Stable (H, O, C) and noble-gas (He and Ar) isotopic compositions from calcite and fluorite in the Speewah Dome, Kimberley Region, Western Australia: implications for the conditions of crystallization and evidence for the influence of crustal-mantle fluid mixing

Gy Czuppon, R. R. Ramsay, I. Özgenc, A. Demény, L. G. Gwalani, K. Rogers, A. Eves, L. Papp, L. Palcsu, M. Berkesi, P. J. Downes

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

In this study, the C-O-isotopic data from calcite at Yungul and Wilmott (Speewah. Western-Australia) are integrated with microthermometry, H2O-, CO2-content and H-He-Ar-isotopic data from fluid inclusions in genetically related calcite and fluorite to map the origin and crystallization paths of the fluids. In addition to the hydrogen isotopic compositions of fluid inclusions in fluorite, oxygen isotopic compositions were also determined by cavity ring-down spectroscopy. The geochemical data suggest mixing of a CO2-dominated mantle fluid and a H2O-domintated crustal brine. The fluid produced by this mixing is characterized by radiogenic (crustal-like) 3He/4He ratios, crustal-like δD values, relatively high salinity (19 − 24wt.% NaCl eq.), moderate homogenization temperatures (150 − 450 °C) and mantle-like CO2/3He ratios. Moreover, the large isotopic and elemental variations found in calcite indicate that its formation was accompanied by an extensive degassing (open system) leading to a decrease in δD and an increase in the CO2/3He values relative to the starting fluid composition. This degassing is consistent with the fluidal- and breccia-like texture of calcite observed in the field. In contrast, the fluorite which has coarse-grained banded to vughy textures formed in a passive aqueous system. Apparently the fluid that formed the fluorite has the same origin as the calcite, but the higher water content and the more radiogenic 3He/4He ratios reflect a greater involvement of crustal fluids. The historical description of the calcite-fluorite system in the Speewah area as “carbonatite” is now considered inappropriate because there is no evidence that crystallization is dominated by magmatic processes.

Original languageEnglish
Pages (from-to)759-775
Number of pages17
JournalMineralogy and Petrology
Volume108
Issue number6
DOIs
Publication statusPublished - Nov 15 2014

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Noble Gases
Fluorspar
Calcium Carbonate
noble gas
Domes
fluorite
domes
Crystallization
calcite
dome
rare gases
Earth mantle
isotopic composition
crystallization
mantle
Fluids
fluid
fluids
Chemical analysis
degassing

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

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Stable (H, O, C) and noble-gas (He and Ar) isotopic compositions from calcite and fluorite in the Speewah Dome, Kimberley Region, Western Australia : implications for the conditions of crystallization and evidence for the influence of crustal-mantle fluid mixing. / Czuppon, Gy; Ramsay, R. R.; Özgenc, I.; Demény, A.; Gwalani, L. G.; Rogers, K.; Eves, A.; Papp, L.; Palcsu, L.; Berkesi, M.; Downes, P. J.

In: Mineralogy and Petrology, Vol. 108, No. 6, 15.11.2014, p. 759-775.

Research output: Contribution to journalArticle

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