P. Bačík, D. Ozdín, P. Uher, M. Chovan, Al□Mg, AlOMg, Mg, FeCaAl
{"title":"Crystal chemistry and evolution of tourmaline in tourmalinites from Zlatá Idka, Slovakia","authors":"P. Bačík, D. Ozdín, P. Uher, M. Chovan, Al□Mg, AlOMg, Mg, FeCaAl","doi":"10.3190/jgeosci.350","DOIUrl":null,"url":null,"abstract":"Tourmalinites occur in early-Paleozoic metamorphic rocks of the Gemeric Unit near Zlatá Idka village, Western Car-pathians, eastern Slovakia. Tourmaline compositions, analyzed with the electron microprobe, include a wide range of tourmaline species. Tourmaline in tourmalinites from Zlatá Idka is compositionally variable, with the dominant substitution Mg–Fe 2+ consistent with prevalent schorl–dravite compositions and their fluor-and oxy-dominant counterparts – fluor-schorl, fluor-dravite, oxy-schorl and oxy-dravite. Portions of tourmaline are enriched in Ca in the form of the fluor-uvite and magnesio-lucchesiite components. A subset of the compositions has Ti > 0.25 atoms per formula unit ( apfu ) and corresponds to the hypothetical “magnesio-dutrowite”, Mg-dominant analogue of dutrowite. In addition, some of the tourmalines are X -site vacant and classified as foitite. The crystal chemistry of tourmaline is complex and influenced by several exchange mechanisms, including Mg(Fe) –1 , Al□(Mg,Fe) –1 Na –1 , AlO(Mg,Fe) –1 (OH) –1 (Mg,Fe)CaAl –1 Na –1 , MgCaOAl –1 □ –1 (OH) –1 , Ti 0.5 O(Fe,Mg) –0.5 (OH) –1 and TiMg(Al) –2 substitutions. In general, tourmalines in all samples usually have oscillatory-zoned dravitic cores and schorlitic rims (Tur I). However, in ZLT-4 and ZLT-6 samples, some crystals have secondary Mg-dominant and Ca-enriched overgrowths (Tur II), partially replacing Tur I. Tourmalinites were most likely produced by regional or contact metasomatic processes, likely due to the intrusion of the Permian Poproč granitic massif. Origin of tourmalinites likely results from the flow of late-magmatic to early post-magmatic B,F-rich fluids from the granite intrusion into adjacent metamorphic rocks. The tourmaline crystallization and its resulting chemical composition were controlled by both the metapelitic host rock and the granitic intrusion; the Mg-rich cores of the Tur I are most likely compositionally related to the metapelitic host rock, whereas later schorlitic to foititic compositions in rims suggest origin due to the intrusion-triggered fluid flow. The significant changes and oscillations of tourmaline zon - ing imply a dynamic, unstable fluid regime. The late Ca-rich Tur II could result from subsequent metasomatic processes associated with the alteration of host-rock minerals.","PeriodicalId":15957,"journal":{"name":"Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":1.1000,"publicationDate":"2022-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Geosciences","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.3190/jgeosci.350","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 1
Abstract
Tourmalinites occur in early-Paleozoic metamorphic rocks of the Gemeric Unit near Zlatá Idka village, Western Car-pathians, eastern Slovakia. Tourmaline compositions, analyzed with the electron microprobe, include a wide range of tourmaline species. Tourmaline in tourmalinites from Zlatá Idka is compositionally variable, with the dominant substitution Mg–Fe 2+ consistent with prevalent schorl–dravite compositions and their fluor-and oxy-dominant counterparts – fluor-schorl, fluor-dravite, oxy-schorl and oxy-dravite. Portions of tourmaline are enriched in Ca in the form of the fluor-uvite and magnesio-lucchesiite components. A subset of the compositions has Ti > 0.25 atoms per formula unit ( apfu ) and corresponds to the hypothetical “magnesio-dutrowite”, Mg-dominant analogue of dutrowite. In addition, some of the tourmalines are X -site vacant and classified as foitite. The crystal chemistry of tourmaline is complex and influenced by several exchange mechanisms, including Mg(Fe) –1 , Al□(Mg,Fe) –1 Na –1 , AlO(Mg,Fe) –1 (OH) –1 (Mg,Fe)CaAl –1 Na –1 , MgCaOAl –1 □ –1 (OH) –1 , Ti 0.5 O(Fe,Mg) –0.5 (OH) –1 and TiMg(Al) –2 substitutions. In general, tourmalines in all samples usually have oscillatory-zoned dravitic cores and schorlitic rims (Tur I). However, in ZLT-4 and ZLT-6 samples, some crystals have secondary Mg-dominant and Ca-enriched overgrowths (Tur II), partially replacing Tur I. Tourmalinites were most likely produced by regional or contact metasomatic processes, likely due to the intrusion of the Permian Poproč granitic massif. Origin of tourmalinites likely results from the flow of late-magmatic to early post-magmatic B,F-rich fluids from the granite intrusion into adjacent metamorphic rocks. The tourmaline crystallization and its resulting chemical composition were controlled by both the metapelitic host rock and the granitic intrusion; the Mg-rich cores of the Tur I are most likely compositionally related to the metapelitic host rock, whereas later schorlitic to foititic compositions in rims suggest origin due to the intrusion-triggered fluid flow. The significant changes and oscillations of tourmaline zon - ing imply a dynamic, unstable fluid regime. The late Ca-rich Tur II could result from subsequent metasomatic processes associated with the alteration of host-rock minerals.
期刊介绍:
The Journal of Geosciences is an international peer-reviewed journal published by the Czech Geological Society with support from the Czech Geological Survey. It accepts high-quality original research or review papers dealing with all aspects of the nature and origin of igneous and metamorphic rocks. The Journal focuses, mainly but not exclusively, on:
-Process-oriented regional studies of igneous and metamorphic complexes-
Research in structural geology and tectonics-
Igneous and metamorphic petrology-
Mineral chemistry and mineralogy-
Major- and trace-element geochemistry, isotope geochemistry-
Dating igneous activity and metamorphic events-
Experimental petrology and mineralogy-
Theoretical models of igneous and metamorphic processes-
Mineralizing processes and mineral deposits.
All the papers are written in English, even though they may be accompanied by an additional Czech abstract. Each contribution is a subject to peer review by at least two independent reviewers, typically at least one from abroad. The Journal appears 2 to 4 times a year. Formally it is divided in annual volumes, each of them including 4 issues.