Abstract
Seismic anisotropy could provide vital information about the evolution and internal convection of the deep Earth interior. Although previous seismological studies have revealed a wide distribution of seismic anisotropy in the upper portion of the lower mantle beneath many subduction zones, the existence of anisotropy at these depths away from subducted slabs remains debated. Here we use P-wave azimuthal anisotropy tomography to image the crust and mantle down to 1,600-km depth. We find prominent anisotropic patterns in the upper portion of the lower mantle beneath the Philippine Sea Plate. Substantial azimuthal anisotropy with NāS fast-velocity directions occurs at 700ā900-km depths. We interpret this azimuthal anisotropy as a remnant of the Pacific lower mantle flow field about 50 million years ago. Two isolated high-velocity anomalies at 700ā1,600-km depths may be vestigial pieces of the subducted Izanagi slab with seismic velocity features suggesting a shift in the Pacific lower mantle flow field by about 40 million years ago. Our findings provide seismic evidence for the existence of complex lower mantle flows and deformation mechanisms away from subduction zones.
Similar content being viewed by others
Main
As an important layer, the lower mantle may play a critical role in the evolution and material cycle of the Earth interior. Therefore, it is important to better understand geodynamics of the lower mantle. It has been widely accepted that plate subduction and mantle plumes are two main styles in the evolution and material cycle of the Earthās surface and interior, which have been proven by global seismic tomography1,2. In these processes, the lower mantle is of great importance, which is not only the eventual destination of subducted slabs but also the birthplace of mantle plumes3. However, our knowledge on the geodynamical property of the lower mantle is still deficient.
As a valuable and useful tool in understanding geodynamics of the deep Earth processes, seismic anisotropy has been widely used to characterize deformations of the crust and lithosphere and flows in the mantle, providing vital information on the evolution and internal convection of the deep Earth interior, particularly in subduction zones4,5. Compared with the crust and upper mantle that are generally considered to be seismically anisotropic, most parts of the lower mantle are regarded to be seismically isotropic, although highly anisotropic minerals, such as bridgmanite and ferropericlase, are generally considered to be the major ingredients in the lower mantle6,7. This may depend on the predominant deformation mechanisms, such as diffusion or superplastic creep8,9 and/or pure climb creep10 in the bulk of the lower mantle.
To date, some shear-wave splitting measurements have suggested the presence of prominent seismic anisotropy in the upper portion of the lower mantle (UPLM) beneath several subduction zones11,12,13,14,15. In addition, a whole-mantle shear-wave anisotropic model suggests a wide distribution of seismic anisotropy in the UPLM beneath major subduction zones16. A mechanism of dislocation creep deformation caused by slab subduction is proposed to largely account for the UPLM seismic anisotropy17,18. However, these observations mainly focused on the vicinity of subducted slabs; the existence of seismic anisotropy away from the subducted slabs in the UPLM is still highly debated.
The Philippine Sea Plate (PSP) surrounded by subduction zones (Fig. 1) provides a valuable area to study the seismic structure and geodynamics away from the subducted slabs in the UPLM because of the extremely high seismicity. Many studies of seismic anisotropy in and around the PSP have been made19,20,21,22,23,24,25, which have provided important information on the structure, dynamics and evolution of the PSP. However, up to now, seismic anisotropy in the UPLM beneath the PSP has not been revealed.
Azimuthal anisotropy in the UPLM beneath the PSP
In this work, we conducted P-wave azimuthal anisotropy tomography to image the detailed three-dimensional (3-D) anisotropic structure of the crust and mantle down to 1,600-km depth beneath the PSP. Our tomographic images at different depths exhibit complex azimuthal anisotropy patterns (Fig. 2aāf and Supplementary Fig. 1), which are generally consistent with the previous results19,20,21,22,23,24,25. The most prominent feature of our azimuthal anisotropy tomography is NāS fast-velocity directions (FVDs) at depths of 700ā900ākm beneath the middle PSP, which are bounded by NWāSE FVDs to the northeast beneath the northern PSP (Fig. 2aāc). The NWāSE FVDs beneath the northern PSP extend from 300- to 1,600-km depths (Fig. 2aāf and Supplementary Fig. 1eāh), suggesting that the upper and lower mantle flow fields beneath the Pacific Plate are moving northwestward simultaneously. The different FVD features in the UPLM beneath the middle PSP and the Pacific Plate indicate that the present mantle flow patterns beneath the two plates are distinct.
