Browsing by Author "Yu, Chunquan"

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    A Displaced Lower Mantle Source of the Hainan Plume in South China Revealed by Receiver Function Imaging of the CEArray
    (Wiley, 2024) Zhang, Yan; Niu, Fenglin; Ning, Jieyuan; Yu, Chunquan
    We analyzed 49,592 teleseismic receiver functions (RFs) recorded by 278 CEArray stations to image the mantle transition zone (MTZ) beneath the South China Block to understand the origins of deep velocity anomalies and their potential links to subduction and intraplate volcanism. We employed a fast-marching method and a high-resolution 3-D velocity model (FWEA18) derived from full waveform inversion in computing P-to-S conversion times to better image the 410- and 660-km discontinuities. Our results indicate that the common-conversion-point stacking of RFs using 3-D conversion times yielded better migration images of the two discontinuities. The images revealed a slightly depressed 410-km with a few small uplifted patches, and showed that the 660-km beneath the western Yangtze Craton is depressed by 10–25 km, which is likely caused by the stagnant Paleo-Pacific slab. The 660-km beneath the southern Cathaysia Block has a 5–15 km high plateau with a topographic low at its central part. The lateral dimension of the topographic low is ∼150 km and is located beneath the central Pearl River Mount Basin near Hong Kong. We speculate that the topographic low occurs within the Hainan plume with a temperature excess of ∼300–400 K and is caused by the garnet phase transition. The displaced deep plume enters the MTZ and spreads nearly horizontally at the base. The plume evolves into two channels with a minor one toward the northeast and a major one toward the southwest, which keep moving upward to the 410-km. The southwest channel is likely the source that feeds the Hainan volcanoes.
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    Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii
    (Springer Nature, 2018) Yu, Chunquan; Day, Elizabeth A.; de Hoop, Maarten V.; Campillo, Michel; Goes, Saskia; Blythe, Rachel A.; van der Hilst, Robert D.
    Global seismic discontinuities near 410 and 660 km depth in Earth’s mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SSwaves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude–distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin. No such variations are found along the 410. The inferred 660 contrasts can be explained by mantle composition varying from average (pyrolitic) mantle beneath Hawaii to a mixture with more melt-depleted harzburgite southeast of the hotspot. Such compositional segregation was predicted, from petrological and numerical convection studies, to occur near hot deep mantle upwellings like the one often invoked to cause volcanic activity on Hawaii.
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    Mapping Mantle Transition Zone Discontinuities Beneath the Central Pacific With Array Processing ofﾠSSﾠPrecursors
    (Wiley, 2017) Yu, Chunquan; Day, Elizabeth A.; de Hoop, Maarten V.; Campillo, Michel; van der Hilst, Robert D.
    We image mantle transition zone (MTZ) discontinuities beneath the Central Pacific using ~120,000 broadband SS waveforms. With a wave packet‐based array processing technique (curvelet transform), we improve the signal‐to‐noise ratio of SS precursors and remove interfering phases, so that precursors can be identified and measured over a larger distance range. Removal of interfering phases reveals possible phase shifts in the underside reflection at the 660, that is, S660S, which if ignored could lead to biased discontinuity depth estimates. The combination of data quantity and improved quality allows improved imaging and uncertainty estimation. Time to depth conversions after corrections for bathymetry, crustal thickness, and tomographically inferred mantle heterogeneity show that the mean depths of 410 and 660 beneath the Central Pacific are 420 ± 3 km and 659 ± 4 km, respectively. The mean MTZ thickness (239 ± 2 km) is close to global estimates and suggests an adiabatic mantle temperature of ~1,400°C for the Central Pacific. Depth variations of the 410 and 660 appear to be relatively small, with peak‐to‐peak amplitudes of the order of 10–15 km. The 410 and 660 are weakly anticorrelated, and MTZ is thinner beneath Hawaii and to the north and east of the hotspot and thicker southwest of it. The relatively small discontinuity topography argues against the presence of large‐scale (more than 5° wide) thermal anomalies with excess temperatures over 200 K across the transition zone. The data used cannot exclude stronger thermal anomalies that are of more limited lateral extent or that are not continuous across the MTZ.