Seismic evidence for a 1000 km mantle discontinuity under the Pacific

Abstract

Seismic discontinuities in the mantle are indicators of its thermo-chemical state and offer clues to its dynamics. Ray-based seismic methods, though limited by the approximations made, have mapped mantle transition zone discontinuities in detail, but have yet to offer definitive conclusions on the presence and nature of mid-mantle discontinuities. Here, we show how to use a wave-equation-based imaging method, reverse-time migration of precursors to surface-reflected seismic body waves, to uncover both mantle transition zone and mid-mantle discontinuities, and interpret their physical nature. We observe a thinned mantle transition zone southeast of Hawaii, and a reduction in impedance contrast around 410 km depth in the same area, suggesting a hotter-than-average mantle in the region. Here, we furthermore reveal a 4000–5000 km-wide reflector in new images of the mid mantle below the central Pacific, at 950–1050 km depth. This deep discontinuity exhibits strong topography and generates reflections with polarity opposite to those originating at the 660 km discontinuity, implying an impedance reversal near 1000 km. We link this mid-mantle discontinuity to the upper reaches of deflected mantle plumes upwelling in the region. Reverse-time migration full-waveform imaging is a powerful approach to imaging Earth’s interior, capable of broadening our understanding of its structure and dynamics and shrinking modeling uncertainties.

Deep‐Learning‐Based Prediction of the Tetragonal → Cubic Transition in Davemaoite

“…(2019). The mid‐mantle reflectors or scatters may be caused by other mechanisms, for example, the post‐stishovite phase transition in pure or aluminous‐hydrous silica (Umemoto et al., 2016; Wang et al., 2020) in stagnant subducted slabs (Zhang et al., 2023). Recently, Ko et al.…”

“…Therefore, the tetragonal to cubic transition in CaPv cannot explain the seismic wave speed anomalies in the lower mantle, contrary to the claim of Thomson et al (2019). The mid-mantle reflectors or scatters may be caused by other mechanisms, for example, the post-stishovite phase transition in pure or aluminous-hydrous silica (Umemoto et al, 2016;Wang et al, 2020) in stagnant subducted slabs (Zhang et al, 2023). Recently, Ko et al suggested that the dissolution behavior of CaPv in bridgmanite can lead to its disappearance as a separate phase at depths greater than 1,800 km, a new insight into the deep mantle mineralogy (Ko et al, 2022).…”

High‐Resolution Mantle Transition Zone Imaging Using Multi‐Dimensional Reconstruction of SS Precursors

“…More sophisticated solutions should properly consider the sensitivity kernel of SS precursors using migration or full waveform modeling (Koroni et al., 2017). The proposed method can offer a useful preconditioning tool to improve the quality of SS precursors for the pre‐stack migration imaging as has been investigated in a recent study (Z. Zhang et al., 2023).…”

“…The proposed method can offer a useful preconditioning tool to improve the quality of SS precursors for the prestack migration imaging as has been investigated in a recent study (Z. Zhang et al, 2023).…”

Data-space cross-validation of global tomographic models to assess mantle structure underneath the Pacific Ocean

“…Intricate plume structures comprising ponding zones (Nolet et al 2006;Wamba et al 2021Wamba et al , 2023 and branching networks have been imaged, e.g., in the Indian Ocean beneath La Réunion (Tsekhmistrenko et al 2021;Wamba et al 2023) and in the Antarctic Rift System beneath Marie Byrd Land (e.g., Hansen et al 2014). Beneath the Central Pacific around Hawaii, seismically slow material may have accumulated in the mid-mantle (Shen et al 2003;Yu et al 2018;Zhang et al 2023).…”