Seismic structure along the Emperor Seamount Chain and flexural response of the lithosphere - preliminary results from RV Marcus G. Langseth cruise MGL1902

Despite the bathymetric prominence of seamount chains and their importance to a spectrum of geodynamic problems, we know little of their structure. The limited existing seismic data capable of imaging the velocity structure and crustal thickness of seamounts suggest that there is much diversity in their deep structure. Variability of seamount crustal structure can arise from differences in the composition or flux of magma from below or on controls by lithospheric flexure from above. Magma composition and flux vary on time scales of millions of years due to dynamical behavior of plumes, whereas deformation of the oceanic lithosphere is influenced by its thermal evolution through time, and is driven by loads imposed by volcanos as well as the swell-forming buoyant material. One of the best known seamount chains is the Hawaiian-Emperor chain in the NW Pacific. Seismic imagery of the deep crust of the Hawaiian Islands has been, and is being used to address the structure associated with recent (ages 0-5 Myr) volcano construction on old (~90 Myr) seafloor and correspondingly thick lithosphere. However, no crustal seismic imaging has ever been carried out along the northern domain of the chain—the Emperor seamounts—which are older (~65 Myr) volcanic products of the hotspot that formed on much younger seafloor (~20 Myr) and correspondingly thinner lithosphere. Here, we provide preliminary results from active source seismic refraction and wide-angle profiling along the chain, obtained May-June of 2019 during MGL1902 aboard the USA research vessel Marcus G. Langseth; data were acquired in a joint USA and German effort. Shots were fired using a tuned airgun array with a total volume of 6600 cubic-inches and were received on 21 ocean-bottom-seismographs (OBS) from GEOMAR, Kiel and 7 OBS from the American Ocean Bottom Seismic Instrument Center. Travel time data obtained from excellent-quality record sections show seismic energy on most OBS reaching >100 km. We use joint reflection and refraction tomographic inversion to yield the structure of the Emperor seamounts and the underlying oceanic plate upon which the seamounts where emplaced. Structural models from the crust and upper mantle will be produced with the aim of informing models that address the rheological properties of oceanic lithosphere and the mechanisms of swell formation.