Is the Hawaiian Archipelago dominantly Loa-trend?

Abstract:

Hawaiian volcanoes are distributed en echelon on the islands along two chains, the Loa and Kea trends, that are geographically and geochemically distinct^1,2. These geochemical differences may be attributed to source zoning (concentric or bilateral) of the Hawaiian mantle plume (HMP) or to variations in pressure and temperature of melting. Most of these models assume a degree of independence of the two trends that is perhaps not realistic. To explore the isotopic characteristics of two “Kea”-trend volcanoes with transitional signatures, we analyzed 11 samples of Kohala shield-stage tholeiitic lavas and three from Haleakala for high-precision Pb-Nd-Sr-Hf isotopes. These samples are transitional in all isotopic systems between Loa and Kea compositions and cross-over the Pb-Pb boundary³. Minor cross-overs had been documented in Mauna Kea⁴, Kilauea⁵, and W Molokai⁶ basalts. A bilateral or concentric view of the HMP is thus too simplistic. Statistical analysis of the MC-ICP-MS or triple-spike shield tholeiite data (n>600) and the existence of three Pb-Pb trends originating from average Loa indicate that Loa is the dominant mantle source composition on the archipelago. Isotopically, four geochemical groups are identified: Kea (Mauna Kea, Kilauea), average Loa (Mauna Loa, Hualalai, Kauai, Waianae, W. Molokai, Loihi), enriched Loa (Koolau Makapuu, Lanai, Kahoolawe) and transitional Kea (E. Molokai, W. Maui, Haleakala, Kohala). The implications are: 1) HMP source components refresh and grade into and out of existence on a smaller timescale than previously thought; 2) the Kea trend is also heterogeneous; and 3) vertical heterogeneity of the plume is important on a regional scale as well as at the scale of individual volcanoes⁶.

¹Jackson et al., 1972, GSA Bull. 83, 1-17.

²Weis et al., 2011, Nat. Geosci., 4, 831-838.

³Abouchami et al., 2005, Nature, 434, 851-856.

⁴Eisele et al., 2003, G-cubed, 4, 5, 32 pages.

⁵Marske et al., 2007, EPSL, 259, 34-50.

⁶Xu et al., 2014, GCA, 132, 241-237.