Temporal evolution and geochemical variability of the South Pacific superplume activity

Abstract

International audienceWe are presenting a new set of K/Ar ages and geochemical analyses obtained on deep-sea samples dredged in 1999 on several seamounts of the Cook–Austral volcanic chains in the Pacific Ocean. The new geochemical results, together with published data on island samples, allow us to reveal a time evolution of the mantle source composition as well as an increase in geochemical variability of the superplume responsible for the regional South Pacific Superswell. Three identified volcanic stages of 58–40, 33–20 and 20–0 Ma are identified with signatures of mantle reservoir composition varying from close to C to N-MORB-types and C/HIMU-type, respectively. Using a geodynamic reconstruction for the most recent volcanic period, from 20 Ma to present, three hotspot tracks are needed to explain the several volcanic episodes observed within the limited geographical area of the central part of the Cook–Austral chains. At the scale of a single volcano, different magmatic phases can also be identified with different ages and geochemical signatures, emphasizing the importance of structural control, either crustal or lithospheric, in the location of the magmatic outputs. These observations, taken together, are in good agreement with a model where each hotspot could sample a small volume of the large very heterogeneous plume responsible for the regional South Pacific Superswell

Progressive island colonization and ancient origin of Hawaiian Metrosideros (Myrtaceae)

“…However, some ambiguity remains because the molecular data provide insufficient resolution to clearly distinguish a monophyletic Hawaiian group from the closest sister group in the Marquesas or to establish that Kaua'i was colonized from the Marquesas and not vice versa. In addition, shifting the calibration age of node A to some of the oldest Austral Island ages (Bonneville et al 2006) would require colonization of now submerged islands in the Hawaiian chain by Metrosideros more than 13 Myr ago. More plausibly, the location of the Marquesas between the Hawaiian Islands and the probable source populations for the Hawaiian-Marquesan clade in central and southern French Polynesia makes a northward direction of colonization probable.…”

“…(e) Rate calibration along proposed dispersal route We used the ages of volcanic islands to date nodes of the phylogeny within the Hawaiian Islands, and along the most likely dispersal route from New Zealand (Clague 1996;Craig et al 2001;Price & Clague 2002;Bonneville et al 2006). The ages of islands along the most likely dispersal route allow an independent test of a calibration based only on ages within the Hawaiian Islands.…”

Origin of hotspots in the South Pacific: Recent advances in seismological and geochemical models

“…Each narrow plume may sample volumes with different geochemical characteristics, thereby resulting in different geochemical signatures (e.g., trace element and isotopic composition) at different hotspots in the South Pacific (Zindler and Hart, 1986;Bonneville et al, 2006). We speculate that all distinct geochemical components, including EM1 and EM2, may be present in the superplume although the depth of origin and formation processes for the EM1 and EM2 lavas are yet to be determined.…”

“…This area subsides less rapidly away from the East Pacific Rise than predicted by any thermal subsidence model of oceanic lithosphere (McNutt and Fischer, 1987 (Bonneville et al, 2006) Dalrymple et al (1975), Duncan and McDougall (1976), Bellon et al (1980), Turner and Jarrard (1982), Maury et al (1994), and Bonneville et al (2006). can be attributed to the dynamic support of the ascending plume in the upper mantle beneath the hotspots (Adam et al, 2010). The superswell extends between latitudes 10°N and 30°S and longitudes 130°W and 160°W on a seafloor displaying ages between 30 and 115 Ma (Adam and Bonneville, 2005).…”

“…Age determinations had been restricted to subaerial lavas in 1990s (except for Macdonald Seamount), but the presence of Atiu trend was confirmed by the discovery of the Arago Seamount dated at 0.2 Ma; therefore, this seamount must be near the present position of the hotspot forming the Atiu trend (or Arago trend; Bonneville et al, 2002). Bonneville et al (2006) further suggested that the northern and southern Austral Islands may represent distinct trends because of the geographical offset of the chains between Raivavae and Neilson Bank and the distinct geochemical features of the trends in the northern and southern Austral Islands. Possible interpretations of the complicated emplacement of these island chains will be discussed later.…”