Remnant of the Pacific lower mantle flow field 50 million years ago
The prominent NāS FVDs at 700ā900-km depths beneath the middle PSP (Fig. 2aāc) seem to be less affected by the slab subduction because they occur generally away from the present subduction zones. In addition, previous seismic anisotropy studies revealed that the UPLM is generally characterized by trench-parallel FVDs11,12,13,14,15,16, which are possibly caused by interactions between the subducted slab and the lower mantle inducing high differential stresses and dislocation creep16. Similarly, surface-wave anisotropic tomography revealed prominent anisotropies in the UPLM away from subduction zones beneath central Asia26. But they were still suggested to be connected with subducted slabs, because they are located in a large high-velocity (high-V) anomaly and may reflect strong interactions between the subducted Tethys, Izanagi and Pacific plates26. Different from central Asia, no high-V anomaly appears in the area where the prominent NāS FVDs are revealed by our azimuthal anisotropy tomography (Fig. 2aāc). Hence, we infer that these NāS FVDs are independent of the slab subduction.
Another proposed cause of the UPLM anisotropy is lateral lower mantle flow associated with a mantle plume14. A recent study of P-wave azimuthal anisotropy tomography has revealed similar NāS FVDs in a large-scale low-velocity (low-V) anomaly at depths of 1,300ā1,600ākm beneath Borneo, Southeast Asia27, which are approximately parallel to the subduction direction and possibly reflect lateral movement of a mantle plume beneath the Java subduction zone28. This tomography also shows large high-V anomalies above the NāS FVDs, which reflect subducted slabs. This result may further indicate that the rising of the mantle plume beneath the Java subduction zone is impeded by the subducted slabs and results in the lateral mantle flow and the NāS FVDs. However, our tomography does not disclose a prominent low-V anomaly at 700ā1,600-km depths beneath the PSP (Fig. 2aāf and Supplementary Fig. 3). If the NāS FVDs in our tomography were generated by lateral movement of a low-V anomaly, the lower mantle material would rise through the mantle transition zone and arrive at the PSP seafloor, simply because there is no subducted slab indicated by a high-V anomaly in the mantle transition zone beneath the southern PSP (Supplementary Figs. 1g,h and 2g,h). Thus, if a low-V mantle plume exists in the UPLM there, its rising would not be blocked. Nevertheless, geochemical studies have shown that basalts related to a mantle plume exist only in the Benham and Urdaneta plateaus29,30 between 35 and 40 million years ago (Ma), suggesting that the mantle plume may have been inactive since then. Therefore, we deem that possible lateral flow of the lower mantle material may have contributed little to our observed NāS FVDs.
Some geodynamic simulations suggested that complete subduction and detachment of the Izanagi Plate induced an important transformation of the lower mantle flow beneath the Pacific Plate, from slow southward motion at 60āMa to fast northward motion at 50āMa, and further to be northwestward at 40āMa31. The NWāSE FVDs at 300ā1,600-km depths beneath the northern PSP (Fig. 2 and Supplementary Fig. 1eāh) and the NāS FVDs at 700ā900-km depths beneath the middle PSP revealed by our anisotropy tomography are highly consistent with the northwestward and northward movements of the lower mantle flow beneath the Pacific Plate at 40 and 50āMa, respectively, as suggested by those geodynamic simulations. Therefore, we infer that the NWāSE FVDs at 300ā1,600-km depths may further reflect the stable northwestward movement of the upper and lower mantle flow fields beneath the Pacific Plate since about 40āMa, and the NāS FVD at 700ā900-km depths beneath the middle PSP is an indicator of the remnant Pacific lower mantle flow field at about 50āMa (Fig. 3).
