Geology and geochemistry of the Spuhler Peak Metamorphic Suite

Burger, H. Robert; Peck, William H.; Johnson, Kathleen E.; Tierney, Kara A.; Poulsen, Christopher J.; Cady, Pamela; Lowell, J. David; MacFarlane, W A; Sincock, M. Jennifer; Archuleta, LeAndra L.; Pufall, A.; Cox, Margaret

doi:10.1130/0-8137-2377-9.47

Cited by 4 publications

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“…It is possible that thin evaporite layers may have released sodium to increase salinity in the dewatering metamorphic fluids. In the nearby Tobacco Root Mountains ( Figure 1A), another package of metavolcaniclastic and metasedimentary rocks, the Spuhler Peak metamorphic suite, preserves similar fluid-related and metasomatic features to those observed in Bear Basin [82]. These rocks appear to record another locus of metasomatism and alteration within the Big Sky orogeny.…”

Section: Tectonic Significance Of Metasomatism and Regional Fluid Flowmentioning

confidence: 92%

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

et al. 2018

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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.

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Section: Tectonic Significance Of Metasomatism and Regional Fluid Flowmentioning

confidence: 92%