The Rurutu Hotspot: Isotopic and Trace Element Evidence of HIMU Hotspot Volcanism in the Tuvalu Islands

Wednesday, 17 December 2014
Valerie Finlayson1, Jasper G Konter1, Kevin Konrad2, Anthony A P Koppers2 and Matthew G Jackson3, (1)University of Hawaii at Manoa, Department of Geology and Geophysics, Honolulu, HI, United States, (2)Oregon State University, College of Earth, Ocean, and Atmospheric Science, Corvallis, OR, United States, (3)University of California Santa Barbara, Department of Earth Sciences, Santa Barbara, CA, United States
Current Pacific absolute plate motion (APM) models include 2 major, long-lived hotspot tracks: the ~85 Ma Hawaiian-Emperor and the ~76 Ma Louisville tracks. Prior to ~50 Ma, these two hotspot tracks show significant inter-hotspot drift, mainly due to large southern motion of the Hawaiian hotspot [1,2]. A third track would allow for a more robust evaluation of the relationship between APM models and inter-hotspot drift.

We present trace element and Pb isotope evidence for a potential third long-lived Pacific hotspot trail—the Rurutu hotspot—anchored in the Cook-Austral Islands. Based on high 206Pb/204Pb ratios, 70-55 Ma volcanism in the Gilbert Ridge has been linked to the Rurutu hotspot [3]. The Gilbert Ridge may continue south into the Tuvalu Islands, where APM models predict that the Rurutu hotspot track captures the change in Pacific plate motion around 50 Ma at the intersection of Tuvalu and Samoa.

Sampling of the deep submarine flanks of atolls and seamounts in Tuvalu and westernmost Samoa took place during the 2013 RR1310 (R/V Roger Revelle) expedition. We present new Pb isotope and HFSE trace element data on 28 samples that support a Rurutu origin for Tuvalu volcanism and confirm HIMU signatures previously observed in 5 Tuvalu samples (206Pb/204Pb >20.1, several >21.0; 87Sr/86Sr < 0.705). Statistical tests indicate that Tuvalu HFSE element ratios show similarities with Cook-Austral HIMU and differences with Samoa EMII volcanism. Low Hf/Nb ratios are often a predictor of HIMU samples (206Pb/204Pb > 20.8). Moderately HIMU compositions (206Pb/204Pb = 20.0) correspond to slightly higher Hf/Nb. In an effort to test if compositional agreement with the Cook-Australs is reflected in an age progression, 40Ar/39Ar ages will be presented by Konrad et al. (this volume).

[1] Tarduno et al., (2003) DOI:10.1126/science.1086442

[2] Koppers et al., (2012) DOI: 10.1038/ngeo1638

[3] Konter et al., (2008) DOI: 10.1016/j.epsl.2008.08.023