Seismological studies detected seismic scatterers at 1,000ā1,800-km depths under east of the IzuāBonināMariana Trench (Supplementary Fig. 3dāf), which are suggested to be an ancient subducted oceanic slab and not related with the contemporary subducting Pacific slab along the IzuāBonināMariana Trench32,33. They may be carried northward 500ā1,000ākm from the present Mariana Trench due to oblique subduction34. These seismic scatterers are in good accordance with one high-V anomaly at 1,100ā1,600-km depths beneath the southern IzuāBonin Trench revealed by our isotropic tomography (H1 in Supplementary Fig. 3dāf), which also shows that H1 is disconnected with the subducting Pacific slab along the IzuāBonināMariana Trench (Supplementary Fig. 4). Hence, H1 probably reflects the ancient subducted oceanic slab. Similar features were also observed at 930ā1,120ākm depths beneath Northeast China and the adjacent Japan Sea, which are suggested to be a piece of remnant of the subducted Izanagi slab before the present subducting Pacific slab along the IzuāBonināMariana Trench35. Consequently, we suggest that H1 is another piece of remnant of the subducted Izanagi slab, whose time to sink down to ~1,000-km depth was estimated to be 45ā60 million years35. This timescale coincides well with some plate reconstruction results based on tomographic results along the Mariana Trench36. They suggest that the Mariana Trench has been at its present location (with Ā±200-km uncertainties) since the subduction initiation of the Pacific Plate beneath the PSP in the early Cenozoic, because tomographic results show that the subducted Pacific slab along the Mariana Trench has a length of over 1,000ākm36. This argument is supported by the location of H1 and its separation from the subducting Pacific slab along the IzuāBonināMariana Trench, considering that H1 may have moved northwards for a distance of 500ā1,000ākm34. Hence, we infer that the Pacific Plate has been continuously subducting along the Mariana Trench since the early Cenozoic. When the subducted Pacific slab from the Mariana Trench reached the UPLM, the lower mantle flow field at 700ā900-km depths beneath the PSP would be separated from and not influenced by that beneath the Pacific Plate, leading to the maintenance of the remnant of the Pacific lower mantle flow from about 50āMa to the present.
Remnant of the Pacific lower mantle flow field at about 40āMa
Besides H1 (Fig. 2aāg), another isolated high-V anomaly (H2 in Fig. 2cāf,h) is also characterized by similar NWāSE FVDs. The locations of H1 and H2 are generally consistent with that of the spreading centre between the Izanagi and Pacific plates when this spreading centre was about to subduct beneath the Eurasian Plate37. Thus, we infer that H2 is another remnant of the subducted Izanagi slab.
The NWāSE FVDs in H1 (Fig. 2) may reflect the stable northwestward movement of the lower mantle flow field beneath the Pacific Plate since ~40āMa because the NWāSE FVDs in H1 are consistent with those in the upper mantle and the mantle transition zone (Supplementary Fig. 1eāh). However, the NWāSE FVDs in H2 are greatly different from those in the surrounding lower mantle at the same depths and those at the same location in the upper mantle and the mantle transition zone (Fig. 2cāf and Supplementary Fig. 1), which may indicate that the anisotropy in H2 is not influenced by the present lower mantle flow. Considering that H1 and H2 are not connected, and both of them are remnants of the subducted Izanagi slab with similar anisotropic features, we infer that H2 possibly preserves the remnant of the Pacific lower mantle flow field at about 40āMa (Fig. 3). This may be ascribed to the amorphous mantle flow field around H2 as shown by the slightly disordered FVDs around H2 at 900ā1,600-km depths (Fig. 2cāf). Hence, H2 may not have experienced phase transition associated with mantle convection but preserve its fossil frozen-in anisotropy.
The above process is analogous to the preservation of primitive mantle materials in the lower mantle. Recent geodynamic models suggest that intrinsically stable and strong bridgmanite-enriched ancient mantle structures (BEAMSs) exist in the lower mantle, which could sustain the lateral heterogeneity of the lower mantle for billions of years and are less affected by subducting slabs and mantle plumes38. The existence of the primitive mantle materials is also suggested by mineral physics and geochemical studies39,40,41. Recent studies have suggested that these BEAMSs may have a high viscosity contrast of ā¼10ā50 times in the deep mantle reservoir with a small scale42 and a grain size less than several hundred micrometres43 to retain their primordial signature. The small-scale trait of these BEAMSs may allow them to be carried by mantle flow and move to the surface or other places in the Earth40. Although the primitive mantle materials in the lower mantle are not revealed by this study, our anisotropic tomography shows that the former lower mantle flow field can be maintained for dozens of millions years, suggesting that the preservation of primitive mantle materials in the lower mantle for several billion years is quite possible.
