Crustal structure along and surrounding the Hawaiian Islands: Volcanic island construction across scarred oceanic crust

Abstract

The Hawaiian Ridge is a classic example of an intraplate volcanic island chain emplaced on oceanic lithosphere. We seek to constrain both the deformation from island loading around the Hawaiian Ridge and the influence of the oceanic lithosphere, including the Molokaʻi fracture zone (MFZ), on off-axis volcanic emplacement. To examine these processes, we conducted a marine geophysical experiment in 2018 that included the acquisition of eight multichannel seismic reflection lines and used a 6,600 in 3 tuned air gun array and an ultra-long hydrophone streamer cable towed behind R/V Marcus G. Langseth across and around the southern Hawaiian Ridge. We image both the top of igneous oceanic crust and the Moho, and we observe significant variations in regional crustal structure and thickness variations, Moho characteristics, the locations of the buried MFZ, and the flexure of the Pacific oceanic lithosphere under the Hawaiian Ridge. We observe up to ∼4.5 km of deflection of the igneous oceanic crust in response to the volcanic load with sediment thickness increasing to ∼3–3.4 km near the ridge but not correlating with the deflection. A systematic difference in igneous oceanic crustal thickness is found north (average ∼5.2 km) and south (average ∼5.9 km), of the MFZ that also correspond to changes in Moho characteristics. The MFZ itself is associated with the largest crustal thickness variations (∼3.7–7.6 km). Magma ascent through these different crustal regions may account for some variations of magmatic flux to the surface along the Hawaiian Ridge.