European Journal of Mineralogy最新文献

{"title":"Effect of oxygen fugacity on the storage of water in wadsleyite and olivine in H and H–C fluids and implications for melting atop the transition zone","authors":"N. Bolfan-Casanova, L. Martinek, G. Manthilake, M. Verdier-Paoletti, P. Chauvigne","doi":"10.5194/ejm-35-549-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-549-2023","url":null,"abstract":"Abstract. This study aims to experimentally constrain the water storage capacities of\u0000olivine and wadsleyite at a depth near 410 km (12–14 GPa) under\u0000water-saturated conditions, as a function of temperature, oxygen fugacity,\u0000and the presence of carbon (molar H / C of 2). Experiments have been conducted\u0000in the multi-anvil press, with sealed double capsules to preserve fluids, at\u00001200 to 1400 ∘C and three different oxygen fugacities fixed at the\u0000rhenium–rhenium oxide buffer (RRO), nickel–nickel oxide buffer (NNO), and\u0000iron-wüstite (IW) for oxidizing, intermediate, and reducing conditions,\u0000respectively. The water contents of minerals were measured by Raman\u0000spectroscopy that allows a very small beam size to be used and were\u0000cross-checked on a few samples with NanoSIMS analyses. We observe an effect, although slight, of fO2 on the water storage\u0000capacity of both wadsleyite and olivine and also on their solidus\u0000temperatures. At 1200 ∘C, the storage capacity of the nominally anhydrous\u0000minerals (NAMS)\u0000increases with increasing oxygen fugacity (from the IW to the RRO buffer)\u0000from 1 wt % to 1.5 wt % H2O in wadsleyite and from 0.1 wt % to 0.2 wt % in olivine, owing to the increase in H2O / H2 speciation in\u0000the fluid, whereas at 1400 ∘C the storage capacity decreases from\u00001 wt % to 0.75 wt % H2O in wadsleyite and down to 0.03 wt % for\u0000olivine. At high temperature, the water storage capacity is lowered due to\u0000melting, and the more oxidized the conditions are the more the solidus is\u0000depressed. Still, at 1400 ∘C and IW, wadsleyite can store\u0000substantial amounts of water: 0.8 wt % to 1 wt % H2O. The effect of carbon is\u0000to decrease water storage capacity in both wadsleyite and olivine by an\u0000average factor 2 at 1300–1400 ∘C. The trends in water storage as a\u0000function of fO2 and C presence are confirmed by NanoSIMS measurements.\u0000The solidus at IW without C is located between 1300 and 1400 ∘C in\u0000the wadsleyite stability field and drops to temperatures below 1300 ∘C in the olivine stability field. With the addition of C, the\u0000solidus is found between 1200 and 1300 ∘C in both olivine and\u0000wadsleyite stability fields.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47140868","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}

{"title":"Some thoughts about eclogites and related rocks","authors":"Michael Brown","doi":"10.5194/ejm-35-523-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-523-2023","url":null,"abstract":"Abstract. The past 40 years have been a golden age for eclogite\u0000studies, supported by an ever wider range of instrumentation and enhanced\u0000computational capabilities, linked with ongoing developments in\u0000thermobarometry and geochronology. During this time, we have made robust\u0000estimates of pressure–temperature (P–T) conditions; determined ages related to\u0000the prograde, metamorphic peak and retrograde stages; and calculated time-integrated rates of cooling and exhumation for eclogites and related rocks,\u0000including blueschists, from orogenic belts worldwide. Improvements to single\u0000mineral thermometers and new developments in elastic barometry using\u0000inclusions of one mineral in another (e.g. quartz and/or zircon in garnet),\u0000coupled with ongoing innovations in petrochronology and diffusion modelling,\u0000presage a new age for eclogite studies in which detailed quantification of\u0000metamorphic conditions and timescales will be linked to an improved\u0000understanding of processes at all scales. Since the turn of the century,\u0000numerical modelling of subduction zone and rock exhumation processes has\u0000become increasingly important. As a result, subduction and exhumation are\u0000quite well understood, but the volume of continental crust subducted to and\u0000returned from mantle conditions and the amount lost to the mantle are\u0000largely unknown. We have generated sufficient data to investigate the\u0000spatiotemporal distribution of metamorphism and secular change but not\u0000without controversy in relation to the rare occurrence of orogenic eclogites\u0000and the absence of blueschists prior to the late Neoproterozoic and the\u0000emergence of plate tectonics on Earth. Since the turn of the century, the\u0000assumption that metamorphic pressure is lithostatic has come under\u0000increasing scrutiny. Whether local variations in stress extrapolate to the\u0000crustal scale and, if so, whether the magnitude of the calculated deviations\u0000from lithostatic pressure can be generated and sustained in mechanically\u0000heterogeneous rock units remains contentious. Could the paradigm of\u0000subduction of continental lithosphere to mantle depths be simply an artefact\u0000of the lithostatic assumption? Fluid cycling in subduction zones and\u0000understanding the role of fluids in the generation of intermediate-depth\u0000earthquakes remain important topics of current research. Dry (H2O-absent) conditions are unlikely around the peak of ultrahigh-pressure (UHP) metamorphism or\u0000during exhumation, due to dehydroxylation of nominally anhydrous minerals\u0000and breakdown of hydrous minerals at P–T conditions in the realm of\u0000supercritical fluid and hydrous melt. Indeed, the presence of melt may be\u0000necessary to facilitate the exhumation of HP and UHP tectonometamorphic\u0000rock units. Finally, our ability to interrogate inclusions in superdeep\u0000diamonds should lead to a better understanding of how the deep interior and\u0000surface are linked in the context of Earth as a fully coupled system.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45898429","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}

