Crystal chemistry and evolution of tourmaline in tourmalinites from Zlatá Idka, Slovakia

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
P. Bačík, D. Ozdín, P. Uher, M. Chovan, Al□Mg, AlOMg, Mg, FeCaAl
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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.
斯洛伐克zlat Idka地区电气石中电气石的晶体化学及演化
电气石产于斯洛伐克东部卡尔帕提亚斯西部ZlatáIdka村附近的Gemeric单元早古生代变质岩中。用电子探针分析电气石的组成,包括广泛的电气石种类。ZlatáIdka电气石中的电气石在成分上是可变的,主要取代Mg–Fe2+与常见的scholl–dravite成分及其氟和氧主要对应物——氟scholl、氟dravite、氧scholl和氧dravite一致。电气石的一部分以萤石和镁铝石成分的形式富含Ca。组成的一个子集具有每个化学式单位(apfu)大于0.25个原子的Ti,并且对应于假设的“镁质杜罗镁石”,即杜罗镁岩的Mg占主导地位的类似物。此外,一些电气石是X位空位,并被归类为辉橄榄岩。电气石的晶体化学是复杂的,并受到几种交换机制的影响,包括Mg(Fe)-1,Al□(Mg,Fe)-1 Na–1,AlO(Mg和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和TiMg(Al)-2取代。一般来说,所有样品中的电气石通常具有振荡分区的通风核心和斜方边缘(Tur I)。然而,在ZLT-4和ZLT-6样品中,一些晶体具有次生Mg为主和Ca富集的过度生长(Tur II),部分取代了Tur I。电气石很可能是由区域或接触交代过程产生的,可能是由于二叠纪Poproč花岗岩体的侵入。电气石的起源可能是由晚期岩浆到早期岩浆后富含B、F的流体从花岗岩侵入邻近变质岩的结果。电气石结晶及其化学成分受变质母岩和花岗岩侵入体的控制;Tur I的富镁岩芯很可能在成分上与变质橄榄岩宿主岩有关,而边缘中后来的钠橄榄岩-钠橄榄岩成分表明是由于侵入引发的流体流动引起的。电气石区域的显著变化和振荡意味着一种动态的、不稳定的流体状态。晚期富钙Tur II可能是与寄主岩石矿物蚀变相关的后续交代过程的结果。
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来源期刊
Journal of Geosciences
Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-MINERALOGY
CiteScore
2.30
自引率
7.10%
发文量
15
审稿时长
>12 weeks
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.
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