible. This phenomenon is known but has not been analytically\u0000investigated so far. Using four natural and artificial solids with boron\u0000concentrations from 0.035 wt %–3.14 wt % B, an apparent linear trend line was\u0000drawn. The intersect of that trend line with the y axis represents the\u0000detection limit of boron, which is of about 0.25 wt % B. The discrepancy\u0000between the apparent and the true value trend lines at boron concentrations of\u00000.25 wt %–2.1 wt % B shows that a correction is necessary. At higher boron\u0000concentrations, the discrepancy between the apparent and true value\u0000trend lines is within the uncertainty of electron microprobe analysis (EPMA) and disappears\u0000completely up to boron concentrations of about 3 wt %.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46106627","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}
Ashim Rijal, L. Cobden, J. Trampert, H. Marquardt, J. Jackson
Abstract. Shear properties of mantle minerals are vital for interpreting seismic shear wave speeds and therefore inferring the composition and dynamics of a planetary interior. Shear wave speed and elastic tensor components, from which the shear modulus can be computed, are usually measured in the laboratory mimicking the Earth's (or a planet's) internal pressure and temperature conditions. A functional form that relates the shear modulus to pressure (and temperature) is fitted to the measurements and used to interpolate within and extrapolate beyond the range covered by the data. Assuming a functional form provides prior information, and the constraints on the predicted shear modulus and its uncertainties might depend largely on the assumed prior rather than the data. In the present study, we propose a data-driven approach in which we train a neural network to learn the relationship between the pressure, temperature and shear modulus from the experimental data without prescribing a functional form a priori. We present an application to MgO, but the same approach works for any other mineral if there are sufficient data to train a neural network. At low pressures, the shear modulus of MgO is well-constrained by the data. However, our results show that different experimental results are inconsistent even at room temperature, seen as multiple peaks and diverging trends in probability density functions predicted by the network. Furthermore, although an explicit finite-strain equation mostly agrees with the likelihood predicted by the neural network, there are regions where it diverges from the range given by the networks. In those regions, it is the prior assumption of the form of the equation that provides constraints on the shear modulus regardless of how the Earth behaves (or data behave). In situations where realistic uncertainties are not reported, one can become overconfident when interpreting seismic models based on those defined equations of state. In contrast, the trained neural network provides a reasonable approximation to experimental data and quantifies the uncertainty from experimental errors, interpolation uncertainty, data sparsity and inconsistencies from different experiments.
{"title":"Shear properties of MgO inferred using neural networks","authors":"Ashim Rijal, L. Cobden, J. Trampert, H. Marquardt, J. Jackson","doi":"10.5194/ejm-35-45-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-45-2023","url":null,"abstract":"Abstract. Shear properties of mantle minerals are vital for interpreting seismic shear wave speeds and therefore inferring the composition and dynamics of a planetary interior. Shear wave speed and elastic tensor components, from which the shear modulus can be computed, are usually measured in the laboratory mimicking the Earth's (or a planet's) internal pressure and temperature conditions. A functional form that relates the shear modulus to pressure (and temperature) is fitted to the measurements and used to interpolate within and extrapolate beyond the range covered by the data. Assuming a functional form provides prior information, and the constraints on the predicted shear modulus and its uncertainties might depend largely on the assumed prior rather than the data. In the present study, we propose a data-driven approach in which we train a neural network to learn the relationship between the pressure, temperature and shear modulus from the experimental data without prescribing a functional form a priori. We present an application to MgO, but the same approach works for any other mineral if there are sufficient data to train a neural network. At low pressures, the shear modulus of MgO is well-constrained by the data. However, our results show that different experimental results are inconsistent even at room temperature, seen as multiple peaks and diverging trends in probability density functions predicted by the network. Furthermore, although an explicit finite-strain equation mostly agrees with the likelihood predicted by the neural network, there are regions where it diverges from the range given by the networks. In those regions, it is the prior assumption of the form of the equation that provides constraints on the shear modulus regardless of how the Earth behaves (or data behave). In situations where realistic uncertainties are not reported, one can become overconfident when interpreting seismic models based on those defined equations of state. In contrast, the trained neural network provides a reasonable approximation to experimental data and quantifies the uncertainty from experimental errors, interpolation uncertainty, data sparsity and inconsistencies from different experiments.