Our anisotropic tomography suggests that seismic anisotropy in the lower mantle may be much more prevalent than previously thought, not only in the vicinity of the subducting slabs but also away from the slabs. The clear UPLM anisotropy we observed further suggests that dislocation creep may play a more important role in the deep Earth interior than commonly believed. These observations also provide important and independent seismic evidence for the existence of past deformations within the lower mantle, which may stimulate future geodynamical modelling to better understand the deformation mechanisms, rheology and thermodynamic and thermoelastic properties of minerals in the deep mantle.
Methods
Data
The P-wave arrival-time data utilized in this study are comprised of three parts. The first part includes P-wave arrival-time data of local, regional and teleseismic events recorded at land-based stations (green triangles in Fig. 1) collected from the International Seismological Centre (ISC)-EHB database (http://www.isc.ac.uk/isc-ehb/search/arrivals/) from 1964 to 2019, in which all the events are well relocated using the EHB algorithm45. The second part consists of P-wave arrival-time data of local and regional earthquakes recorded at ocean bottom seismometers deployed by the Ocean Hemisphere Project46 (red triangles in Fig. 1; http://ohpdmc.eri.u-tokyo.ac.jp/). The third part includes P-wave arrival-time data of local and regional earthquakes recorded at ocean bottom seismometers in the Yap subduction zone47 (purple triangles in Fig. 1), which were deployed and retrieved by the Institute of Oceanology, Chinese Academy of Sciences, using the research Vessel KEXUE. The P-wave arrival times of local and regional events recorded at the ocean bottom seismometers are manually picked based on theoretical arrival times computed for the IASP91 Earth model48 and merged with the ISC-EHB data.
Then we carefully sifted the data of local and regional events according to the following criteria: (1) each earthquake was recorded at more than four stations in the study region; (2) the arrivals with epicentral distance >200ākm are used in the inversion, because we mainly focus on large-scale velocity structures of the mantle and (3) the absolute value of raw travel-time residuals is smaller than 2.5ās. Finally, our dataset contains 1,005,690 P-wave arrival times of 50,345 local and regional events recorded at 1,235 stations, including 1,635 arrivals at 56 ocean bottom seismometers (Supplementary Fig. 7a).
For the teleseismic events, the selection criteria are as follows: (1) each event was recorded at more than five seismic stations in the study region; (2) the absolute value of each travel-time residual is smaller than 3.0ās; (3) the epicentral distance between a teleseismic event and a station is in a range of 30ā100Ā°. As a result, 294,213 P-wave arrivals of 20,607 teleseismic events are selected to use in this study (Supplementary Fig. 7b).
Azimuthal anisotropic and isotropic tomographic inversions
To determine the 3-D azimuthal anisotropy and isotropic P-wave velocity (Vp) models beneath the PSP, we use the azimuthal anisotropic and isotropic tomographic methods49,50. In the anisotropic tomographic method, weak azimuthal anisotropy with a horizontal axis of hexagonal symmetry is assumed. Thus, P-wave slowness (that is, 1āVpā1) in an arbitrary propagation direction can be approximately expressed as:
where S is the total slowness, S0 is isotropic slowness, A and B are two azimuthal anisotropy parameters, and \({{\varnothing }}\) is ray path azimuth. The fast-velocity direction (FVD) \({\rm{\psi }}\) and the azimuthal anisotropy amplitude Ī± can be expressed as follows:
For the isotropic tomography, 3-D grid nodes are arranged in the study volume with a lateral grid interval of 1.0Ā°, whereas for the anisotropic tomography, 3-D grid nodes are set with a lateral grid interval of 2.0Ā°, because compared to isotropic Vp tomography, a better coverage of rays in azimuth and incident angle is required to obtain robust Vp anisotropic tomography. In the vertical direction, the grid nodes are set at depths of 20; 50; 100; 200; 300; 400; 500; 600; 700; 800; 900; 1,100; 1,300 and 1,600ākm. We adopt an updated Vp model as the one-dimensional (1-D) initial model, which is integrated from the CRUST1.0 model51, the WPSP01P model52 and the IASP91 Earth model48, similar to our previous studies19,20. The 1-D initial Vp model includes four velocity discontinuities, that is, the Conrad, Moho, 410 and 660ākm discontinuities. Using this initial 1-D Vp model, we relocate all the local and regional earthquakes. Then we conduct the azimuthal anisotropy and isotropic tomographic inversions using the Least Squares with QR factorization (LSQR) algorithm53 with damping and smoothing regularizations. Considering the trade-off between the root mean square (RMS) travel-time residual and the norm of a 3-D Vp model, the optimal damping and smoothing parameters are found to be 500.0 and 20,000.0, respectively (Supplementary Fig. 8), after conducting many tomographic inversions with different values of the damping and smoothing parameters. After the isotropic and anisotropic inversions (Supplementary Fig. 9), the RMS travel-time residual is reduced from 1.305ās for the initial 1-D Vp model to 1.075ās for the 3-D isotropic Vp model and further reduced to 1.034ās for the 3-D Vp azimuthal anisotropic model. The RMS residual reductions are found to be statistically significant after performing the F-test19,54.
