Carbonic fluids in ultrahigh-temperature metamorphism: Evidence from Raman spectroscopic study of fluid inclusions in granulites from the Napier complex, East Antarctica

T. Tsunogae, M. Santosh, J. Dubessy, Y. Osanai, M. Owada, T. Hokada, T. Toyoshima

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)

Abstract

We report the first quantitative compositional data on fluid inclusions in ultrahigh-temperature (UHT) granulites from the Napier Complex of Enderby Land, East Antarctica. Fluid inclusions in various high-grade minerals such as garnet, orthopyroxene and sapphirine from three UHT localities in the Amundsen Bay area were studied in terms of petrography and microthermometry as well as laser Raman spectroscopy. Measured melting temperatures of inclusions from all the three localities indicate that the trapped fluid phase is dominantly carbonic. Raman analyses confirmed a near pure CO2 composition with only minor dilutants such as N2 (<6.0 mol%), CH4 (<0.3 mol%), and H2O(<0.1 mol%). CH4-bearing fluid associated with sapphirine granulites suggests low oxygen fugacity (f O2) conditions for the rocks, whereas CH4 was not detected from fluid inclusions in magnetite-bearing high-f O2 garnet granulite. The range of CO2 isochores computed from density measurements in fluid inclusions from the granulites pass through the peak P-T conditions of the Napier metamorphism (T = 1050-1150 °C, P = 9-11kbar) indicating synmetamorphic nature of the fluids. Inclusions in garnet from Bunt Island coexist with carbonate minerals (magnesite) and graphite along with dense CO2-rich fluid, indicating probable derivation from deep-seated primary magmatic sources. The ubiquitous association of carbonic fluids in the UHT mineral assemblages suggests CO2 influx during extreme crustal metamorphism of the Napier Complex. The carbonic fluid probably played an important role in transporting heat from mantle or mantle-derived magmas and in stabilizing the dry mineral assemblages.

Original languageEnglish
Pages (from-to)317-332
Number of pages16
JournalGeological Society Special Publication
Volume308
DOIs
Publication statusPublished - 2008

All Science Journal Classification (ASJC) codes

  • Water Science and Technology
  • Ocean Engineering
  • Geology

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