{"title":"Metamorphic P–T paths of Archean granulite facies metasedimentary lithologies from the eastern Beartooth Mountains of the northern Wyoming Province, Montana, USA: constraints from quartz-in-garnet (QuiG) Raman elastic barometry, geothermobarometry, and thermodynamic modeling","authors":"L. Tuttle, D. Henry","doi":"10.5194/ejm-35-499-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-499-2023","url":null,"abstract":"Abstract. Metamorphic pressure and temperature (P–T) paths in late-Archean\u0000high-grade rocks of the eastern Beartooth Mountains of Montana (USA), a\u0000portion of the Wyoming Province, are established by a combination of\u0000imaging, analytical, and modeling approaches. Garnet inclusion mechanical\u0000and chemical thermobarometry, applied to several granulite-facies migmatites\u0000and an iron formation, is particularly useful in constraining the prograde\u0000P–T conditions. Quartz-in-garnet (QuiG) elastic Raman barometry was used on\u0000quartz inclusions in garnet for all samples studied. For a smaller subset of\u0000four representative samples, QuiG constraints were used in conjunction with\u0000Ti-in-quartz (TitaniQ) and Ti-in-biotite (TiB) thermometry to establish\u0000unique prograde inclusion entrapment P–T conditions. Ti measurements of\u0000garnet hosts and cathodoluminescence (CL) imagery of inclusion and matrix\u0000quartz grains were employed to check for Ti loss/diffusion. Lastly,\u0000inclusion studies were supplemented with thermodynamic modeling and matrix\u0000chemical thermobarometry to examine garnet nucleation temperatures and peak\u0000metamorphic conditions. Disagreement between the volume strain and elastic tensor methods used to\u0000calculate quartz inclusion pressures implies that quartz inclusions studied\u0000are under strong differential strain. Prograde entrapment results from the\u0000two inclusion thermobarometry pairs used are distinct: 0.55–0.70 GPa and\u0000475–580 ∘C (QuiG–TitaniQ) versus 0.85–1.10 GPa and 665–780 ∘C (QuiG–TiB). Garnet modal isopleth modeling indicates that the\u0000majority of garnet growth occurred at ∼ 450–600 ∘C,\u0000implying that P–T conditions of garnet growth are interpreted to be most\u0000reliably represented by QuiG–TitaniQ inclusion thermobarometry. Normal\u0000distributions of calculated QuiG inclusion pressures and the concentration\u0000of mineral inclusions in garnet cores suggest that the majority of garnet\u0000inclusions were entrapped during a single stage of porphyroblast growth. A\u0000general lack of evidence from CL imagery for post-entrapment mechanical or\u0000chemical modifications to quartz inclusions suggests that quartz inclusions\u0000used to calculate entrapment P–T largely preserve their initial entrapment\u0000conditions. Biotite inclusions preserve higher temperatures than quartz\u0000inclusions in the same garnets, likely due to Fe–Mg exchange with garnet\u0000hosts that allowed Ti content of biotite to change after entrapment.\u0000Pseudosection modeling and matrix chemical thermobarometry of multiple,\u0000independent lithologies examined during inclusion studies suggest a range of\u0000peak granulite facies conditions of ∼ 0.50–0.70 GPa and\u0000730–800 ∘C. Peak metamorphic P–T modeling work from this study,\u0000together with evidence of regional amphibolite facies overprinting in\u0000immediately adjacent samples, indicates an overall clockwise metamorphic P–T\u0000path with nearly isobaric prograde heating to peak temperatures. Interpreted\u0000P–T path reconstructions are consistent with metamorphism developed in a\u0000more modern-style co","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48880543","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}