Resolution analysis
To evaluate the resolution and robustness of the main features of our azimuthal anisotropy tomographic model and the trade-off between the isotropic Vp and azimuthal anisotropy, we performed a number of chequerboard resolution tests (CRTs) and restoring resolution tests (RRTs). In the CRTs, three kinds of input models with different values of the isotropic Vp and azimuthal anisotropy parameters are constructed. In the first to third input models, the isotropic Vp perturbations are assigned to be Ā±2%, 0% and Ā±2%, whereas perturbations of the anisotropic parameters (A and B) are Ā±2%, Ā±2% and 0%, respectively. According to equation (2), the input FVDs at two neighbouring grid nodes are normal to each other with an amplitude of 2%. In the RRTs, four input models with different azimuthal anisotropy parameters are constructed: (1) NāS FVDs with an amplitude of 2% beneath the middle PSP at depths of 700ā900ākm; (2) EāW FVDs with an amplitude of 2% beneath the middle PSP at depths of 700ā900ākm; (3) NWāSE FVDs with an amplitude of 2% beneath the northeastern PSP at depths of 300ā1,600ākm and (4) NWāSE FVDs with an amplitude of 2% in the anomaly H2 at depths of 900ā1,600ākm. Then theoretical travel times are calculated for each input model, and the same ray paths as in the observed dataset are used. To simulate picking errors of the arrival-time data, we add Gaussian noise (ā0.25 to +0.25ās) with a standard deviation of 0.1ās to the synthetic travel times, which are then inverted to obtain an output model. Comparing the input and output models, we can judge whether the input model can be well recovered or not.
Supplementary Figs. 10ā25 show the obtained CRT and RRT results. The CRT results (Supplementary Figs. 10ā13) indicate that the resolution is generally good beneath most of the study region, except for the central and marginal areas at depths of 20-300ākm, where the seismic rays do not crisscross very well (Supplementary Fig. 26). The tomographic results, especially the azimuthal anisotropic images, have a spatial resolution of 2.0Ā° at depths of 20ā800ākm and 4.0Ā° at depths of 900ā1,600ākm (Supplementary Figs. 10ā13). Supplementary Figs. 14ā21 show the CRT results for assessing the trade-off between the isotropic Vp and azimuthal anisotropy, which indicate that the trade-off does exist but it mainly occurs in the marginal areas where the resolution is low due to the imperfect ray coverage. As a whole, the trade-off between the isotropic Vp and azimuthal anisotropy is insignificant, and our azimuthal anisotropy tomography is reliable. Four RRTs are performed to further evaluate the robustness of the main features of our isotropic Vp and azimuthal anisotropy tomographic results, such as the NāS FVDs at depths of 700ā900ākm beneath the middle PSP (Supplementary Figs. 22ā23), the NWāSE FVDs beneath the northeastern PSP at depths of 300ā1,600ākm (Supplementary Fig. 24) and the NWāSE FVDs in H2 beneath the middle PSP at depths of 900ā1,600ākm (Supplementary Fig. 25). These RRT results indicate that all the input isotropic Vp and azimuthal anisotropy patterns, including the amplitude and FVDs, can be generally well recovered. Although slight smearing occurs in some areas, it does not affect the main features of our tomography.
