Introduction to the Rurutu Hotspot Trail

The island of Rurutu, French Polynesia, in the mid-Pacific ocean, presents the possibility of being the longest surviving hotspot trail. When current absolute plate motion models are applied to Rurutu, the hotspot traces back through modern day Samoa, the Tuvalu islands, Gilbert ridge, and into the N-S Wake area. In order to test the plate motion model, evidence for the long lived history of Rurutu is needed. Rurutu island contains a distinct 'HIMU' chemical signature (HIMU is defined by strong enrichments in radiogenic lead isotopes) which can be used to distinguish the hotspot from nearby Samoa (alternately showing an 'enriched mantle' signature high in radiogenic strontium isotopes). This is helpful as some seamounts in the Samoa region are much older than expected based on current plate motion models and they also contain the HIMU signature of Rurutu. Therefore, it is hypothesized that the Rurutu hotspot was active in the region currently occupied by Samoa around 40 to 70 million years ago. The Tuvalu islands are coral-rich atolls, which contain no exposed rock outcrops and therefore require dredging of the seamount's flanks in order to get samples of volcanic origin. This expedition aims to dredge 25-30 seamounts in the Tuvalu and Samoa regions in an attempt to map the history of the Rurutu hotspot. The major goals of the expedition are listed below.

A map of the western Pacific showing the modeled track of the Rurutu hotspot (blue) compared to the potential hotspot track of the Northern & Southern Wake seamount trails (red) that would have no active hotspot today (see red symbols). Hawaii-Emperor and Louisville hotspot tracks are shown for comparison. The region in the white-rimmed 'Fig. 2' box shows the area in which dredging will occur. The inset in the top right corner shows the 'hotspot highway' where hotspot trails from the Samoa, Rarotonga, Rurutu and Macdonald hotspots are overlain. The inset in bottom left corner shows the expected difference in the angle of the Hawaiian-Emperor bend for the Hawaiian, Rurutu and Louisville hotspots.
Scientific Goals

(1) Map out and trace the timing of the Rurutu bend using 40Ar/39Ar geochronology.
(2) Distinguish between the volcanoes of the Samoan and Rurutu hotspot tracks both chronologically and geochemically.
(3) Integrate the new age progression data into a new absolute plate motion (APM) model for the Pacific Plate.

Operational Plan

The five week cruise will depart from Guam on July 22nd and arrive in Fiji on August 25th in 2013, on the R/V Roger Revelle. The primary activities will be multibeam mapping and dredging of seamounts, with magnetic surveying while we are in transit to our research area and between the dredging of seamounts. The initial plan is to sample at least 20 seamounts of varying sizes and positions in the Tuvalu, Samoan and Tongan seas. Additional seamounts will be added or removed from the cruise track as time and weather permits.

Each seamount will first be mapped with the Revelle’s EM122 multibeam system to collect high-resolution maps that will help identify a suitable dredge site. As soon as a site is identified, the dredge will be deployed and monitored from the ship for up to 10 hours. After retrieval of the dredge basket, all samples will be cleaned, described, labeled and sorted for shore-based analyses.

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