The origin of intermediate and evolved lavas in the Marquesas archipelago: an example from Nuku Hiva island (French Polynesia) |
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| Institution: | 1. Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland;2. Faculty of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland;3. Instituto Dom Luiz, University of Beira Interior, Rua Marques d''Avila e Boloma, 6201-001 Covilhã, Portugal;4. Department of Earth Sciences, Science Labs, Durham University, Elvet Hill, Durham DH1 3LE, United Kingdom;5. Department of Geosciences and Natural Resource Management, University of Copenhagen, Rolighedsvej 23, 1958 Frederiksberg C, Denmark;1. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia;2. Institut des Sciences de la Terre (ISTerre) Universite J. Fourier-CNRS Maison des Goscience, Grenoble Alpes CS 40700 38058 GRENOBLE Cedex 9;3. Moscow State University, Leninskie Gory GSP-1, Moscow, 119991, Russia;4. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;1. Johannes Gutenberg-Universität Mainz, Institut für Geowissenschaften, Becherweg 21, 55099 Mainz, Germany;2. University of Belgrade, Faculty of Mining and Geology, Dju?ina 7, 11000 Belgrade, Serbia;3. Institute of Geodynamics, Romanian Academy, Jean-Louis Calderon 19-21, Bucharest 020032, Romania;1. Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS UMR 7154, 1 rue Jussieu, 75238 Paris, France;2. Institut Universitaire de France, Paris, France;3. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA;4. Department of Geology, University of Maryland, 237 Regents Drive, College Park, MD 20742, USA;5. Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195-1310, USA;1. Department of Earth and Environment, Florida International University, Miami, FL 33199, USA;2. ENVIRON, Los Angeles, CA 90017, USA;3. Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;4. Departamento de Geología y Geofísica, Universidad de Chile, Santiago, Chile;5. SERNAGEOMIN, Puerto Varas, Chile |
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| Abstract: | The Nuku Hiva Pliocene island (Marquesas, French Polynesia) is composed of a large half-collapsed tholeiitic shield volcano (the Tekao edifice), the caldera of which is filled up by the younger Taiohae volcano. The latter edifice is characterised by a complex magmatic association including minor mafic lavas (olivine tholeiites, alkali basalts and basanites), abundant intermediate lavas (hawaiites with subsidiary mugearites, both covering 47% of the surface of the volcano) and lesser amount of evolved lavas (K-rich and Na-rich trachytes and minor benmoreites, covering 25% of the edifice). Most intermediate and evolved Taiohae lavas are amphibole-rich and crystallised under high oxygen fugacities. The mafic Taiohae lavas originated from lower degree of melting of mantle sources more enriched than that of the shield volcano tholeiites. We show that closed-system fractional crystallisation of the Taiohae basaltic magmas can account for the origin of Taiohae hawaiites and mugearites, provided that separation of substantial amount of amphibole and/or apatite occurred during this process. Similarly, fractionation of benmoreitic magmas involving large amounts of amphibole and mica may account for the genesis of K-rich and Na-rich trachytes, respectively. However, fractional crystallisation cannot account for the derivation of benmoreitic magmas from mugearitic ones: since, this process fails to explain the abrupt increase in K2O from the latter to the former. In addition, the isotopic signature of trachytes and benmoreites is clearly distinct (more EM II-rich) from that of Taiohae basalts, hawaiites and mugearites. Three hypotheses could account for the genesis of benmoreitic magmas: assimilation of oceanic material with a strong EM II signature, differentiation of non-sampled mafic magmas derived from a mantle source having a EM II-rich signature and partial melting at depth of mafic material with a strong EM II signature. The oxidised character of Nuku Hiva lavas, uncommon in oceanic island settings, suggests interaction with water and/or the contribution of an oxidised (altered?) source material to their genesis. |
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