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Alkalic magmas generated by partial melting of garnet pyroxenite

Marc M. Hirschmann, Tetsu Kogiso, Michael B. Baker and Edward M. Stolper
Alkalic magmas generated by partial melting of garnet pyroxenite
Geology (Boulder) (June 2003) 31 (6): 481-484


Many oceanic-island basalts (OIBs) with isotopic signatures of recycled crustal components are silica poor and strongly nepheline (ne) normative and therefore unlike the silicic liquids generated from partial melting of recycled mid-oceanic-ridge basalt (MORB). High-pressure partial-melting experiments on a garnet pyroxenite (MIX1G) at 2.0 and 2.5 GPa produce strongly ne-normative and silica-poor partial melts. The MIX1G solidus is located below 1350 and 1400 degrees C at 2 and 2.5 GPa, respectively, slightly cooler than the solidus of dry peridotite. Chemographic analysis suggests that natural garnet pyroxenite compositions straddle a thermal divide. Whereas partial melts of compositions on the silica-excess side of the divide (such as recycled MORB) are silica saturated, those from silica-deficient garnet pyroxenites can be alkalic and have similarities to low-silica OIB. Although the experimental partial melts are too rich in Al (sub 2) O (sub 3) to be parental to highly undersaturated OIB suites, higher-pressure (4-5 GPa) partial melting of garnet pyroxenite is expected to yield more appropriate parental liquids for OIB lavas. Silica-deficient garnet pyroxenite, which may originate by mixing of MORB with peridotite, or by recycling of other mafic lithologies, represents a plausible source of OIB that may resolve the apparent contradiction of strongly alkalic composition with isotopic ratios characteristic of a recycled component.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 31
Serial Issue: 6
Title: Alkalic magmas generated by partial melting of garnet pyroxenite
Affiliation: University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN, United States
Pages: 481-484
Published: 200306
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 31
Accession Number: 2003-045523
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: California Institute of Technology, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200314
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