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45618885","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. Authigenic epidote supergroups are an abundant accessory mineral in the calcium–aluminum silicate and thermometamorphic hydrothermal zones of the Campi Flegrei (Phlegraean Fields) geothermal field located west of Naples, Italy. Geothermal exploration for high-enthalpy fluid produced drill core and cuttings to ∼ 3 km depth in the Mofete (MF1, MF2, MF5) and San Vito (SV1, SV3) wells, where measured down-hole temperatures of epidote-bearing samples range from 270–350 ∘C and from 285–390 ∘C for the Mofete and San Vito areas, respectively. Two epidote group (epidote, clinozoisite), some rare earth element (REE)-bearing, and two allanite group (allanite-(Ce), ferriallanite-(Ce)) minerals were identified by electron microprobe. The allanite group is light rare earth element (LREE, La–Gd) enriched, Ce dominant, with REE + Y that varies from 30.59 wt %–14.32 wt %. Complex compositional variation such as oscillatory, sector, and complex (mixed) zoning is a ubiquitous feature observed in the epidote group, which occurs as veins, in vugs, as various size masses, and as isolated single crystals. Compositional zoning is caused by variable Fe ↔ Al3+ substitution and XFe [(Fe3+) / (Fe3++ Al)] ranges from 0.06–0.33 (Fe3+=0.185–0.967 apfu). XFe tends to decrease with increasing temperature in the Mofete wells, but its distribution is more complex in the San Vito wells, which records recent fault displacement. The variety and complexity of the epidote supergroup zoning suggest rapid fluid composition and/or intensive parameter fluctuations in the local hydrothermal system.
{"title":"Compositional variation and zoning of epidote supergroup minerals in the Campi Flegrei geothermal field, Naples, Italy","authors":"H. Belkin, B. De Vivo","doi":"10.5194/ejm-35-25-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-25-2023","url":null,"abstract":"Abstract. Authigenic epidote supergroups are an abundant accessory mineral in the\u0000calcium–aluminum silicate and thermometamorphic hydrothermal zones of the\u0000Campi Flegrei (Phlegraean Fields) geothermal field located west of Naples,\u0000Italy. Geothermal exploration for high-enthalpy fluid produced drill core\u0000and cuttings to ∼ 3 km depth in the Mofete (MF1, MF2, MF5) and\u0000San Vito (SV1, SV3) wells, where measured down-hole temperatures of\u0000epidote-bearing samples range from 270–350 ∘C and from\u0000285–390 ∘C for the Mofete and San Vito areas, respectively. Two\u0000epidote group (epidote, clinozoisite), some rare earth element\u0000(REE)-bearing, and two allanite group (allanite-(Ce), ferriallanite-(Ce))\u0000minerals were identified by electron microprobe. The allanite group is light\u0000rare earth element (LREE, La–Gd) enriched, Ce dominant, with REE + Y that\u0000varies from 30.59 wt %–14.32 wt %. Complex compositional variation such as\u0000oscillatory, sector, and complex (mixed) zoning is a ubiquitous feature\u0000observed in the epidote group, which occurs as veins, in vugs, as various\u0000size masses, and as isolated single crystals. Compositional zoning is caused\u0000by variable Fe ↔ Al3+ substitution and XFe [(Fe3+) / (Fe3++ Al)] ranges from 0.06–0.33 (Fe3+=0.185–0.967 apfu). XFe tends to decrease with increasing temperature\u0000in the Mofete wells, but its distribution is more complex in the San Vito\u0000wells, which records recent fault displacement. The variety and complexity\u0000of the epidote supergroup zoning suggest rapid fluid composition and/or\u0000intensive parameter fluctuations in the local hydrothermal system.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"1 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71223644","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. In the Variscan lower–intermediate crust exposed in the Palmi area (southwestern Calabria, Italy), amphibolites occur as foliated, decimeter-thick layers within migmatitic paragneiss and as a decametric main body adjacent to the migmatites. The main body is mostly fine-grained and weakly to moderately foliated; unfoliated medium-grained portions rarely occur. Amphibolites are mainly composed of plagioclase (An80−91) frequently developing triple junctions, amphibole consisting of cummingtonite rimmed by hornblende and variable amounts of biotite. Minor quartz is present in amphibolite layers within paragneiss. Accessory allanite occurs in amphibolite layers within migmatites and in foliated, fine-grained portions from the main body. This study mainly aims to achieve information about the effects triggered by the migration of migmatite-related melts into associated mafic rocks and its role in the re-distribution of major and trace elements out of the anatectic source. On the basis of whole-rock major- and trace-element compositions, the protolith of amphibolite is recognized as of cumulus origin, likely derived from basic melt emplaced in the framework of the late-Variscan lithospheric extension. The rocks experienced high-temperature subsolidus re-equilibration (∼800 ∘C) in conjunction with the development of amphibole. The