We further performed three more RRTs to investigate the effect of Vp radial anisotropy on the NāS FVDs at 700ā900-km depths beneath the middle PSP. In these tests, the input models contain negative radial anisotropy (that is, vertical Vpā>āhorizontal Vp) with an amplitude of 1% at 700ā900-km and 20ā600-km depths at 9ā25Ā°āN latitudes and 20ā1,100-km depths at 9ā35Ā°āN, respectively. Then we conducted azimuthal anisotropic inversions. The test results (Supplementary Figs. 27ā29) show that although some artifacts of isotropic Vp and azimuthal anisotropy show up at some depths, they are quite different from our results of isotropic Vp and azimuthal anisotropy. Hence, the NāS FVDs at 700ā900-km depths beneath the middle PSP are not caused by radial anisotropy.
Data availability
The P-wave arrival-time data used in this study are available at http://www.isc.ac.uk/isc-ehb/search/arrivals/, https://doi.org/10.12157/IOCAS.20211110.002, http://ohpdmc.eri.u-tokyo.ac.jp and https://doi.org/10.12157/IOCAS.20230828.001. The 3-D velocity model can be requested from the corresponding authors.
Code availability
The free software GMT (https://www.generic-mapping-tools.org/) was used in this study. The analysis codes and related scripts for generating figures used in the main text and Supplementary Information are available from the corresponding authors upon reasonable request.
References
van der Hilst, R., Widiyantoro, S. & Engdahl, E. Evidence for deep mantle circulation from global tomography. Nature 386, 578ā584 (1997).
Zhao, D. Seismic structure and origin of hotspots and mantle plumes. Earth Planet. Sci. Lett. 192, 251ā265 (2001).
Garnero, E. J. & McNamara, A. K. Structure and dynamics of Earthās lower mantle. Science 320, 626ā628 (2008).
Long, M. D. Constraints on subduction geodynamics from seismic anisotropy. Rev. Geophys. 51, 76ā112 (2013).
Zhao, D., Liu, X., Wang, Z. & Gou, T. Seismic anisotropy tomography and mantle dynamics. Surv. Geophys. 44, 947ā982 (2023).
Wang, X., Tsuchiya, T. & Hase, A. Computational support for a pyrolitic lower mantle containing ferric iron. Nat. Geosci. 8, 556ā559 (2015).
Kurnosov, A., Marquardt, H., Frost, D. J., Ballaran, T. B. & Ziberna, L. Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data. Nature 543, 543ā546 (2017).
Karato, S. I. & Li, P. Diffusion creep in perovskite: implications for the rheology of the lower mantle. Science 255, 1238ā1240 (1992).
Karato, S. I., Zhang, S. & Wenk, H. R. Superplasticity in Earthās lower mantle: evidence from seismic anisotropy and rock physics. Science 270, 458ā461 (1995).
Boioli, F. et al. Pure climb creep mechanism drives flow in Earthās lower mantle. Sci. Adv. 3, e1601958 (2017).
Foley, B. J. & Long, M. D. Upper and mid-mantle anisotropy beneath the Tonga slab. Geophys. Res. Lett. 38, L02303 (2011).
Lynner, C. & Long, M. D. Sub-slab anisotropy beneath the Sumatra and circum-Pacific subduction zones from source-side shear wave splitting observations. Geochem. Geophys. Geosyst. 15, 2262ā2281 (2014).
Wookey, J., Kendall, J. M. & Barruol, G. Mid-mantle deformation inferred from seismic anisotropy. Nature 415, 777ā780 (2002).
Wookey, J. & Kendall, J. M. Evidence of midmantle anisotropy from shear wave splitting and the influence of shear-coupled P wave. J. Geophys. Res. 109, B07309 (2004).
Zhu, H., Stern, R. J. & Yang, J. Seismic evidence for subduction-induced mantle flows underneath Middle America. Nat. Commun. 11, 2075 (2020).
Ferreira, A. M. G., Faccenda, M., Sturgeon, W., Chang, S. J. & Schardong, L. Ubiquitous lower-mantle anisotropy beneath subduction zones. Nat. Geosci. 12, 301ā306 (2019).
Cordier, P., UngĆ”r, T., Zsoldos, L. & Tichy, G. Dislocation creep in MgSiO3 perovskite at conditions of the Earthās uppermost lower mantle. Nature 428, 837ā840 (2004).
Tsujino, N. et al. Mantle dynamics inferred from the crystallographic preferred orientation of bridgmanite. Nature 539, 81ā84 (2016).
Fan, J. & Zhao, D. P-wave anisotropic tomography of the central and southern Philippines. Phys. Earth Planet. Inter. 286, 154ā164 (2019).
