Segregated oceanic crust trapped at the bottom mantle transition zone revealed from ambient noise interferometry

Abstract

The recycling of oceanic crust, with distinct isotopic and chemical signature from the pyrolite mantle, plays a critical role in the chemical evolution of the Earth with insights into mantle circulation. However, the role of the mantle transition zone during this recycling remains ambiguous. We here combine the unique resolution reflected body waves (P410P and P660P) retrieved from ambient noise interferometry with mineral physics modeling, to shed new light on transition zone physics. Our joint analysis reveals a generally sharp 660-km discontinuity and the existence of a localized accumulation of oceanic crust at the bottom mantle transition zone just ahead of the stagnant Pacific slab. The basalt accumulation is plausibly derived from the segregation of oceanic crust and depleted mantle of the adjacent stagnant slab. Our findings provide direct evidence of segregated oceanic crust trapped within the mantle transition zone and new insights into imperfect whole mantle circulation.

Autocorrelation R2 on Mars

“…Seismic interferometry has been widely applied to retrieve the empirical Green's functions of surface waves (Berg et al., 2018; Miao et al., 2022; Qiu et al., 2020, 2021; Schimmel et al., 2018; Shen et al., 2013; Yao et al., 2006) and body waves (Clayton, 2020; Feng et al., 2017, 2021; Gorbatov et al., 2013; Kennett, 2015; Oren & Nowack, 2017; She et al., 2022) from ambient noise auto‐ and cross‐correlations. Many ambient noise surface wave tomography studies on Earth have focused on the calculations of the Rayleigh wave phase velocity to invert for the S‐wave velocity of sedimentary basins (Cai et al., 2022; Hannemann et al., 2014; Pan et al., 2016; Qiu et al., 2019; Shirzad & Shomali, 2014), the crust and upper mantle (Li et al., 2012; Lin et al., 2014; Nguyen et al., 2022; Yao et al., 2008; Zhang et al., 2018).…”

Basaltic reservoirs in the Earth’s mantle transition zone

“…This density crossover at 660 km depth is thought to promote basalt accumulation near the base of the mantle transition zone (MTZ), but the high viscosity of cold and stiff subducted slabs may prevent efficient separation (segregation) of the basaltic crust from the subducting slab ( 5 , 6 ). Indeed, there are few indications of anomalous basalt enrichment at MTZ depth near downwellings ( 7 – 11 ), and geodynamic models generally favor segregation near the hot core–mantle boundary ( 6 , 12 ).…”

Likely P‐to‐S Conversion at the Core‐Mantle Boundary Extracted From Array Processing of Noise Records

“…Array stacking requires array data, which limits its application, although the required array density likely depends on the targeted seismic phase. So far, most of the seismic imaging studies using body‐wave noise have not accounted for its spatiatemporal variation and have relied simply on stacking large number of cross‐correlation functions (e.g., Feng et al., 2021; Poli et al., 2012). Our results suggest that the primary contribution to their signals may have only come from a fraction of all the time windows, and that simply selecting those time windows might significantly improve the signal quality (Figure 3).…”

“…This observation is commonly attributed to the prominence of surface waves in Earth's noise field as a result of noise sources, such as wind and ocean waves, occurring mostly at the surface. Despite their lower amplitudes, body‐wave signals have occasionally been retrieved from noise cross‐correlations and used to image Earth structure (e.g., Feng et al., 2021; Nakata et al., 2015; Pedersen and Colombi, 2018; Poli et al., 2012). A major advantage of body waves over surface waves in studying Earth structure is that body‐wave reflected and converted phases are sensitive to material discontinuities in Earth's interior (e.g., the Moho and the core‐mantle boundary [CMB]), which cannot be resolved with surface‐wave data alone.…”