GEOMORPHOLOGY AND GEOCHRONOLOGY OF TWO SEAMOUNTS IN THE WENTWORTH CHAIN, MID-PACIFIC

The mid to north Pacific basin is dotted with numerous seamounts, guyots, ridges and islands – most of which have not been explored or sampled. Unraveling the origin of these prominent seafloor features requires high-resolution multibeam mapping as well as analyses of recovered rock samples. The National Oceanic and Atmospheric Administration (NOAA) Ocean Explorer Program explored two seamounts in the southern extent of the Cretaceous-aged Wentworth Seamount Chain. Castellano Seamount (aka West Seamount; 26.43^oN, 177.8^oW) and an ‘Unnamed Seamount 3’ (25.36^oN, 178.43^oW) were explored with the ROV Deep Discoverer during expedition EX1603. These seamounts reside south of Midway Island, NW Hawaiian Ridge and likely represent the southern extent of the Wentworth Seamount Chain, which is an age-progressive seamount chain extending SE from Hess Rise (94-86 Ma; Pringle and Dalrymple, 1993). Alternatively, the seamounts may have formed contemporaneously with the NW Hawaiian Ridge during the Oligocene or formed ~120 Myrs ago on the ancient Pacific-Farallon spreading center. To test these different hypotheses, we present ⁴⁰Ar/³⁹Ar age determinations on two submarine basalt samples recovered from the seamounts. These age determinations are then combined with the new multibeam and ROV dive footage data from the seamounts to best interpret their geodynamic origin.