Trace element distribution among rock-forming minerals in Black Hills migmatites, South Dakota; a case for solid-state equilibrium

University of Missouri-Columbia, Department of Geological Sciences, Columbia, MO, United States

Proterozoic migmatites in the Black Hills, South Dakota, were examined to determine if partitioning of trace elements hosted by rock-forming minerals between melanosomes and leucosomes preserves residue-melt equilibrium that was presumably established during partial melting of pelitic lithologies. Granitic leucosomes in the Black Hills, as is often the case elsewhere, have positive Eu anomalies, are highly enriched in Sr and Ba, and are depleted in Rb and Cs relative to granites derived by partial melting of metapelites. Distributions of these trace elements between melanosomes and leucosomes cannot be simulated using mineral-melt distribution coefficients. A metamorphic reaction-progress method is used to demonstrate that the distributions approach mineral-mineral equilibrium rather than mineral-melt equilibrium. Application of published diffusion data for the relevant elements in feldspars shows that solid-state equilibrium is unlikely to have been established during subsolidus cooling. Instead, it is suggested that partial melts maintained chemical equilibrium with melanosomes during crystallization that lead to the migmatites.

This record provided courtesy of AGI/GeoRef.

This article has been cited by other articles:

				S. Bhadra, S. Das, and A. Bhattacharya Shear Zone-hosted Migmatites (Eastern India): the Role of Dynamic Melting in the Generation of REE-depleted Felsic Melts, and Implications for Disequilibrium Melting J. Petrology, March 1, 2007; 48(3): 435 - 457. [Abstract] [Full Text] [PDF]

				P. I. Nabelek, T. C. Labotka, T. Helms, and M. Wilke Fluid-mediated polymetamorphism related to Proterozoic collision of Archean Wyoming and Superior provinces in the Black Hills, South Dakota American Mineralogist, October 1, 2006; 91(10): 1473 - 1487. [Abstract] [Full Text] [PDF]

				N. HARRIS, A. McMILLAN, M. HOLNESS, R. UKEN, M. WATKEYS, N. ROGERS, and A. FALLICK Melt Generation and Fluid Flow in the Thermal Aureole of the Bushveld Complex J. Petrology, June 1, 2003; 44(6): 1031 - 1054. [Abstract] [Full Text] [PDF]

				T. E. Johnson, T.E. Johnson, N.F.C. Hudson, and G.T.R. Droop Evidence for a genetic granite-migmatite link in the Dalradian of NE Scotland Journal of the Geological Society, May 1, 2003; 160(3): 447 - 457. [Abstract] [Full Text] [PDF]

				L. M. Kriegsman and A. I. Nystrom Melt segregation rates in migmatites: review and critique of common approaches Geological Society, London, Special Publications, January 1, 2003; 220(1): 203 - 212. [Abstract] [PDF]

				A. I. Nystrom and L. M. Kriegsman Prograde and retrograde reactions, garnet zoning patterns, and accessory phase behaviour in SW Finland migmatites, with implications for geochronology Geological Society, London, Special Publications, January 1, 2003; 220(1): 213 - 230. [Abstract] [PDF]

				M. Wilke, P. I. Nabelek, and M. D. Glascock B and Li in Proterozoic metapelites from the Black Hills, U.S.A.: Implications for the origin of leucogranitic magmas American Mineralogist, April 1, 2002; 87(4): 491 - 500. [Abstract] [Full Text] [PDF]

				G. S. SOLAR and M. BROWN Petrogenesis of Migmatites in Maine, USA: Possible Source of Peraluminous Leucogranite in Plutons? J. Petrology, April 1, 2001; 42(4): 789 - 823. [Abstract] [Full Text] [PDF]

				P. I. Nabelek, M. Sirbescu, and M. Liu Petrogenesis and tectonic context of the Harney Peak Granite, Black Hills, South Dakota Rocky Mountain Geology, November 1, 1999; 34(2): 165 - 181. [Abstract] [Full Text] [PDF]