origin of amphibole is attributed to a coupled dissolution–precipitation process related to the reaction between migrating SiO2-rich hydrous melt and precursor orthopyroxene (± plagioclase). Reactive melt migration also caused the crystallization of biotite ± allanite ± quartz ± plagioclase. SiO2-rich hydrous melt had REE (rare earth element) compositions similar to late-Variscan peraluminous granites and could have been derived by partial melting of metasediments akin to neighboring migmatitic paragneisses. Both whole-rock and amphibole analyses reveal a decrease in Mg# (Mg/(Mg+Fe2+)) from amphibolite layers within paragneiss to fine- and medium-grained rocks of the main body. Hornblende shows an increase in SiO2 and a decrease in Al2O3 and K2O with increasing Mg#. Amphibolites interlayered with paragneiss have higher K2O, Rb, Ba, Th, U and Zr relative to those from the main body. Furthermore, amphibole from amphibolites interlayered with paragneiss is distinct for relatively high Rb, Ba, MREE (middle rare earth element) and HREE (heavy rare earth element) concentrations. Within the main body, foliated, fine-grained rock has both the whole rock and amphibole enriched in Rb and Ba and high Zr bulk-rock contents. Whole-rock and mineral chemistry heterogeneity most likely reflects (i) variation of the composition of the melt during its reactive migration, in response to dissolution of pre-existing minerals and crystallization of new phases, and (ii) variable modification of the original compositions. Foliated and fine-grained amphibolites record the strongest modification, thereby suggesting that they represent permeabl
{"title":"Reactive interaction between migmatite-related melt and mafic rocks: clues from the Variscan lower crust of Palmi (southwestern Calabria, Italy)","authors":"M. Renna","doi":"10.5194/ejm-35-1-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-1-2023","url":null,"abstract":"Abstract. In the Variscan lower–intermediate crust exposed in the Palmi area (southwestern\u0000Calabria, Italy), amphibolites occur as foliated, decimeter-thick layers\u0000within migmatitic paragneiss and as a decametric main body adjacent to the\u0000migmatites. The main body is mostly fine-grained and weakly to moderately\u0000foliated; unfoliated medium-grained portions rarely occur. Amphibolites are\u0000mainly composed of plagioclase (An80−91) frequently developing triple\u0000junctions, amphibole consisting of cummingtonite rimmed by hornblende and\u0000variable amounts of biotite. Minor quartz is present in amphibolite layers\u0000within paragneiss. Accessory allanite occurs in amphibolite layers within\u0000migmatites and in foliated, fine-grained portions from the main body. This\u0000study mainly aims to achieve information about the effects triggered by the\u0000migration of migmatite-related melts into associated mafic rocks and its\u0000role in the re-distribution of major and trace elements out of the anatectic\u0000source. On the basis of whole-rock major- and trace-element compositions, the\u0000protolith of amphibolite is recognized as of cumulus origin, likely derived\u0000from basic melt emplaced in the framework of the late-Variscan lithospheric\u0000extension. The rocks experienced high-temperature subsolidus\u0000re-equilibration (∼800 ∘C) in conjunction with the\u0000development of amphibole. The origin of amphibole is attributed to a coupled\u0000dissolution–precipitation process related to the reaction between migrating\u0000SiO2-rich hydrous melt and precursor orthopyroxene (± plagioclase). Reactive melt migration also caused the crystallization of\u0000biotite ± allanite ± quartz ± plagioclase. SiO2-rich\u0000hydrous melt had REE (rare earth element) compositions similar to late-Variscan peraluminous\u0000granites and could have been derived by partial melting of metasediments\u0000akin to neighboring migmatitic paragneisses. Both whole-rock and amphibole analyses reveal a decrease in Mg# (Mg/(Mg+Fe2+)) from\u0000amphibolite layers within paragneiss to fine- and medium-grained rocks of\u0000the main body. Hornblende shows an increase in SiO2 and a decrease in\u0000Al2O3 and K2O with increasing Mg#. Amphibolites\u0000interlayered with paragneiss have higher K2O, Rb, Ba, Th, U and Zr\u0000relative to those from the main body. Furthermore, amphibole from\u0000amphibolites interlayered with paragneiss is distinct for relatively high\u0000Rb, Ba, MREE (middle rare earth element) and HREE (heavy rare earth element) concentrations. Within the main body, foliated,\u0000fine-grained rock has both the whole rock and amphibole enriched in Rb and Ba\u0000and high Zr bulk-rock contents. Whole-rock and mineral chemistry\u0000heterogeneity most likely reflects (i) variation of the composition of the\u0000melt during its reactive migration, in response to dissolution of\u0000pre-existing minerals and crystallization of new phases, and (ii) variable\u0000modification of the original compositions. Foliated and fine-grained\u0000amphibolites record the strongest modification, thereby suggesting that they\u0000represent permeabl","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49444530","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}
E. Balan, L. Paulatto, Qianyu Deng, K. Béneut, M. Guillaumet, B. Baptiste