{"title":"Detrital garnet petrology challenges Paleoproterozoic ultrahigh-pressure metamorphism in western Greenland","authors":"J. Schönig, Carsten Benner, G. Meinhold, H. von Eynatten, N. K. Lünsdorf","doi":"10.5194/ejm-35-479-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-479-2023","url":null,"abstract":"Abstract. Modern-style plate tectonics is characterised by the\u0000global operation of cold and deep subduction involving blueschist facies and\u0000ultrahigh-pressure metamorphism. This has been a common process since the\u0000Neoproterozoic, but a couple of studies indicate similar processes were\u0000active in the Paleoproterozoic, at least on the local scale. Particularly\u0000conspicuous are extreme ultrahigh-pressure conditions of ∼ 7 GPa at thermal gradients < 150 ∘C GPa−1 proposed for\u0000metamorphic rocks of the Nordre Strømfjord shear zone in the western part\u0000of the Paleoproterozoic Nagssugtoqidian Orogen of Greenland. By acquiring a\u0000large dataset of heavy minerals (n = 52 130) and garnet major-element\u0000composition integrated with mineral inclusion analysis (n=2669) from\u0000modern sands representing fresh and naturally mixed erosional material from\u0000the metamorphic rocks, we here intensely screened the area for potential\u0000occurrences of ultrahigh-pressure rocks and put constraints on the\u0000metamorphic evolution. Apart from the absence of any indications pointing to\u0000ultrahigh-pressure and low-temperature–high-pressure metamorphism, the\u0000results are well in accordance with a common Paleoproterozoic\u0000subduction–collision metamorphic evolution along a Barrovian-type\u0000intermediate temperature and pressure gradient with a pressure peak at the\u0000amphibolite–granulite–eclogite-facies transition and a temperature peak\u0000at medium- to high-pressure granulite-facies conditions. In addition, we\u0000discuss that all “evidence” for ultrahigh-pressure metamorphism proposed\u0000in the literature for rocks of this area is equivocal. Accordingly, the\u0000Nordre Strømfjord shear zone is not an example of modern-style plate\u0000tectonics in the Paleoproterozoic or of very low thermal gradients and\u0000extreme pressure conditions in general.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46988300","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}

{"title":"Elasticity of mixtures and implications for piezobarometry of mixed-phase inclusions","authors":"Ross J. Angel, M. Mazzucchelli, K. Musiyachenko, F. Nestola, M. Alvaro","doi":"10.5194/ejm-35-461-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-461-2023","url":null,"abstract":"Abstract. Elastic thermobarometry (or piezobarometry) is the process of determining\u0000the P (pressure) and T (temperature) of entrapment of inclusions from their pressure, stress or strain\u0000measured when their host mineral is at room conditions. The methods and\u0000software used for piezobarometry are currently restricted to inclusions\u0000consisting of single phases. In this contribution we describe the theory of\u0000the elasticity of mixtures of different phases and combine it with the\u0000existing isotropic analysis of the elastic interactions between single-phase\u0000inclusions and their hosts to calculate the inclusion pressures of\u0000mixed-phase inclusions. The analysis shows that the reliability of\u0000calculated entrapment conditions for mixed-phase inclusions, including those\u0000containing fluid plus minerals, depends in a complex way upon the contrasts\u0000between the elastic properties of the host and the phases in the inclusion.\u0000The methods to calculate the entrapment conditions of mixed-phase inclusions\u0000have been incorporated into the EosFit7c program (version 7.6) that is available as\u0000freeware from http://www.rossangel.net.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"1 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41355338","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}

