Partial melting of two amphibolites; contrasting experimental results under fluid-absent conditions

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Authors:Rushmer, Tracy
Author Affiliations:Primary:
ETH-Zürich, Dep. Erdwissenschaften, Zurich, Switzerland
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 107(1), p.41-59. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1991
Note:In English. 2 p. refs.; illus. incl. 4 tables, 11 anals.
Summary:A large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase. As a consequence, H2O-undersaturated or fluid-absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events. In an attempt to determine the systematics of melting under fluid-absent conditions, a series of piston-cylinder experiments was conducted on two natural amphibolites: a meta-alkali basalt (ABA) with a total water content of approx 1 wt.% contained in hornblende, and a meta-island-arc tholeiite (IAT) which has approx 1-3 wt.% water in hornblende, cummingtonite and biotite. The experimentally determined melting ranges of the two amphibolites showed that the solidus T, and the T interval over which the amphibole was stable, were controlled by the amphibolites' different bulk compositions and their resulting metamorphic assemblages. The volume % of melt produced by melting of the two amphibolites was compared to amounts estimated by earlier workers, and were greater than estimated. As the water content of melt largely determines the vol.% of melt produced, independent measurements of the water- content of the glass formed during partial melting in the ABA were made by thermogravimetric analyses. The water content of the ABA glass is 2 wt.%, which is less than the assumed 'melt water' content used in previous modelling of fluid-absent anatexis in mafic lithologies. Consequently, more melt can be expected during fluid-absent partial melting of mafic lower crust, as was observed in the experiments. A fluid-absent melting model for mafic compositions is presented for P of 5, 8 and 10 kbar. [Author's abstract] [P.Br.]
Subjects:Amphibolites; Basalts; Chemical composition; Experimental studies; Igneous rocks; Melts; Metabasalt; Metaigneous rocks; Metamorphic rocks; Partial melting; Tholeiite; Volcanic rocks; Volume
Abstract Numbers:91M/4257
Record ID:1993021469
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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