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Granite formation: Stepwise accumulation of melt or connected networks?

Published online by Cambridge University Press:  01 March 2009

Paul D. Bons
Affiliation:
Mineralogy and Geodynamics, Institute for Geosciences, Eberhard Karls University Tübingen, Wilhelmstr. 56, 72074 Tübingen, Germany Email: paul.bons@uni-tuebingen.de; becker@jkbecker.de
Jens K. Becker
Affiliation:
Mineralogy and Geodynamics, Institute for Geosciences, Eberhard Karls University Tübingen, Wilhelmstr. 56, 72074 Tübingen, Germany Email: paul.bons@uni-tuebingen.de; becker@jkbecker.de
Marlina A. Elburg
Affiliation:
Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium Email: Marlina.Elburg@UGent.be
Kristjan Urtson
Affiliation:
Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia Email: urtson@gi.ee
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Abstract

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Several authors have proposed that granitic melt accumulation and transport from the source region occurs in networks of connected melt-filled veins and dykes. These models envisage the smallest leucosomes as ‘rivulets’ that connect to feed larger dykes that form the ‘rivers’ through which magma ascends through the sub-solidus crust. This paper critically reviews this ‘rivulets-feeding-rivers’ model. It is argued that such melt-filled networks are unlikely to develop in nature, because melt flows and accumulates well before a fully connected network can be established. In the alternative stepwise accumulation model, flow and accumulation is transient in both space and time. Observations on migmatites at Port Navalo, France, that were used to support the existence of melt-filled networks are discussed and reinterpreted. In this interpretation, the structures in these migmatites are consistent with the collapse and draining of individual melt batches, supporting the stepwise accumulation model.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 2010