Abstract. The near-infrared (NIR) spectra of hydrous minerals display absorption bands involving multiple excitations of vibrational modes. They usually involve OH stretching modes, but their interpretation is not straightforward due to the combined effects of bond anharmonicity and vibrational coupling. In the present study, the mid-infrared (MIR) and near-infrared spectra of well-ordered samples of trioctahedral layered hydrous minerals, talc, brucite and lizardite, have been measured on a spectral range extending from the fundamental vibrational modes to the second OH stretching overtones. The bands corresponding to molecular overtones are interpreted using an effective approach allowing us to infer the anharmonicity and coupling parameters controlling the OH stretching frequencies from spectroscopic data. They follow the usual relation between transition energy and quantum number of the excited state, which facilitates the comparison of NIR and MIR spectra. The results support the assignment of the main overtone bands to specific environments of OH groups and bring new constraints for the identification of the vibrational bands related to Fe and Al substitutions at octahedral sites in serpentines. The two-phonon absorption bands are theoretically analyzed at the density functional theory level by computing the absorption arising from the self-energy of the IR-active vibrational modes. The characteristics of the two-phonon OH stretching continuum between 7300 and 7400 cm−1 and of the combination bands between 4000 and 4800 cm−1 are related to the specificities of the one-phonon and two-phonon densities of states of the three minerals.
{"title":"Molecular overtones and two-phonon combination bands in the near-infrared spectra of talc, brucite and lizardite","authors":"E. Balan, L. Paulatto, Qianyu Deng, K. Béneut, M. Guillaumet, B. Baptiste","doi":"10.5194/ejm-34-627-2022","DOIUrl":"https://doi.org/10.5194/ejm-34-627-2022","url":null,"abstract":"Abstract. The near-infrared (NIR) spectra of hydrous minerals display absorption bands\u0000involving multiple excitations of vibrational modes. They usually involve OH\u0000stretching modes, but their interpretation is not straightforward due to the\u0000combined effects of bond anharmonicity and vibrational coupling. In the\u0000present study, the mid-infrared (MIR) and near-infrared spectra of\u0000well-ordered samples of trioctahedral layered hydrous minerals, talc,\u0000brucite and lizardite, have been measured on a spectral range extending\u0000from the fundamental vibrational modes to the second OH stretching\u0000overtones. The bands corresponding to molecular overtones are interpreted\u0000using an effective approach allowing us to infer the anharmonicity and coupling\u0000parameters controlling the OH stretching frequencies from spectroscopic data.\u0000They follow the usual relation between transition energy and quantum number\u0000of the excited state, which facilitates the comparison of NIR and MIR\u0000spectra. The results support the assignment of the main overtone bands to\u0000specific environments of OH groups and bring new constraints for the\u0000identification of the vibrational bands related to Fe and Al substitutions\u0000at octahedral sites in serpentines. The two-phonon absorption bands are\u0000theoretically analyzed at the density functional theory level by computing\u0000the absorption arising from the self-energy of the IR-active vibrational\u0000modes. The characteristics of the two-phonon OH stretching continuum between\u00007300 and 7400 cm−1 and of the combination bands between 4000 and 4800 cm−1 are related to the specificities of the one-phonon and two-phonon\u0000densities of states of the three minerals.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2022-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46464872","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 ferric iron content in hydrothermally altered ultrabasic rocks and their major minerals, serpentines and Mg-chlorites, is important for establishing the oxidation state budget from oceanic ridges to subduction zones, in carbonaceous chondrites, and for modeling phase equilibria. A compilation of literature Mössbauer spectroscopic data on serpentines and magnesian chlorites from high-pressure ophiolites yields much lower ferric-to-total-iron ratios (Fe3+ / Fetotal) than those obtained on similar samples by X-ray absorption near-edge spectroscopy (XANES), leading to contradictory estimates of the ferric iron budget of subduction zones. New Mössbauer analysis of antigorite and Mg-chlorite samples from suites of high-pressure ophiolitic terrains of various Phanerozoic ages confirms the low and homogeneous values previously obtained by this technique, while lizardite inherited from oceanic hydrothermal alteration is ferric iron rich. We argue that XANES values may be biased by photo-oxidation when samples have a high Mg content, which is the case for serpentines and chlorites from subduction zones. Photo-oxidation is less important in Fe-poor phyllosilicates of the mica and talc families and does not affect the Fe-rich serpentines (greenalite, cronstedtite) of meteorites or Fe-rich terrestrial phyllosilicates. Mössbauer Fe3+ / Fetotal ratios of serpentine confirm the occurrence of a major redox change at the lizardite–antigorite transition near 300–400 ∘C rather than at the dehydration of antigorite at 500–650 ∘C in serpentinites from high-pressure ophiolites.
