Deep plume origin of the Louisville hotspot: Noble gas evidence

Noble gas compositions have been reported for basaltic core samples from Louisville seamounts recovered during IODP Expedition 330. The in-vacuum crushing techniques were employed to extract noble gases from fresh olivine phenocrysts and submarine glasses with ages between 50 and 74 Ma. Stepwise crushing tests confirmed the extraction of magmatic noble gases from the olivine samples with minimal release of posteruption radiogenic nuclides; however, this was not always the case for the glass samples. The He-3/He-4 ratios of the studied samples range from a value similar to those of mid-ocean ridge basalts (MORB) to slightly elevated ratios up to 10.6 Ra. These ratios are not as high as those observed in other ocean island basalts, suggesting that the Louisville mantle plume was weak or the samples represent late-stage magmatic activity of the seamounts. However, two Louisville seamount basalts exhibit a primordial Ne isotopic signature that can be clearly discriminated from MORB Ne ratios. The He and Ne isotopic compositions of the Louisville seamount basalts can be explained by the mixing of less degassed mantle and depleted upper mantle with different He/Ne ratios. The presence of the less degassed mantle component in the source of the Louisville seamounts documents a deep origin of their mantle plume. Key Points Noble gases were measured for 50-74 Ma drilled samples from Louisville seamounts Louisville seamount basalts have primordial noble gas compositions Louisville seamount chains were formed by a deep-rooted mantle plume