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Water concentrations and hydrogen isotope compositions of alkaline basalt hosted clinopyroxene megacrysts and amphibole clinopyroxenites: the role of structural hydroxyl groups and molecular water

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Tartalom: http://real.mtak.hu/29457/
Archívum: MTA Könyvtár
Gyűjtemény: Status = Submitted



Type = Article
Cím:
Water concentrations and hydrogen isotope compositions of alkaline basalt hosted clinopyroxene megacrysts and amphibole clinopyroxenites: the role of structural hydroxyl groups and molecular water
Létrehozó:
Kovács, István János
Demény, Attila
Czuppon, György
Lécuyer, Christophe
Fourel, Francois
Xia, Qunke
Liu, Jia
Pintér, Zsanett
Király, Edit
Török, Kálmán
Szabó, Ábel
Deloule, Etienne
Falus, György
Fancsik, Tamás
Zajacz, Zoltán
Sándorné Kovács, Judit
Dátum:
2015
Téma:
QD05 Crystallography / kristálytan
QD06 Mineralogy / ásványtan
QE06 Petrology. Petrography / kőzettan, petrográfia
Tartalmi leírás:
The aim of this study was to determine both 'water' contents (as OH- and H2O) and ?D values of several clinopyroxene samples from alkaline basalts. These parameters were first obtained from five clinopyroxene samples using both the classical 'off-line' vacuum
extraction technique and the 'on-line' high-temperature pyrolysis technique. Blanks measured with the 'on-line' gas extraction techniques were low enough to prevent any
contamination by atmospheric water vapour. The comparison of data has revealed that the 'on-line' procedure is more effective for the extraction of 'water' from clinopyroxenes
and, consequently, this 'on-line' technique was applied to ten additional clinopyroxene samples. Sample ?D values cover a similar range from -95? to -45? (VSMOW) regardless the studied locations, whereas the total 'water' content varies from 1150 to 2570 ppm. The structural hydroxyl content of clinopyroxene samples measured by micro-FTIR spectrometry varies from ~0 to 476 ppm expressed in molecular water equivalent. There is a weak negative correlation between the total water concentrations determined by mass spectrometry and FTIR, thus indicating that considerable proportion of the 'water' may be present in (nano)-inclusions. It is observed, however, that the structural hydroxyl concentration - apart from linopyroxenes separated from amphibole clinopyroxenite xenoliths - correlates positively with the ?D values of clinopyroxene megacrysts for each locality, indicating
that structurally bond hydrogen in clinopyroxenes may have ?D values higher than molecular water in inclusions. This implies that that there may be a significant hydrogen isotope fractionation for structural hydroxyl during crystallization of clinopyroxene while for molecular water there may be no or only negligible isotope fractionation.
Típus:
Article
NonPeerReviewed
Formátum:
text
Azonosító:
Kovács, István János and Demény, Attila and Czuppon, György and Lécuyer, Christophe and Fourel, Francois and Xia, Qunke and Liu, Jia and Pintér, Zsanett and Király, Edit and Török, Kálmán and Szabó, Ábel and Deloule, Etienne and Falus, György and Fancsik, Tamás and Zajacz, Zoltán and Sándorné Kovács, Judit (2015) Water concentrations and hydrogen isotope compositions of alkaline basalt hosted clinopyroxene megacrysts and amphibole clinopyroxenites: the role of structural hydroxyl groups and molecular water. Contributions to Mineralogy and Petrology. ISSN 1432-0967 (Submitted)
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