A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Hawaiian Ridge: 1

• Published in: Journal of geophysical research. Solid earth 2023-12, Vol.128 (12), p.n/a
• Main Authors: MacGregor, B. G., Dunn, R. A., Watts, A. B., Xu, C., Shillington, D. J.
• Format: Article
• Language: English
• Subjects: Angle of reflection; Carbonates; Crustal thickness; Data acquisition; Deformation; Earth mantle; Elastic plates; Flexing; Gravity; Hawaiian ridge; Islands; Lithosphere; lithospheric flexure; marine gravity; Modelling; Oceanic crust; plate loading; Plate tectonics; Plates (tectonics); Platforms (geology); Reflectors; Sediments; Seismic activity; Seismic refraction; Seismic tomography; Seismic velocities; Thickness; Tomography; Travel time; Upper mantle; Velocity; Volcanic activity; Volcanism; volcano structure; Volcanoes; Wave velocity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2023JB027218

The Hawaiian Ridge has long been a focus site for studying lithospheric flexure due to intraplate volcano loading, but crucial load and flexure details remain unclear. We address this problem using wide‐angle seismic refraction and reflection data acquired along a ∼535‐km‐long profile that intersects the ridge between the islands of Maui and Hawai'i and crosses 80–95 Myr‐old lithosphere. A tomographic image constructed using travel time data of several seismic phases reveals broad flexure of Pacific oceanic crust extending up to ∼200–250 km either side of the Hawaiian Ridge, and vertically up to ∼6–7 km. The P‐wave velocity structure, verified by gravity modeling, reveals that the west flank of Hawaii is comprised of extrusive lavas overlain by volcanoclastic sediments and a carbonate platform. In contrast, the Hāna Ridge, southeast of Maui, contains a high‐velocity core consistent with mafic or ultramafic intrusive rocks. Magmatic underplating along the seismic line is not evident. Reflectors at the top and bottom of the pre‐existing oceanic crust suggest a ∼4.5–6 km crustal thickness. Simple three‐dimensional flexure modeling with an elastic plate thickness, Te, of 26.7 km shows that the depths to the reflectors beneath the western flank of Hawai'i can be explained by volcano loading in which Maui and the older islands in the ridge contribute ∼43% to the flexure and the island of Hawai'i ∼51%. Previous studies, however, revealed a higher Te beneath the eastern flank of Hawai'i suggesting that isostatic compensation may not yet be complete at the youngest end of the ridge. Plain Language Summary The Hawaiian Islands are one of Earth's best examples of a volcanic chain that formed on a tectonic plate that is moving over a fixed hotspot in the deep mantle. They are a “natural laboratory” for the study of intraplate volcanism and their impact on the large‐scale deformation of the plates. We carried out a seismic imaging experiment along a ∼535‐km‐long profile that intersected the chain between the islands of Maui and Hawai'i. The seismic velocity image reveals a high velocity, high density, “core” within part of the chain and that the combined weight of the edifices that make up each island has flexed the Pacific oceanic plate down by up to ∼6–7 km over distances of up to 400–500 km. There is evidence that the elastic thickness of the Pacific lithosphere may be higher for Hawai'i than for the older islands in the Hawaiian ridge, suggesting that the adjustmen