Effect of water on the composition of partial melts of greenstone and amphibolite

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Authors:Beard, James S.; Lofgren, Gary E.
Author Affiliations:Primary:
NASA, Johnson Space Cent., Houston, TX, United States
Volume Title:Science
Source:Science, 244(4901), p.195-197. Publisher: American Association for the Advancement of Science, Washington, DC, United States. ISSN: 0036-8075
Publication Date:1989
Note:In English. 16 refs.; illus. incl. 1 table
Summary:Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich anhydrous restites, and have compositions like island arc tonalites. In contrast, water- saturated melting at water P of 3 kbar yields strongly peraluminous, low-iron melts that coexist with an amphibole- bearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of P in the crust of island arcs is a plausible mechanism for the petrogenesis of island arc tonalite, whereas water-saturated melting at P of 3 kbar and above is not. [Authors' abstract] [K.F.]
Subjects:Amphibolites; Closed systems; Dehydration; Diorites; Experimental studies; Greenstone; Hydration; Igneous rocks; Island arcs; Meta-andesite; Metabasalt; Metaigneous rocks; Metamorphic rocks; Metavolcanic rocks; Partial melting; Plutonic rocks; Saturation; Schists; Tonalite; Water
Abstract Numbers:90M/0432
Record ID:1989039066
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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