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Solid solution between potassic alkali amphiboles from the silica-rich Kvaloya Lamproite, West Troms basement complex, Northern Norway

Kare Kullerud, Dmitry Zozulya, Muriel Erambert and Erling J. K. Ravna
Solid solution between potassic alkali amphiboles from the silica-rich Kvaloya Lamproite, West Troms basement complex, Northern Norway
European Journal of Mineralogy (February 2014) 25 (6): 935-945

Abstract

Alkali amphibole of rare compositions occurs as a rock-forming mineral in a high-Si phlogopite lamproite from Kvaloya, northern Norway. The amphibole typically occurs as small grains forming irregular and rosette-shaped aggregates in a matrix dominated by Fe-rich K-feldspar and quartz. Amphibole shows compositions ranging between the three limiting compositions: A: (super A,B) (K (sub 1.01) Na (sub 1.99) ) (super C) (Na (sub 0.26) Mg (sub 1.58) Mn (sub 0.03) Fe (super 2+) (sub 0.91) Fe (super 3+) (sub 1.6 ) Ti (sub 0.47) [] (sub 0.13) ) (super T) Si (sub 8) O (sub 22) (super W) [F (sub 0.97) O (sub 1.03) ] B: (super A,B) (KNa (sub 2) ) (super C) (Na (sub 0.04) Mg (sub 1.04) Mn (sub 0.22) Fe (super 2+) (sub 0.65) Fe (super 3+) (sub 2.07) Ti (sub 0.25 ) [] (sub 0.7) ) (super T) Si (sub 8) O (sub 22) (super W) [F (sub 0.68) Cl (sub 0.01) O (sub 0.13) (OH) (sub 1.18) ] C: (super A,B) (K (sub 0.9) N (sub 2.1) ) (super C) (Na (sub 0.04) Mg (sub 3.54) Mn (sub 0.02) Fe (super 2+) (sub 0.28) Fe (super 3+) (sub 1.04) T i (sub 0.03) [] (sub 0.02) (super T) Si (sub 8) O (sub 22) (super W) [F (sub 1.34) O (sub 0.06) (OH) (sub 0.6) ] Composition C shows significant content of fluoro-potassic-magnesio-arfvedsonite, while composition A is a Fe (super 2+) , Fe (super 3+) and (super C) Na rich variety of potassic-obertiite. Composition B is characterized by an exceptional high value of (super C) []. It is emphasized that the presence of (super C) [] and (super C) Na in amphibole needs to be confirmed by other methods. The relationship between (super W) O (super 2-) , (super C) [],Ti (super 4+) and Fe (super 3+) of amphibole can be expressed by the following exchange operators, choosing potassic-magnesio-arfvedsonite [KNa (sub 2) (Mg (sub 4) Fe (super 3+) )Si (sub 8) O (sub 22) (OH) (sub 2) ] as the additive component: Ti (super 4+) Mg (super 2+) (sub -1) H (super +) (sub -2) Fe (super 3+) Mg (super 2+) (sub -1) H (super +) (sub -1) Ti (super 4+) []Mg (super 2+) (sub -2) Fe (super 3+) (sub 2) []Mg (super 2+) (sub -3) The two first exchange operators result in deprotonation of OH, while the two others result in the formation of vacancies on the C sites. The presence of amphibole both in the lamproite and in the adjacent fenitized granite suggests that the mineral formed during reactions between rock and fluids derived from the volatile-rich lamproite magma. Possibly, amphibole core (composition A and B), formed in equilibrium with the fluid phase during crystallization of the melt, while amphibole rim (composition C) formed during subsequent mineral-fluid reactions. Presence of hematite in the lamproite matrix in addition to oxo-amphibole indicates that the rock formed during highly oxidizing conditions.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 25
Serial Issue: 6
Title: Solid solution between potassic alkali amphiboles from the silica-rich Kvaloya Lamproite, West Troms basement complex, Northern Norway
Affiliation: University of Tromso, Department of Geology, Tromso, Norway
Pages: 935-945
Published: 201402
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 29
Accession Number: 2014-028553
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N69°37'00" - N69°37'00", E18°33'00" - E18°33'00"
Secondary Affiliation: Russian Academy of Sciences, Geological Institute, RUS, Russian FederationUniversity of Oslo, NOR, Norway
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201418
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