Origin of fluorapatite-monazite assemblages in a metamorphosed, sillimanite-bearing pegmatoid, Reinbolt Hills, East Antarctica

Martin A. Ziemann, Hans-Jürgen Förster, Daniel E. Harlov, Dirk Frei

Publikation: Bidrag til tidsskriftArtikelForskningpeer review

31 Citationer (Scopus)

Abstrakt

Thermobarometrical and mineral-chemical investigations by electron microprobe and LA-ICP-MS on a sillimanite-bearing pegmatoid from the Reinbolt Hills provide important constraints on the P-T-X-age relations of part of East Antarctica during Pan-African tectonism. U-Th-total Pb ages of monazite imply that the pegmatoid of originally Grenvillan age (zircon U-Pb age of ca. 900 Ma) underwent a major, late Pan-African (Cambrian) regional, granulite-facies metamorphism between 500 and 550 Ma. Most of the monazite formed during this event, as result of apatite metasomatism owing to infiltration of high-grade metamorphic fluids. Apatite-biotite and other mineral thermobarometers define the peak metamorphic temperatures and pressures with 850-950 °C and 0.8-1.0 GPa. The F-Cl-OH relations in apatite and biotite, the chemistry of fluid inclusions and the presence of K-feldspar microveins suggest that the metasomatising fluid was a CO 2-bearing, diluted KCl brine. The pegmatoid is the first record of monazite-(Ce) formed from fluorapatite that is rich in U (up to 2.6 wt% UO 2) and possesses Th/U ratios < 1 (0.09 on average). These chemical signatures are direct reflection of the U and Th concentration patterns in the parental fluorapatite.

OriginalsprogEngelsk
Sider (fra-til)567-580
Antal sider14
TidsskriftEuropean Journal of Mineralogy
Vol/bind17
Udgave nummer4
DOI
StatusUdgivet - 2005

Programområde

  • Programområde 5: Natur og klima

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