A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Emperor Seamounts at Jimmu Guyot. Issue 6 (2nd June 2022)

• Record Type: Journal Article
• Authors: Xu, C.; Dunn, R. A.; Watts, A. B.; Shillington, D. J.; Grevemeyer, I.; Gómez de la Peña, L.; Boston, B. B.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-02
• Subjects: Emperor Seamounts -- seismic tomography -- gravity modeling -- plate flexure -- oceanic crust -- seamount structure; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB023241
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: The intraplate Hawaiian‐Emperor Seamount Chain has long been considered a hotspot track generated by the motion of the Pacific plate over a deep mantle plume, and an ideal feature therefore for studies of volcanic structure, magma supply, plume‐crust interaction, flexural loading, and upper mantle rheology. Despite their importance as a major component of the chain, the Emperor Seamounts have been relatively little studied. In this paper, we present the results of an active‐source wide‐angle reflection and refraction experiment conducted along an ocean‐bottom‐seismograph (OBS) line oriented perpendicular to the seamount chain, crossing Jimmu guyot. The tomographic P wave velocity model, using ∼20, 000 travel times from 26 OBSs, suggests that there is a high‐velocity (>6.0 km/s) intrusive core within the edifice, and the extrusive‐to‐intrusive ratio is estimated to be ∼2.5, indicating that Jimmu was built mainly by extrusive processes. The total volume for magmatic material above the top of the oceanic crust is ∼5.3 × 10 4 km 3, and the related volume flux is ∼0.96 m 3 /s during the formation of Jimmu. Under volcanic loading, the ∼5.3‐km‐thick oceanic crust is depressed by ∼3.8 km over a broad region. Using the standard relationships between V p and density, the velocity model is verified by gravity modeling, and plate flexure modeling indicates an effective elastic thickness ( T e ) of ∼14 km. Finally, we find no evidence for large‐scale magmatic underplating beneath the pre‐existing crust. Plain Language Summary: As lithospheric plates move across mantle hotspots, melts will rise and pass through the plate to form a series of volcanos. The Hawaiian‐Emperor Seamount Chain is one of the Earth's most well‐known hotspot tracks and an ideal laboratory therefore for studying the nature and characteristics of volcano building and the extent to which oceanic plates bend under the weight of these volcanos, which is an indication of oceanic plate strength. As a major component of the chain, the Emperor Seamounts have been relatively little studied. To address these issues, we carried out an active‐source seismic imaging experiment across the Emperor Seamounts at Jimmu guyot. The seismic velocity image reveals that Jimmu has a core made from magmas that froze within its edifice but was built mainly by volcanic processes. Due to volcanic loading, the oceanic crust is depressed by ∼3.8 km. The density structure derived from the tomographic image well‐predicts observed gravity, while plate flexure modeling indicates an effective elastic thickness of ∼14 km, suggesting that the oceanic plate on which the Emperor chain was built was weaker at the time of volcano formation than the Hawaiian Ridge. Key Points: Seismic tomography experiment reveals crust and upper mantle structure along a 495‐km‐long east‐west line crossing the Emperor Seamounts Jimmu guyot was built mainly by extrusive processes, and the underlying ∼5.3‐km‐thick oceanic crust was depressed by ∼3.8 km There is no evidence for large‐scale magmatic underplating beneath the edifice