Melt segregation in the lower crust; how have experiments helped us?

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Authors:Rushmer, Tracy
Author Affiliations:Primary:
University of Vermont, Department of Geology, Burlington, VT, United States
Other:
U. S Geological Survey, United States
University of St. Andrews, United Kingdom
Volume Title:third Hutton symposium on the Origin of granites and related rocks
Volume Authors:Brown, M., editor; Candela, P. A.; Peck, D. L.; Stephens, W. E.; Walker, R. J.; Zen, E-an
Source:Special Paper - Geological Society of America, Vol.315, p.73-83; The third Hutton symposium on the Origin of granites and related rocks, College Park, MD, Aug. 27-Sept. 2, 1995, edited by M. Brown, P. A. Candela, D. L. Peck, W. E. Stephens, R. J. Walker and E-an Zen. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0072-1077. ISBN: 0-8137-2325-9
Publication Date:1996
Note:In English. 44 refs.Copubl. with R. Soc. of Edinburgh; illus., incl. 2 tables
Summary:Experiments performed on crustal rock cores under both hydrostatic conditions and during deformation have led to two conclusions. 1) The interfacial energy controlling melt distribution is anisotropic and, as a result, the textures deviate significantly from those predicted for ideal systems; planar solid-melt interfaces are developed in addition to triple junction melt pockets. The ideal dihedral angle model for melt distribution cannot be used as a constraint to predict melt migration in the lower crust. 2) The 'critical melt fraction' model, requiring viscous granitic melt to remain in the source until melt fractions reach >><[dollar]I> 25 vol.%, is not a reliable model for melt segregation, which is controlled by several variables, including the depth of melting, the type of reaction and the volume change associated with that reaction. Larger scale processes such as tectonic environment determine the rate at which the lower crust heats and deforms, thus the tectonic setting controls the melt fraction at which segregation takes place, in addition to the P and T of the potential melting reactions. Melt migration therefore can occur at a variety of different melt fractions depending on the tectonic environment; these results have significant implications for the predicted geochemistry of the magmas themselves. [R.A.H.]
Subjects:Anatexis; Controls; Crust; Deformation; Experimental studies; Geochemistry; Granites; Granitic composition; Igneous rocks; Lower crust; Melting; Melts; Partial melting; Plutonic rocks; Rheology; Strain; Stress; Evolution
Abstract Numbers:97M/905
Record ID:1997012338
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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