The size of plume heterogeneities constrained by Marquesas isotopic stripes

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 13; no. 7; pp. np - n/a
• Main Authors: Chauvel, Catherine, Maury, René C., Blais, Sylvain, Lewin, Eric, Guillou, Hervé, Guille, Gérard, Rossi, Philippe, Gutscher, Marc-André
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.07.2012; John Wiley & Sons, Inc; AGU and the Geochemical Society
• Subjects: Archipelagoes; Domes; Earth Sciences; Environmental Sciences; Filaments; Geochemistry; Global Changes; Heterogeneity; Islands; isotopes; Mantle; Marquesas; Melting; ocean island; plume structure; Plumes; Polynesia; Sciences of the Universe; Trace elements; ISE, Pacific, French Polynesia, Marquesas Is., Ua Huka; ISE, Pacific, French Polynesia, Marquesas Is., Fatu Hiva; ISE, Pacific, French Polynesia, Marquesas Is; Polynesia; USA, Hawaii; Marquesas; ocean island; isotopes; plume structure
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2012GC004123

The scale and geometry of chemical and isotopic heterogeneities in the source of plumes have important scientific implications on the nature, composition and origin of plumes and on the dynamics of mantle mixing over time. Here, we address these issues through the study of Marquesas Islands, one of the Archipelagoes in Polynesia. We present new Sr, Nd, Pb, Hf isotopes as well as trace element data on lavas from several Marquesas Islands and demonstrate that this archipelago consists of two adjacent and distinct rows of islands with significantly different isotopic compositions. For the entire 5.5 Ma construction period, the northern islands, hereafter called the Ua Huka group, has had systematically higher 87Sr/86Sr and lower 206Pb/204Pb ratios than the southern Fatu Hiva group at any given 143Nd/144Nd value. The shape and curvature of mixing arrays preclude the ambient depleted MORB mantle as one of the mixing end‐members. We believe therefore that the entire isotopic heterogeneity originates in the plume itself. We suggest that the two Marquesas isotopic stripes originate from partial melting of two adjacent filaments contained in small plumes or “plumelets” that came from a large dome structure located deep in the mantle under Polynesia. Low‐degree partial melting under Marquesas and other “weak” Polynesian hot spot chains (Pitcairn‐Gambier, Austral‐Cook, Society) sample small areas of the dome and preserve source heterogeneities. In contrast, more productive hot spots build up large islands such as Big Island in Hawaii or Réunion Island, and the higher degrees of melting blur the isotopic variability of the plume source. Key Points Isotopic stripes in the Marquesas chain Size of isotopic filaments in a plume Relationship between size of island and isotopic range