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Experimental derivation of nepheline syenite and phonolite liquids by partial melting of upper mantle peridotites

Laporte, Didier and Lambart, Sarah and Schiano, Pierre and Ottolini, Luisa (2014) Experimental derivation of nepheline syenite and phonolite liquids by partial melting of upper mantle peridotites. Earth and Planetary Science Letters, 404 . pp. 319-331. ISSN 0012-821X. doi:10.1016/j.epsl.2014.08.002.

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Piston-cylinder experiments were performed to characterize the composition of liquids formed at very low degrees of melting of two fertile lherzolite compositions with 430 ppm and 910 ppm K_2O at 1 and 1.3 GPa. We used the microdike technique (Laporte et al., 2004) to extract the liquid phase from the partially molten peridotite, allowing us to analyze liquid compositions at degrees of melting F down to 0.9%. At 1.3 GPa, the liquid is in equilibrium with olivine + orthopyroxene + clinopyroxene + spinel in all the experiments; at 1 GPa, plagioclase is present in addition to these four mineral phases up to about 5% of melting (T≈1240°C). Important variations of liquid compositions are observed with decreasing temperature, including strong increases in SiO_2, Na_2O, K_2O, and Al_2O_3 concentrations, and decreases in MgO, FeO, and CaO concentrations. The most extreme liquid compositions are phonolites with 57% SiO_2, 20–22% Al_2O_3, Na_2O + K_2O up to 14%, and concentrations of MgO, FeO, and CaO as low as 2–3%. Reversal experiments confirm that low-degree melts of a fertile lherzolite have phonolitic compositions, and pMELTS calculations show that the amount of phonolite liquid generated at 1.2 GPa increases from 0.3% in a source with 100 ppm K_2O to 3% in a source with 2000 ppm K_2O. The enrichment in silica and alkalis with decreasing melt fraction is coupled with an increase of the degree of melt polymerization, which has important consequences for the partitioning of minor and trace elements. Thus Ti^(4+) in our experiments and, by analogy with Ti^(4+), other highly charged cations, and rare earth elements become less incompatible near the peridotite solidus. Our study brings a strong support to the hypothesis that phonolitic lavas or their plutonic equivalents (nepheline syenites) may be produced directly by partial melting of upper mantle rock-types at moderate pressures (1–1.5 GPa), especially where large domains of the subcontinental lithospheric mantle has been enriched in potassium by metasomatism. The circulation of low-degree partial melts of peridotites into the upper mantle may be responsible for a special kind of metasomatism characterized by Si- and alkali-enrichment. When they are unable to escape by porous flow, low-degree melts will ultimately be trapped inside neighboring olivine grains and give rise to the silica- and alkali-rich glass inclusions found in peridotite xenoliths.

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Laporte, Didier0000-0003-1965-2351
Additional Information:© 2014 Elsevier B.V. Received 24 April 2014. Received in revised form 30 July 2014. Accepted 4 August 2014. Available online 27 August 2014. Editor:J. Brodholt. Jean-Luc Devidal is thanked for his efficient analytical assistance with the electron microprobe and for the preparation of synthetic gels. We are grateful to Mhammed Benbakkar and Jean-Marc Hénot for analytical assistance, to Christian Pin for discus-sions on the occurrence of silica-undersaturated felsic rocks in orogenic lherzolites, and to Pierre Condamine and Etienne Médard for sharing their unpublished manuscript. The constant support of Karine David to DL is gratefully acknowledged. We would like to thank the anonymous reviewers for their constructive comments and John Brodholt for editing our manuscript. This work was initiated within the framework of the Research Training Network EUROMELT (HPRN-CT-2002-00211) of the European Community’s Human Potential Program. The experimental and analytical costs were covered by financial supports from the program SYSTER of the Institut National des Sciences de l’Univers (INSU-CNRS) and from the Agence Nationale de la Recherche (ELECTROLITH project, contract no. ANR-2010-BLAN-621). SL’s work was supported by the National Science Foundation(EAR-1019886). The experimental facilities in Clermont-Ferrand benefited from the support of the French Government Laboratory of Excellence initiative n◦ANR-10-LABX-0006, the Région Auvergne and the European Regional Development Fund. This is Laboratory of Excellence ClerVolc contribution number 111.
Funding AgencyGrant Number
European Community’s Human Potential ProgramHPRN-CT-2002-00211
Institut National des Sciences de l’Univers (INSU)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS) (France)UNSPECIFIED
Agence Nationale de la Recherche (ANR)ANR-2010-BLAN-621
Agence Nationale de la Recherche (ANR)ANR-10-LABX-0006
Région AuvergneUNSPECIFIED
European Regional Development FundUNSPECIFIED
Subject Keywords:upper mantle; lherzolite; partial melting; phonolite; mantle metasomatism; potassium
Record Number:CaltechAUTHORS:20141120-135612882
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Official Citation:Didier Laporte, Sarah Lambart, Pierre Schiano, Luisa Ottolini, Experimental derivation of nepheline syenite and phonolite liquids by partial melting of upper mantle peridotites, Earth and Planetary Science Letters, Volume 404, 15 October 2014, Pages 319-331, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52013
Deposited By: Ruth Sustaita
Deposited On:21 Nov 2014 17:43
Last Modified:10 Nov 2021 19:19

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