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Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization.
- Source :
-
Minerals (2075-163X) . May2018, Vol. 8 Issue 5, p187-N.PAG. 1p. - Publication Year :
- 2018
-
Abstract
- We present coupled textural observations and trace element and geochronological data from metasomatic monazite and zircon, to constrain the timing of high-grade Na-metasomatism (albitization) of an Archean orthogneiss in southwest Montana, USA. Field, mineral textures, and geochemical evidence indicate albitization occurred as a rind along the margin of a ~3.2 Ga granodioritic orthogneiss (Pl + Hbl + Kfs + Qz + Bt + Zrn) exposed in the Northern Madison range. The metasomatic product is a weakly deformed albitite (Ab + Bt + OAm + Zrn + Mnz + Ap + Rt). Orthoamphibole and biotite grew synkinematically with the regional foliation fabric, which developed during metamorphism that locally peaked at upper amphibolite-facies during the 1800–1710 Ma Big Sky orogeny. Metasomatism resulted in an increase in Na, a decrease in Ca, K, Ba, Fe, and Sr, a complete transformation of plagioclase and K-feldspar into albite, and loss of quartz. In situ geochronology on zoned monazite and zircon indicate growth by dissolution–precipitation in both phases at ~1750–1735 Ma. Trace element geochemistry of rim domains in these phases are best explained by dissolution–reprecipitation in equilibrium with Na-rich fluid. Together, these data temporally and mechanistically link metasomatism with high-grade tectonism and prograde metamorphism during the Big Sky orogeny. [ABSTRACT FROM AUTHOR]
- Subjects :
- *METASOMATISM
*GEOCHRONOMETRY
*MONAZITE
*AMPHIBOLITES
*ZIRCON
*GEOLOGICAL time scales
Subjects
Details
- Language :
- English
- ISSN :
- 2075163X
- Volume :
- 8
- Issue :
- 5
- Database :
- Academic Search Index
- Journal :
- Minerals (2075-163X)
- Publication Type :
- Academic Journal
- Accession number :
- 129822563
- Full Text :
- https://doi.org/10.3390/min8050187