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Occurrences of slawsonite in rocks of the teschenite association in the Podbeskydi Piedmont area (Czech Republic) and their petrological significance

Dalibor Matysek and Jakub Jirasek
Occurrences of slawsonite in rocks of the teschenite association in the Podbeskydi Piedmont area (Czech Republic) and their petrological significance
The Canadian Mineralogist (September 2016) 54 (5): 1129-1146

Abstract

Slawsonite is an extremely scarce natural member of the Feldspar Group, occurring in less than 10 known localities worldwide. We report three new slawsonite occurrences (in Certak, Krmelin, and Repiste) in rocks of the Cretaceous teschenite association in the Czech Republic. At Certak, a tabular sill of "teschenite" (in fact analcime syenite, based on its mineral composition) is one of the most alkaline examples of the teschenite association rocks. It shows differentiation to a coarser-grained core enriched in amphiboles, with diffuse transition to the outer zones. Rare thin leucocratic "aplite" dikes contain slawsonite, celsian, microcline, natrolite, prehnite, analcime, and thomsonite-Ca. Slawsonite forms aggregates exhibiting symplectite-like microstructures up to 2 mm long and is associated with euhedral zoned celsian micrograins up to 100 mu m in size. Wavelength dispersive X-ray analyses indicate that the chemical composition of slawsonite ranges from Sl (sub 90.4) Cn (sub 3.4) An (sub 1.7) Ab (sub 3.1) Or (sub 1.4) to Sl (sub 60.3) Cn (sub 8.7) An (sub 6.9) Ab (sub 18.3) Or (sub 5.8) ; the composition of celsian ranges from Cn (sub 95.8) An (sub 0.4) Ab (sub 1.0) Or (sub 2.3) Sl (sub 0.5) to Cn (sub 70.1) An (sub 0.5) Ab (sub 2.2) Or (sub 6.3) Sl (sub 20.9) ; and the Na-rich microcline exhibits a composition of Or (sub 58.3) An (sub 2.8) Ab (sub 29.4) Cn (sub 6.4) Sl (sub 3.1) Slawsonite from Krmelin and Repiste occurs in a similar geological setting, as aggregates up to 0.3 mm in size that are confined to leucocratic dikes at the endo-contacts of teschenite sills or lava pods. We suggest that slawsonite forms pseudomorphs after nepheline or possibly after plagioclase. Whole-rock geochemistry shows that local teschenites have an affinity for alkali basaltoid rocks typical of MORBs, but are significantly enriched in incompatible elements such as Rb, Ba, Th, U, Ta, Nb, and Sr. With regard to the obvious presence of autometamorphic hydrothermal alteration, we propose that bodies of teschenite association rocks should not be described as dikes; instead, a model of lava pods should be applied.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 54
Serial Issue: 5
Title: Occurrences of slawsonite in rocks of the teschenite association in the Podbeskydi Piedmont area (Czech Republic) and their petrological significance
Affiliation: Technical University of Ostrava, Faculty of Mining and Geology, Ostrava, Czech Republic
Pages: 1129-1146
Published: 201609
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 72
Accession Number: 2017-080350
Categories: Mineralogy of silicatesIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, sketch map
N49°40'00" - N49°55'00", E18°00'00" - E22°22'60"
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201742
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