Fan, J. & Zhao, D. P-wave tomography and azimuthal anisotropy of the ManilaāTaiwanāSouthern Ryukyu region. Tectonics 40, e2020TC006262 (2021).
Isse, T. et al. Anisotropic structures of the upper mantle beneath the northern Philippine Sea region from Rayleigh and Love wave tomography. Phys. Earth Planet. Inter. 183, 33ā43 (2010).
Ma, J., Tian, Y., Zhao, D., Liu, C. & Liu, T. Mantle dynamics of Western Pacific and East Asia: new insights from P-wave anisotropic tomography. Geochem. Geophys. Geosyst. 20, 3628ā3658 (2019).
Qiao, Q. et al. Upper mantle structure beneath Mariana: insights from Rayleigh-wave anisotropic tomography. Geochem. Geophys. Geosyst. 22, e2021GC009902 (2021).
Wei, W., Zhao, D., Xu, J., Wei, F. & Liu, G. P and S wave tomography and anisotropy in Northwest Pacific and East Asia: constraints on stagnant slab and intraplate volcanism. J. Geophys. Res. 120, 1642ā1666 (2015).
Wei, W., Zhao, D., Yu, W. & Shi, Y. Complex patterns of mantle flow in eastern SE Asian subduction zones inferred from P-wave anisotropic tomography. J. Geophys. Res. 127, e2021JB023366 (2022).
Montagner, J. P., Burgos, G., Capdeville, Y., Beucler, E. & Mocquet, A. The mantle transition zone dynamics as revealed through seismic anisotropy. Tectonophysics 821, 229133 (2021).
Hua, Y., Zhao, D. & Xu, Y. G. Azimuthal anisotropy tomography of the Southeast Asia subduction system. J. Geophys. Res. 127, e2021JB022854 (2022).
MĆ©riaux, C. A. et al. Mantle plumes in the vicinity of subduction zones. Earth Planet. Sci. Lett. 454, 166ā177 (2016).
Ishizuka, O., Taylor, R. N., Ohara, Y. & Yuasa, M. Upwelling, rifting, and age-progressive magmatism from the Oki-Daito mantle plume. Geology 41, 1011ā1014 (2013).
Yan, Q., Shi, X., Yuan, L., Yan, S. & Liu, Z. Tectono-magmatic evolution of the Philippine Sea Plate: a review. Geosyst. Geoenviron. 1, 100018 (2022).
Seton, M. et al. Ridge subduction sparked reorganization of the Pacific plate-mantle system 60-50 million years ago. Geophys. Res. Lett. 42, 1732ā1740 (2015).
Kaneshima, S. Seismic scatterers in the lower mantle near subduction zones. Geophys. J. Int. 219, S2āS20 (2019).
Rost, S., Garnero, E. J. & Williams, Q. Seismic array detection of subducted oceanic crust in the lower mantle. J. Geophys. Res. 113, B06303 (2008).
Castle, J. C. & Creager, K. C. A steeply dipping discontinuity in the lower mantle beneath Izu-Bonin. J. Geophys. Res. 104, 7279ā7292 (1999).
Li, J. & Yuen, D. A. Mid-mantle heterogeneities associated with Izanagi plate: implications for regional mantle viscosity. Earth Planet. Sci. Lett. 385, 137ā144 (2014).
Wu, J., Suppe, J., Lu, R. & Kanda, R. Philippine Sea and East Asian plate tectonics since 52āMa constrained by new subducted slab reconstruction methods. J. Geophys. Res. 121, 4670ā4741 (2016).
MĆ¼ller, R. D. et al. Ocean basin evolution and global-scale plate reorganization events since Pangea breakup. Annu. Rev. Earth Planet. Sci. 44, 107ā138 (2016).
Ballmer, M. D., Houser, C., Hernlund, J. W., Wentzcovitch, R. M. & Hirose, K. Persistence of strong silica-enriched domains in the Earthās lower mantle. Nat. Geosci. 10, 236ā240 (2017).
Tsujino, N. et al. Viscosity of bridgmanite determined by in situ stress and strain measurements in uniaxial deformation experiments. Sci. Adv. 8, eabm1821 (2022).
Rizo, H. et al. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809ā812 (2016).
Mukhopadhyay, S. Early differentiation and volatile accretion recorded in deep-mantle neon and xenon. Nature 486, 101ā104 (2012).