{"title":"Mineralogy and mineral chemistry of detrital platinum-group minerals and gold particles from the Elbe, Germany","authors":"M. Junge, S. Goldmann, H. Wotruba","doi":"10.5194/ejm-35-439-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-439-2023","url":null,"abstract":"Abstract. In heavy mineral concentrates of the Elbe, gold and\u0000platinum-group minerals (PGMs) are observed. Two fractions (> 63\u0000and < 63 µm) of the concentrate are analyzed by\u0000reflected-light microscopy, scanning electron microscopy with automated\u0000mineralogy software and electron microprobe analysis (EPMA). Other heavy\u0000minerals are cassiterite, ferberite, monazite, uraninite,\u0000columbite–tantalite, magnetite, zircon and cinnabar. Scanning electron\u0000microscopy determined the modal abundance of PGMs, gold and the other heavy\u0000minerals. The PGMs are mainly Os–Ir–Ru–(Pt) alloys, Pt–Fe alloys, sperrylite\u0000and rustenburgite. Compositional variation of PGMs and gold was analyzed by\u0000EPMA. This showed that Pt–Fe alloys are (1) native platinum (> 80 atom %), (2) ferroan Pt (20 atom % to 50 atom % Fe), (3) isoferroplatinum (2.64 to 3.04 apfu of sum PGE, platinum-group\u0000element), (4) tetraferroplatinum group with Ni + Cu + Fe ≈ 50 atom %, and (5)\u0000γ(Pt,Fe) with sum PGE > 3.04 apfu. The Os–Ir–Ru–(Pt)\u0000alloys show large compositional variations. Platinum and Fe enrichment is\u0000typically observed for Ir-rich Os–Ir–Ru alloys. Gold particles often show\u0000compositional zoning of Ag-rich cores and Ag-poor rims due to selective\u0000leaching of Ag. Similarly, Hg-rich rims of gold particles are analyzed.\u0000These are interpreted as the results of in situ amalgamation due to mobilization of\u0000Hg from the associated cinnabar particles. The size and shape of the gold\u0000particles generally argue for short transportation distances. Similarly,\u0000almost euhedral sperrylite and Pt–Fe alloys suggest a source region close to\u0000the sampling site. However, roundish Os–Ir–Ru–(Pt) alloys presumably have\u0000experienced longer transportation in the river. Gabbroic dikes of the\u0000Lusatia block contain sperrylite and gold particles, which can be the source\u0000for these particles found in the concentrate. The composition of the\u0000Os–Ir–Ru–(Pt) alloys is similar to previous studies on the Vestřev\u0000placer in Czech Republic. Both locations are within the drainage area of the\u0000Elbe and can therefore be the source of the PGM and gold particles in\u0000the concentrate.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48121856","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}

{"title":"Nomenclature of the triphylite group of minerals","authors":"L. Lyalina, E. Selivanova, F. Hatert","doi":"10.5194/ejm-35-427-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-427-2023","url":null,"abstract":"Abstract. In this paper we present a Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC)-accepted scheme for the\u0000classification and nomenclature of the triphylite group of minerals. The\u0000general formula of those minerals is M1M2TO4, where M1 and M2 refer to\u0000cations in an octahedral coordination: M1 = □, Na, Li; M2 = Mn2+,\u0000Fe2+, Mg, Fe3+, Mn3+, and T to tetrahedrally coordinated\u0000P5+ cations. The group contains the Li-bearing phosphates triphylite\u0000[LiFe2+(PO4)] and lithiophilite [LiMn2+(PO4)] and their\u0000oxidation products heterosite [Fe3+(PO4)] and purpurite\u0000[Mn3+(PO4)], as well as the Na-bearing phosphates natrophilite\u0000[NaMn2+(PO4)] and karenwebberite [NaFe2+(PO4)]. The\u0000Li–Mg-bearing phosphate simferite has been redefined as LiMg(PO4).\u0000Ferrisicklerite and sicklerite correspond to intermediate phases in the\u0000triphylite–heterosite and lithiophilite–purpurite solid solutions;\u0000consequently, according to the CNMNC dominant-constituent rule, they are\u0000discredited. A new mineral oxidation sequence is defined, which considers\u0000the different oxidation capacity of iron and manganese, and therefore\u0000replaces the traditional Quensel–Mason sequence. The formula calculation\u0000procedure for Li-bearing species, based on electron microprobe analyses and\u0000single-crystal X-ray diffraction data, is also described.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45699777","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}

