High Resolution Dating of Louisville Guyots from IODP Sites U1372, U1375, U1376 and U1377: Implications for post-erosional hotspot ocean island processes and volcanism

Here we will present new ⁴⁰Ar/³⁹Ar Ages results from the International Ocean Drilling Project (IODP) Sites U1372 (n=18), U1375 (n=3), U1376 (n=15) and U1377 (n=7) during Expedition 330 that drilled the northern end of the Louisville Seamount trail. The Louisville Seamount trail displays age progressive volcanism thought to be formed as the Pacific plate moved over a hotspot. The older seamounts are located in the north (80 Ma, Osbourn Guyot) and younger seamounts to the south. Seamounts in this study are all guyots from the older section of the seamount trail (~74 Ma, Site U1372 at Canopus Guyot to ~51 Ma, Site U1377 at Hadar Guyot).

Sites U1372 and U1376 respectively recovered ~230 m and ~140 m of basaltic material beneath a thin sediment interface and contain many in-situ lava flows that are interlayed with volcaniclastics, breccias and intrusive sheets. ⁴⁰Ar/³⁹Ar measurements will be used to date these different lithologies and, along with paleomagnetic inclination data, determine whether there was post-erosional volcanism and postulate which processes are involved with either the construction or deconstruction of ocean islands. Koppers et al. (2012) noted that some holes had consistent paleomagnetic inclinations suggesting that at least the larger clasts in the volcaniclastic breccias were emplaced hot or otherwise had been reset post deposition. If this is the case and breccias were emplaced hot then this would explain the undetectable levels of CO₂ remaining in glasses after a complete degassing of the lithologies (Nichols et al., 2014). This would further support evidence for shallow eruption depths and post-erosional volcanism. In addition, the ⁴⁰Ar/³⁹Ar ages should be able to resolve whether or not the breccias were emplaced during the same time period as underlying and overlying intrusive sheets.

Samples were analyzed using a high-resolution incremental step-heating method at Oregon State University in the Geochronology Lab using a Thermo Scientific ARGUS-VI Noble Gas Multicollector Mass Spectrometer. All samples were treated with a rigorous acid leaching procedure to remove alteration products and carefully handpicked to avoid remaining visible alteration products.

Koppers, A. A. P. et al. (2012), Nature Geosci 5, 911–917. Nichols, A. R. L. et al. (2014), Geochem. Geophys. Geosyst. 15, 1718–1738.