The Role of Halogens During Regional and Contact Metamorphism

Hammerli, Johannes; Rubenach, Michael J.

doi:10.1007/978-3-319-61667-4_10

Cited by 9 publications

(3 citation statements)

References 229 publications

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“…Complexes with halogens ( [69] and its references) and, to a lesser extent, CO 3 2− and PO 4 3− ligands [70], played a decisive role in the transfer of these elements. In our case, the main transfer agent was fluorine.…”

Section: Discussionmentioning

confidence: 99%

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

et al. 2018

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This article is devoted to the geology of titanium-rich varieties of the Petyayan-Vara rare-earth dolomitic carbonatites in Vuoriyarvi, Northwest Russia. Analogues of these varieties are present in many carbonatite complexes. The aim of this study was to investigate the behavior of high field strength elements during the late stages of carbonatite formation. We conducted a multilateral study of titanium-and niobium-bearing minerals, including a petrographic study, Raman spectroscopy, microprobe determination of chemical composition, and electron backscatter diffraction. Three TiO 2 -polymorphs (anatase, brookite and rutile) and three pyrochlore group members (hydroxycalcio-, fluorcalcio-, and kenoplumbopyrochlore) were found to coexist in the studied rocks. The formation of these minerals occurred in several stages. First, Nb-poor Ti-oxides were formed in the fluid-permeable zones. The overprinting of this assemblage by residual fluids led to the generation of Nb-rich brookite (the main niobium concentrator in the Petyayan-Vara) and minerals of the pyrochlore group. This process also caused niobium enrichment with of early generations of Ti oxides. Our results indicate abrupt changes in the physicochemical parameters at the late hydro (carbo) thermal stage of the carbonatite formation and high migration capacity of Ti and Nb under these conditions. The metasomatism was accompanied by the separation of these elements.

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Section: Discussionmentioning

confidence: 99%

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

et al. 2018

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“…Several criteria have been proposed for the identification of replaced evaporites in Precambrian successions (Warren, 2016). The criteria are based particularly on the chemistry of mineral phenocrysts that developed during metamorphism up to hundreds of millions of years after sedimentation (Moine et al 1981;Warren, 2016;Hammerli & Rubenach, 2018). The evidence is most convincing where there are multiple positive criteria.…”

Section: Criteriamentioning

confidence: 99%

Seawater signatures in the supracrustal Lewisian Complex, Scotland

2022

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Marble in the supracrustal rocks of the Lewisian Complex, Tiree, includes chlorine-bearing amphiboles, chlorine-rich apatite, sulphur-rich scapolite, albite and phlogopite, all of which are regarded as evidence for evaporites in other metamorphosed sequences. Titanite yields U–Pb ages of ∼1.6 Ga, i.e. late Laxfordian, which excludes a younger imprint of sodium metasomatism. Traces of anhydrite, and isotopically heavy pyrite, also indicate deposition from seawater. Elsewhere in the Hebrides, tourmaline in Lewisian Complex marbles may represent seafloor exhalative deposits. Combined, the evidence suggests Lewisian Complex supracrustal marbles formed in an evaporative environment, like other Palaeoproterozoic successions across the North Atlantic region.

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“…Chevychelov et al 2008;Aranovich and Safonov 2018), although some authors obtained discordant results (Siron et al 2018;Heckel et al 2020), possibly due to threshold effects in halogen concentration (Daigle 2015). The low abundance of halogens in silicates makes in situ analysis difficult as detection limits are often too high (Hammerli and Rubenach 2018). Bulk analyses may be carried out for F, Cl and Br (see Pagé et al (2018) for serpentinites) but point analyses are needed to constrain partitioning between minerals.…”

Section: Introductionmentioning

confidence: 99%

Crystal chemistry and partitioning of halogens in hydrous silicates

Figowy

Dubacq

D’Arco

2021

Contrib Mineral Petrol

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Understanding how halogens are distributed among usual hydrous silicates in the lithosphere is important to constrain their deep geochemical cycle and fluid-rock interactions in subduction zones. This article presents firstprinciples modelling of halogen (F -, Cl -, Br -) incorporation in hydrous silicates including mica, chlorite, serpentine, amphibole, epidote and carpholite. The approach allows studying the impact of crystal chemistry on halogen partitioning by quantification of the energetic cost of halogen incorporation in minerals. Calculations are carried out in large systems where halogens are in minor to trace concentrations. Estimations show that F-bearing defects must be separated at least 9 Å from one another to reproduce trace element behaviour, this value increasing to at least 10 Å for Cl and Br. Results highlight the competition between the effects of electrostatic interactions and steric hindrance for incorporation of halogens, where steric hindrance has greater importance for heavy halogens, in particular for Br. Interaction with alkalis is a major control for F incorporation, especially in mica. Other parameters such as octahedral site occupancy, Si/Al ratio of tetrahedral sites and the nature of alkalis in amphibole and mica (K or Na) appear to play subordinate roles. Partition coefficients have been estimated in mineral assemblages in an effort to be representative of subduction zone metamorphism. Results show that pargasite, biotite and lizardite are favoured hosts for all three halogens, followed by clinochlore, tremolite and carpholite. The energetic cost of incorporating halogens into dioctahedral phyllosilicates and epidote is comparatively higher, and partitioning is predicted as unfavourable to these minerals. Fractionation between halogens in subduction zones is predicted by the evolution of mineral assemblages and partition coefficients, a consequence of the influence of crystal chemistry over halogen incorporation in hydrous silicates.

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The Role of Halogens During Regional and Contact Metamorphism

Cited by 9 publications

References 229 publications

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

Seawater signatures in the supracrustal Lewisian Complex, Scotland

Crystal chemistry and partitioning of halogens in hydrous silicates

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