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Markers of the pyroxenite contribution in the major-element compositions of oceanic basalts: Review of the experimental constraints

Lambart, Sarah and Laporte, Didier and Schiano, Pierre (2013) Markers of the pyroxenite contribution in the major-element compositions of oceanic basalts: Review of the experimental constraints. Lithos, 160 . pp. 14-36. ISSN 0024-4937.

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Based on previous and new results on partial melting experiments of pyroxenites at high pressure, we attempt to identify the major element signature of pyroxenite partial melts and to evaluate to what extent this signature can be transmitted to the basalts erupted at oceanic islands and mid-ocean ridges. Although peridotite is the dominant source lithology in the Earth's upper mantle, the ubiquity of pyroxenites in mantle xenoliths and in ultramafic massifs, and the isotopic and trace elements variability of oceanic basalts suggest that these lithologies could significantly contribute to the generation of basaltic magmas. The question is how and to what degree the melting of pyroxenites can impact the major-element composition of oceanic basalts. The review of experimental phase equilibria of pyroxenites shows that the thermal divide, defined by the aluminous pyroxene plane, separates silica-excess pyroxenites (SE pyroxenites) on the right side and silica-deficient pyroxenites (SD pyroxenites) on the left side. It therefore controls the melting phase relations of pyroxenites at high pressure but, the pressure at which the thermal divide becomes effective, depends on the bulk composition; partial melt compositions of pyroxenites are strongly influenced by non-CMAS elements (especially FeO, TiO_2, Na_2O and K_2O) and show a progressive transition from the liquids derived from the most silica-deficient compositions to those derived from the most silica-excess compositions. Another important aspect for the identification of source lithology is that, at identical pressure and temperature conditions, many pyroxenites produce melts that are quite similar to peridotite-derived melts, making the determination of the presence of pyroxenite in the source regions of oceanic basalts difficult; only pyroxenites able to produce melts with low SiO_2 and high FeO contents can be identified on the basis of the major-element compositions of basalts. In the case of oceanic island basalts, high CaO/Al_2O_3 ratios can also reveal the presence of pyroxenite in the source-regions. Experimental and thermodynamical observations also suggest that the interactions between pyroxenite-derived melts and host peridotites play a crucial role in the genesis of oceanic basalts by generating a wide range of pyroxenites in the upper mantle: partial melting of such secondary pyroxenites is able to reproduce the features of primitive basalts, especially their high MgO contents, and to impart, at least in some cases, the major-element signature of the original pyroxenite melt to the oceanic basalts. Finally, we highlight that the fact the very silica depleted compositions (SiO_2 < 42 wt.%) and high TiO_2 contents of some ocean island basalts seem to require the contribution of fluids (CO_2 or H_2O) through melting of either carbonated lithologies (peridotite or pyroxenite) or amphibole-rich veins.

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Laporte, Didier0000-0003-1965-2351
Additional Information:© 2012 Elsevier B.V. Received 27 August 2012. Accepted 17 November 2012. Available online 24 November 2012. We are grateful to Andrew Kerr for inviting us to write this review article. We thank Jacques Kornprobst, Emeritus Professor at Université Blaise Pascal, Clermont-Ferrand, for providing the two pyroxenites from Beni Bousera used in this study. Special thanks are also due to the following persons: Jean-Louis Fruquière and Frank Pointud for manufacturing the piston–cylinder assemblages and for maintenance operations, and Jean-Luc Devidal and Chi Ma for technical assistance with the electron microprobes. This study has benefited from discussions with Paul Asimow, Mike Baker, Edward Stolper, Marion Le Voyer and Christophe Brosson. This is Laboratory of Excellence ClerVolc contribution no. 46. This work was also supported by the program DyETI of the Institut National des Sciences de l'Univers (INSU-CNRS), by the Agence Nationale de la Recherche ‘MIME’ grant (ANR-07-BLAN-0130-01 to A. Provost), and by the National Science Foundation grant EAR-9528594. We also thank Claude Herzberg and an anonymous reviewer for their constructive reviews.
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Institut National des Sciences de l'Univers (INSU-CNRS)-DyETI programUNSPECIFIED
Agence Nationale de la Recherche (ANR)ANR-07-BLAN-0130-01
Subject Keywords:Experimental petrology; Pyroxenite; Thermal divide; Oceanic basalts; Partial melting; Melt–peridotite interactions
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Laboratory of Excellence ClerVolc contribution46
Record Number:CaltechAUTHORS:20130412-075955074
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Official Citation:Sarah Lambart, Didier Laporte, Pierre Schiano, Markers of the pyroxenite contribution in the major-element compositions of oceanic basalts: Review of the experimental constraints, Lithos, Volumes 160–161, February 2013, Pages 14-36, ISSN 0024-4937, 10.1016/j.lithos.2012.11.018. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37895
Deposited By: Ruth Sustaita
Deposited On:12 Apr 2013 15:32
Last Modified:09 Mar 2020 13:18

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