The Hawaiian Mantle Plume from Toe to Head along the Northwest Hawaiian Ridge

Abstract:

The Hawaiian-Emperor (HE) chain records ~82 Myr of volcanism¹ with two distinct geochemical and geographical trends, Kea and Loa, identified on the archipelago. The Northwest Hawaiian Ridge (NWHR) includes 51 volcanoes, spanning ~42 Myr between the bend in the HE chain and the Hawaiian Islands (47% of the HE chain²), that has no high-precision isotopic data aside from two volcanoes near the bend¹. Only Kea compositions have been observed on Emperor seamounts (>50 Ma)^1,3, whereas the Hawaiian Islands (<6.5 Ma) have both Kea and Loa lavas^3,4.

We have analyzed 23 samples of shield stage tholeiitic lavas from 13 NWHR volcanoes for Pb isotopes to test if the Loa trend exhibits a persistent presence along the ridge after Diakakuji seamount¹. Age corrected ²⁰⁶Pb/²⁰⁴Pb range from 17.870 at Diakakuji to 18.654 at Midway atoll. The most enriched Loa isotopic compositions are erupted at Diakakuji (comparable to Lanai), and Mokumanamana, West Nihoa, and Nihoa have isotopic compositions similar to Mauna Loa. These observations suggest an ephemeral presence of the Loa geochemical trend along the NWHR. When shield-stage lavas of each Hawaiian volcano is averaged, NWHR volcanoes shows the most and least radiogenic Pb of the entire HE dataset: Diakakuji (0.9703) and Midway (0.9247). The NWHR exhibits the most geochemically extreme lava compositions along a region where many geophysical parameters (volcanic propagation rate, magmatic flux, mantle potential temperature) were changing significantly^2,5. At a broader scale, correlation between radiogenic Pb and magmatic flux suggests source composition may control some of these changes, and help explain why the Hawaiian mantle plume seems to be strengthening⁵ rather than waning like classic plumes and LIPs.

¹Regelous et al., 2003, J. Pet., 44, 1, 113-140.

²Garcia et al., 2015, GSA Sp. Pap. 511.

³Tanaka et al., 2008, EPSL, 265, 450-465.

⁴Weis et al., 2011, Nat. Geosci., 4, 831-838.

⁵Vidal & Bonneville, 2004, J. Geophy. Res., 109.