Mineralogy of the Plio-Pleistocene potassic and ultrapotassic volcanic rocks from the Republic of Macedonia

Yanev, Yotzo and Boev, Blazo and Manetti, Piero and Ivanova, Rositsa and D’Orazio, Massimo and Innocenti, Fabrizio (2008) Mineralogy of the Plio-Pleistocene potassic and ultrapotassic volcanic rocks from the Republic of Macedonia. Geochemistry, Mineralogy and Petrology. pp. 35-67.

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Ultra- to high potassic volcanic rocks of Plio-Pleistocene age (3.24-1.47 Ma) crop out in the Vardar zone. On the basis of chemical composition, they are classified as phonotephrites to ultrapotassic shoshonites and latites, including also high-Mg latites. They contain pheno- and microphenocrysts of olivine, clinopyroxene, phlogopite, ± leucite. The groundmass consists of poikilitic Ba-Na sanidine and Ba-Ti phlogopite, ± Sr-rich oligoclase (up to 3 wt.% SrO), anorthoclase and Mg-bearing calcite, all enclosing microlites of clinopyroxene, phlogopite, Ti-magnetite, ± leucite. The olivine phenocrysts are zoned, forsterite-rich (up to Fo 93), and display a positive correlation between Fo component and NiO and negative one between the same component and MnO. The clinopyroxenes are diopside-augites, and some of them are rich in Al (up to 5.4 wt.% Al2O3), which correlates positively with Ti. On the other hand, Ti correlates negatively with Mg# and Si. The micas are essentially phlogopites rich in Ti (up to 12 wt.% TiO2). In some localities they are also highly enriched in Ba (up to 8.3 wt.% BaO) approaching to the Ti-kinoshitalite composition. Ba in micas correlates positively with Ti and Al, but negatively with K, Mg# as well as with Si. A positive correlation between Ba and Sr and negative one between Ba and Si/Al ratio is observed in both sanidine and plagioclase. The leucite microphenocrysts are sometimes replaced by Na-sanidine, zeolites (laumontite, phillipsite, etc.) and clays or by nepheline and amorphous nephelinic masses. The obtained mineralogical features of the Macedonian ultrapotassic rocks assign them to the Roman Province Type rocks.

Item Type: Article
Subjects: Natural sciences > Other natural sciences
Divisions: Faculty of Natural and Technical Sciences
Depositing User: Blazo Boev
Date Deposited: 20 Nov 2012 10:56
Last Modified: 10 Jun 2013 09:20
URI: http://eprints.ugd.edu.mk/id/eprint/1408

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