Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

Minerals

卷:8

CaileyB. Condit¹  KellyC. Curtis²  KevinH. Mahan²  Andreas Möller³ 

[1] Department of Earth, Environmental and Planetary Sciences, Rice University, Houston 77005, TX, USA;

[2] Department of Geological Sciences, University of Colorado, Boulder 80309, CO, USA;

[3] Department of Geology, The University of Kansas, Lawrence 66045, KS, USA;

关键词: metasomatism;    albitization;    geochronology;    trace element geochemistry;    monazite;    zircon;    SW Montana;   

DOI  :  10.3390/min8050187

来源: DOAJ

【 摘 要 】

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.

【 授权许可】

Unknown