Geochemistry and age data from the Manihiki Plateau (R/V SO193): Multiple volcanic events from EM1-FOZO-HIMU mantle sources within a single oceanic LIP

Widespread hardrock sampling of the Manihiki Plateau has been carried out in 2007 during the SO193 cruise with the German Research Vessel "Sonne" and thus far achieved the densest igneous sample coverage amongst insitu oceanic LIP's. Here we report new major- and trace element and Sr-Nd-Hf-Pb (Double Spike) isotopic data along with preliminary Ar/Ar ages. Volcanic rocks have been obtained from all structural and morphological units of the Manihiki area. These include the plateau basements of the Western, Northern and High Plateau exposed along their faulted margins and drilled at DSDP Site 317 on the Central High Plateau. Seamounts were sampled on the High Plateau (including Mt Eddie and Rakahanga sampled during SO67) and the Western Plateau. Additional seamounts were sampled within the Danger Islands Troughs (a series of NE-SW trending elongated basins that separate the Western from the High Plateau), the "High-North" Basin (between the Northern and High Plateau) and seamounts within the Samoan Basin immediately SW of the Manihiki Plateau. Available and our new Ar/Ar ages suggest that the plateau formed between c. 120 to 115 Ma followed by additional magmatic pulses between c. 100 to 80 Ma. While all seamounts have alkali-basaltic compositions with La/Yb > 3, the lavas of the plateau sampling sites divide into tholeiitic composition with La/Yb < 3 and alkali basalts similar to those of the seamount group. Therefore the faulted plateau edges comprise lava series reflecting temporal variations in the degree of melting and involvement of variably enriched and depleted mantle sources. Sr-Nd-Pb-Hf isotope variations further support contribution of distinct mantle sources over time. While the early tholeiitic plateau group (including DSDP site 317) lies on a mixing line of EM1 and FOZO; the late stage alkali basalts of the faulted plateau margins and seamounts form near identical mixing arrays between FOZO and HIMU. These observations in conjunction with our preliminary Ar/Ar age data suggest that at least three different mantle components contributed to the formation of the Manihiki Plateau over time. In particular EM1 and HIMU seem restricted to early and late stage magmatism respectively, whereas FOZO is present at all times. Since thermodynamic constraints exclude significant preservation of HIMU within the residual -LIP-forming- plume head, we suggest that a second large scale mantle melting event consisting of FOZO and HIMU mantle subsequently affected the SW Pacific region.