{"title":"Iron oxidation state in serpentines and magnesian chlorites of subduction-related rocks","authors":"B. Reynard, C. Fellah, C. McCammon","doi":"10.5194/ejm-34-645-2022","DOIUrl":"https://doi.org/10.5194/ejm-34-645-2022","url":null,"abstract":"Abstract. The ferric iron content in hydrothermally altered ultrabasic rocks and their major minerals, serpentines and Mg-chlorites, is important for establishing the oxidation state budget from oceanic ridges to subduction zones, in carbonaceous chondrites, and for modeling phase equilibria. A compilation of literature Mössbauer spectroscopic data on serpentines and magnesian chlorites from high-pressure ophiolites yields much lower ferric-to-total-iron ratios (Fe3+ / Fetotal) than those obtained on similar samples by X-ray absorption near-edge spectroscopy (XANES), leading to contradictory estimates of the ferric iron budget of subduction zones. New Mössbauer analysis of antigorite and Mg-chlorite samples from suites of high-pressure ophiolitic terrains of various Phanerozoic ages confirms the low and homogeneous values previously obtained by this technique, while lizardite inherited from oceanic hydrothermal alteration is ferric iron rich. We argue that XANES values may be biased by photo-oxidation when samples have a high Mg content, which is the case for serpentines and chlorites from subduction zones. Photo-oxidation is less important in Fe-poor phyllosilicates of the mica and talc families and does not affect the Fe-rich serpentines (greenalite, cronstedtite) of meteorites or Fe-rich terrestrial phyllosilicates. Mössbauer Fe3+ / Fetotal ratios of serpentine confirm the occurrence of a major redox change at the lizardite–antigorite transition near 300–400 ∘C rather than at the dehydration of antigorite at 500–650 ∘C in serpentinites from high-pressure ophiolites.","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"1 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2022-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41365226","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}
Artur Engelhardt, J. Koepke, Chao Zhang, D. Garbe‐Schönberg, A. Jesus
Abstract. The Oman ophiolite (Samail massif, Sultanate of Oman) is the largest sub-aerial exposure of oceanic lithosphere on Earth and provides the opportunity to study the accretion and alteration of oceanic lithosphere formed under fast-spreading conditions. Drill hole GT3A (23∘06′50.7′′ N, 58∘12′42.2′′ E) of the ICDP (International Continental Scientific Drilling Program) Oman Drilling Project with a length of 400 m aimed at penetrating the dike–gabbro transition of the Samail ophiolite paleocrust in order to shed light on the role of the axial melt lens (AML) during accretion of the lower plutonic crust. AMLs beneath fast-spreading mid-ocean ridges are sandwiched between the sheeted dike complex and the uppermost gabbros and are believed to feed the upper crust and, at least partially, the underlying crystal mush. Typical gabbroic rocks from dike–gabbro transitions of fast-spreading systems are the so-called “varitextured gabbros”, often showing considerable variations in mineral mode, texture and grain size, which are regarded as the frozen fillings of axial melt lenses. Here, we present a detailed petrographic, microanalytical and bulk-chemical investigation of 36 mafic rocks from the drill hole GT3A, which represent mostly varitextured gabbros, revealing a complex formation with several evolution stages. Poikilitic domains formed first, corresponding to an early crystallization stage, where only plagioclase and clinopyroxene of more primitive composition crystallized. Later, domains of granular textures containing also interstitial amphibole and Fe–Ti oxide were formed. This stage is characterized by a magma evolution that underwent crystal fractionation established by lower temperatures due to more efficient hydrothermal cooling at the margin of the AML. A last stage is characterized by pervasive hydrothermal alteration, where all primary minerals have been altered under temperature conditions, varying from the magmatic regime down to greenschist facies. A highlight of this stage is amphiboles showing noticeable compositional zoning. The observation of peculiar microgranular domains, representing relics of stoped exogenic material from the sheeted dike complex, documents the upward migration of an AML in a replenishment event, forcing the AML to burn through previously altered sheeted dikes. This process is responsible for significant assimilation of hydrothermally altered components, indicated by a marked Cl enrichment in the outer zones of magmatic amphiboles. Petrological modeling involving gabbros and basalts revealed that the GT3A rock suite followed a fractional crystallization evolution trend, with a primitive MORB as parental melt with an estimated water content of 0.2 wt % to 0.8 wt %. The modeled liquid lines of descent suggest a magmatic evolution via fractional crystallization, where the basalts correspond to frozen liquids, while the gabbros, especially the more primitive ones, show a significant cumulate component.
