Insights Into the Origin of the Longest-lived Hotspot in the Pacific: Clues from the Tuvalus

Insights Into the Origin of the Longest-lived Hotspot in the Pacific: Clues from the Tuvalus Anthony A.P. Koppers1, Jasper G. Konter2, Matthew G. Jackson3 1College of Earth, Ocean and Atmospheric Sciences, Oregon State University 2Dept. Geological Sciences, University of Texas at El Paso 3Dept. Earth Science, University of California, Santa Barbara Several prominent, long-lived volcanic chains stand out as bathymetric features on the Pacific plate. Several of these hotspot chains are long-lived, and thought to be fed by buoyantly upwelling mantle plumes. In the North Pacific, the Hawaiian hotspot has been continuously erupting for 85 Ma, and exhibits a sharp bend at ~50-47 Ma. Similarly, the Louisville hotspot, located in the South Pacific, exhibits volcanic activity going back to 76 Ma, but unlike Hawaii, the Louisville hotspot exhibits a more gradual change in orientation at ~50 Ma. The disparity between the traces of these two prominent hotspots in the Pacific, and the suggested plume source motion for Hawaii, as well as the observation that their respective hotspots traces are subducted at a relatively young age, prompted a thorough investigation of the Pacific hotpots in search of third, longer-lived hotspot that can be compared to Hawaii and Louisville. We suggest that the hotspot anchored to Rurutu, located in the Austral Islands, is the longest-lived (>100 Ma and up to 120 Ma at least) in the Pacific and will provide a third long-lived hotspot trace that will both inform upon and extend current plate motion models in the Pacific. Plate motion models predict that the ~50 Ma bend for the Rurutu hotspot is located where the Tuvalu Islands and Samoan Seamounts intersect, and the modeled trace of the Rurutu hotspot continues up through the Tuvalu and Gilbert Islands. Additionally, the Rurutu hotspot has a radiogenic Pb-isotopic (HIMU) signature, compared to the radiogenic Sr-isotopic signature of Samoa. Therefore, the unique geochemical signature of the Rurutu hotspot, together with its predicted hotspot track, make it relatively straightforward to test whether Tuvalu Islands represent the Rurutu hotspot right before its Hawaii-Emperor Bend. Initial radiogenic isotopic data obtained on deeply-dredged samples from the Tuvalu Islands showed that the islands belong to the HIMU geochemical taxonomy, which is consistent with an origin at the Rurutu hotspot. Here we present preliminary data on lavas from the 35-day dredging expedition aboard the R/V Roger Revelle (Expedition RR1310 from July 22 to August 25, 2013, starting in Guam and ending in Fiji). In total more than 25 separate seamounts and atolls were dredged in the Tuvalu Islands, and relatively fresh, dateable (by Ar-Ar) lavas were recovered from most dredges. Sample compositions range from olivine (+/- clinopyroxene)-rich basalts to plagioclase, amphibole and/or biotite-bearing trachytes/phonolites that were analyzed on-board by LIBS (Laser Induced Breakdown Spectroscopy).