Liu, H., Leng, W., Wang, W. & Zheng, Y. Deciphering the deep Earth heterogeneities from the temperature fluctuation of mantle plumes. Earth Planet. Sci. Lett. 618, 118275 (2023).
Deng, Z. et al. Earthās evolving geodynamic regime recorded by titanium isotopes. Nature https://doi.org/10.1038/s41586-023-06304-0 (2023).
Smith, W. H. F. & Sandwell, D. T. Global seafloor topography from satellite altimetry and ship depth soundings. Science 277, 1957ā1962 (1997).
Engdahl, E. R., van der Hilst, R. & Buland, R. Global teleseismic earthquake relocation with improved travel times and procedures for depth determination. Bull. Seismol. Soc. Am. 88, 722ā743 (1998).
Shiobara, H., Baba, K., Utada, H. & Fukao, Y. Ocean bottom array probes stagnant slab beneath the Philippine Sea. EOS Trans. AGU 90, 70ā71 (2009).
Fan, J. et al. Seismic structure of the Caroline Plateau-Yap Trench collision zone. Geophys. Res. Lett. 49, e2022GL098017 (2022).
Kennett, B. & Engdahl, E. R. Traveltimes for global earthquake location and phase identification. Geophys. J. Int. 105, 429ā465 (1991).
Wang, J. & Zhao, D. P-wave anisotropic tomography beneath Northeast Japan. Phys. Earth Planet. Inter. 170, 115ā133 (2008).
Zhao, D., Hasegawa, A. & Kanamori, H. Deep structure of Japan subduction zone as derived from local, regional and teleseismic events. J. Geophys. Res. 99, 22313ā22329 (1994).
Laske, G., Masters, G., Ma, Z. & Pasyanos, M. Update on CRUST1.0āa 1-degree global model of Earthās CRUST. Geophys. Res. Abstr. 15, 2013ā2658 (2013).
Wright, C. & Kuo, B. Evidence for an elevated 410ākm discontinuity below the Luzon, Philippines region and transition zone properties using seismic stations in Taiwan and earthquake sources to the south. Earth Planets Space 59, 523ā539 (2007).
Paige, C. C. & Saunders, M. A. LSQR: an algorithm for sparse linear equations and sparse least squares. ACM Trans. Math. Software 8, 43ā71 (1982).
Zhao, D. Multiscale Seismic Tomography (Springer, 2015).
Acknowledgements
We used the high-quality waveform and arrival-time data provided by the International Seismological Centre (http://www.isc.ac.uk/isc-ehb/), the Ocean Hemisphere Project (http://ohpdmc.eri.u-tokyo.ac.jp), and the Oceanographic Data Center, Chinese Academy of Sciences (CASODC). We would like to thank all the scientists and crews of the research vessel KEXUE. We also appreciate Y. Hua, Q. Yan, J. Liao, L. Zhang and D. Peng for their constructive suggestions and comments. This work was financially supported by the National Natural Science Foundation of China under grants 41976052 and 42376080 to C.L. and D.D., 41876043 to J.F., 92355302 to L.L., the Strategic Priority Research Program of the Chinese Academy of Sciences under grant XDB42020102 and the Taishan Scholars Program under grant tsqn202312263 to J.F. and Japan Society for the Promotion of Science under grant 19H01996 to D.Z.
Author information
Authors and Affiliations
Contributions
J.F. and C.L. conceived this study. C.L. and D.D. collected the data and implemented data processing. D.Z. developed the tomographic codes. J.F. conducted the tomographic inversions. All authors contributed to the interpretations and preparations of the manuscript.
Corresponding authors
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature Geoscience thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editors: Alison Hunt and James Super, in collaboration with the Nature Geoscience team.
Additional information
Publisherās note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Supplementary Information
Supplementary Figs. 1ā29.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the articleās Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the articleās Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Fan, J., Zhao, D., Li, C. et al. Remnants of shifting early Cenozoic Pacific lower mantle flow imaged beneath the Philippine Sea Plate. Nat. Geosci. 17, 347ā352 (2024). https://doi.org/10.1038/s41561-024-01404-6
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41561-024-01404-6
This article is cited by
-
Remnants and fragments of the subducted paleo-Pacific plate: Constraints from geochemistry and geophysics
Science China Earth Sciences (2024)