{"title":"ICDP Oman Drilling Project: varitextured gabbros from the dike–gabbro transition within drill core GT3A","authors":"Artur Engelhardt, J. Koepke, Chao Zhang, D. Garbe‐Schönberg, A. Jesus","doi":"10.5194/ejm-34-603-2022","DOIUrl":"https://doi.org/10.5194/ejm-34-603-2022","url":null,"abstract":"Abstract. The Oman ophiolite (Samail massif, Sultanate of Oman) is the\u0000largest sub-aerial exposure of oceanic lithosphere on Earth and provides the\u0000opportunity to study the accretion and alteration of oceanic lithosphere\u0000formed under fast-spreading conditions. Drill hole GT3A (23∘06′50.7′′ N, 58∘12′42.2′′ E) of the ICDP (International Continental\u0000Scientific Drilling Program) Oman Drilling Project with a length of 400 m\u0000aimed at penetrating the dike–gabbro transition of the Samail ophiolite\u0000paleocrust in order to shed light on the role of the axial melt lens (AML)\u0000during accretion of the lower plutonic crust. AMLs beneath fast-spreading\u0000mid-ocean ridges are sandwiched between the sheeted dike complex and the\u0000uppermost gabbros and are believed to feed the upper crust and, at least\u0000partially, the underlying crystal mush. Typical gabbroic rocks from dike–gabbro transitions of fast-spreading\u0000systems are the so-called “varitextured gabbros”, often showing\u0000considerable variations in mineral mode, texture and grain size, which are\u0000regarded as the frozen fillings of axial melt lenses. Here, we present a\u0000detailed petrographic, microanalytical and bulk-chemical investigation of 36\u0000mafic rocks from the drill hole GT3A, which represent mostly varitextured\u0000gabbros, revealing a complex formation with several evolution stages.\u0000Poikilitic domains formed first, corresponding to an early crystallization\u0000stage, where only plagioclase and clinopyroxene of more primitive\u0000composition crystallized. Later, domains of granular textures containing\u0000also interstitial amphibole and Fe–Ti oxide were formed. This stage is\u0000characterized by a magma evolution that underwent crystal fractionation\u0000established by lower temperatures due to more efficient hydrothermal\u0000cooling at the margin of the AML. A last stage is characterized by pervasive\u0000hydrothermal alteration, where all primary minerals have been altered under\u0000temperature conditions, varying from the magmatic regime down to greenschist\u0000facies. A highlight of this stage is amphiboles showing noticeable\u0000compositional zoning. The observation of peculiar microgranular domains,\u0000representing relics of stoped exogenic material from the sheeted dike\u0000complex, documents the upward migration of an AML in a replenishment event,\u0000forcing the AML to burn through previously altered sheeted dikes. This\u0000process is responsible for significant assimilation of hydrothermally\u0000altered components, indicated by a marked Cl enrichment in the outer zones\u0000of magmatic amphiboles. Petrological modeling involving gabbros and basalts\u0000revealed that the GT3A rock suite followed a fractional crystallization\u0000evolution trend, with a primitive MORB as parental melt with an estimated\u0000water content of 0.2 wt % to 0.8 wt %. The modeled liquid lines of descent\u0000suggest a magmatic evolution via fractional crystallization, where the\u0000basalts correspond to frozen liquids, while the gabbros, especially the more\u0000primitive ones, show a significant cumulate component.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2022-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41409302","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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