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Occurrence and chemical composition of barian feldspars in a jadeitite from the Itoigawa-Omi District in the Renge high-P/T-type metamorphic belt, Japan

T. Morishita
Occurrence and chemical composition of barian feldspars in a jadeitite from the Itoigawa-Omi District in the Renge high-P/T-type metamorphic belt, Japan
Mineralogical Magazine (February 2005) 69 (1): 39-51

Abstract

Coexisting Ba-rich (Cn (sub 56-59) O (sub 40-42) Ab (sub 2) An (sub 0-1) ) and Ba-poor (Cn (sub 7-15) Or (sub 83-92) Ab (sub 1-3) An (sub 0-1) ) feldspars were found in a jadeitite collected from the Itoigawa-Ohmi district in the Renge high-P/T-type metamorphic belt, Japan. There is an apparent compositional gap in these barian feldspars at Cn (sub 15-56) in the ternary system BaAl (sub 2) Si (sub 2) O (sub 8) -KAlSi (sub 3) O (sub 8) -NaAlSi (sub 3) O (sub 8) . Barian feldspars occur as interstitial phases between subhedral to euhedral jadeite and prehnite, and sometimes cut a jadeite crystal. The occurrence of barian feldspars combined with the texture and mineral assemblages of the host jadeitite suggest that barian feldspars were formed from residual fluids after the formation of jadeite and prehnite from primary aqueous fluids at low-T conditions (<350 degrees C) and pressure of approximately 0.6 GPa. The Ba content in the residual fluids would increase locally during the formation of jadeite because Ba is incompatible with clinopyroxene. This study supports the suggestion that Ba-rich minerals are not uncommon in jadeitites and albitites/metasomatized rocks that occur as tectonic blocks in serpentinite-matrix melanges. Barium is an important minor element in metasomatizing fluids related to the formation of jadeitites and might have been derived from subducted oceanic crust at the beginning of the subduction.


ISSN: 0026-461X
EISSN: 1471-8022
Coden: MNLMBB
Serial Title: Mineralogical Magazine
Serial Volume: 69
Serial Issue: 1
Title: Occurrence and chemical composition of barian feldspars in a jadeitite from the Itoigawa-Omi District in the Renge high-P/T-type metamorphic belt, Japan
Author(s): Morishita, T.
Affiliation: Kanazawa University, Graduate School of Natural Science and Technology, Kanazawa, Japan
Pages: 39-51
Published: 200502
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 63
Accession Number: 2005-041364
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch map
N37°00'00" - N37°00'00", E137°00'00" - E137°00'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200525
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