{"title":"Multistage fluorite mineralization in the southern Black Forest, Germany: evidence from rare earth element (REE) geochemistry","authors":"Robin Hintzen, W. Werner, M. Hauck, R. Klemd, L. Fischer","doi":"10.5194/ejm-35-403-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-403-2023","url":null,"abstract":"Abstract. The Black Forest hosts a wide range of hydrothermal\u0000mineralization, including fluorite–barite vein deposits. In a detailed\u0000investigation of the Finstergrund and Tannenboden deposits in the Wieden\u0000mining district (southern Black Forest), the diversity, geochemical evolution\u0000and relative chronology of multistage fluorite precipitation is tracked on\u0000the basis of rare earth element (REE) geochemistry, geologic field relationships and crystal\u0000zoning. Geochemical discrimination and mathematical λ coefficients\u0000suggest a total of seven fluorite REE groups, at least three distinguishable\u0000post-Variscan fluid mobilization events and independent formation histories\u0000for the deposits despite their spatial proximity. Fluorite vein\u0000mineralization at the Finstergrund deposit evolved over three fluid\u0000generations, was derived from gneissic source aquifers and comprises five\u0000distinct fluorite REE groups: the first fluid generation is characterized by\u0000fluorite precipitation above 200 ∘C (“group III”), below 200 ∘C (“group I”) and after fractional crystallization (“group IV”);\u0000the second generation comprises remobilized fluorite (“group II”); and the\u0000third generation revealed fluorite precipitation by meteoric water mixing\u0000(“group V”). Fluorite vein formation at the Tannenboden deposit is\u0000associated with two distinct fluorite REE patterns derived from the same\u0000fluid generation: fluorite precipitation above 200 ∘C (“group\u0000VII”) and after cooling below 200 ∘C (“group VI”). Its fluid\u0000source aquifer lithology best matches migmatites contrary to previous models\u0000that suggest either gneissic or granitic aquifer rocks for fluorite vein\u0000precipitation in the Black Forest. The decoupled formation history between\u0000the deposits is tectonically controlled as suggested by a new genetic model\u0000for the Wieden mining district. The model argues for a change in the local\u0000fluid percolation network and the termination of hydrothermal activity at\u0000the Tannenboden deposit after the first fluid mobilization event. The geochemical evolution of multistage fluorite mineralization, as\u0000exemplified by the Tannenboden and Finstergrund deposits in combination with\u0000other fluorite mineralizations in the Black Forest, provides unique insights\u0000into the lithospheric origin and precipitation behaviour of fluorite by\u0000various fluid–rock interaction processes occurring in large hydrothermal\u0000systems. The local diversity of REE patterns emphasizes the need for\u0000detailed investigations of individual hydrothermal vein deposits.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41426744","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}

{"title":"IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 73","authors":"Ferdinando Bosi, Frédéric Hatert, Marco Pasero, Stuart J. Mills","doi":"10.5194/ejm-35-397-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-397-2023","url":null,"abstract":"","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135335911","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}

{"title":"Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U–Th) ∕ He geochronological analysis","authors":"K. Marques, T. Allard, C. Gautheron, B. Baptiste, R. Pinna‐Jamme, G. Morin, L. Delbes, P. Vidal‐Torrado","doi":"10.5194/ejm-35-383-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-383-2023","url":null,"abstract":"Abstract. Interpreting the ages of supergene mineralogical phases in\u0000laterite is complex because they consist of polycrystalline mixtures of\u0000different phases at the microscopic scale that could be crystalized at\u0000different epochs. Among the geochronometers, the (U-Th)/He method on\u0000hematite and goethite is more often used, but ages can be difficult to interpret\u0000due to phases mixing. To resolve this issue, this study proposes a\u0000methodology for performing detailed mineralogical analysis of hematite and\u0000goethite single grains prior to their dating using the (U-Th)/He method.\u0000Strictly non-destructive mineralogy of single grains is not achievable by\u0000classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams\u0000of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing).\u0000Therefore, we performed X-ray diffraction patterns of single grains using\u0000high-flux X-ray beams from both a rotating anode (XRD_rotat)\u0000laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on\u0000XRD_rotat only. For this purpose, two samples from the\u0000pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba\u0000region, Minas Gerais State, Brazil) were chosen because they presented a\u0000usual heterogeneity. Rietveld refinements of the XRD patterns obtained from\u0000both XRD_rotat and XRD_synch yielded similar\u0000results for the weight percentage ratio of the main phases and mean coherent domain\u0000sizes and less similar results for Al substitution rates, thus validating the\u0000XRD_rotat approach. No beam damage was observed when\u0000increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the\u0000mineralogy of ferruginous duricrusts by XRD_rotat with a\u0000short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex\u0000grains also provided meaningful ages: they revealed two evolution phases of\u0000the ferruginous duricrust, which occurred at or before the Oligocene for\u0000the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the\u0000previous model for the development of pisolites. The mineralogy of single\u0000grains selected for dating is helpful for discussing the crystallization\u0000ages, and the high-flux XRD approach may be applied to other supergene\u0000mineral parageneses used for absolute dating.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43306824","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}