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Pacific‐Panthalassa plate tectonics are the most challenging on Earth to reconstruct during the Mesozoic and Cenozoic eras due to extensive subduction, which has resulted in large (>9,000 km length) unconstrained gaps between the Pacific and Laurasia (now NE Asia) back to the Early Jurassic. We build four contrasted NW Pacific‐Panthalassa global plate reconstructions and assimilate their velocity fields into global geodynamic models. We compare our predicted present mantle structure, synthetic geoid and dynamic topography to Earth observations. P‐wave tomographic filtering of predicted mantle structures allows for more explicit comparisons to global tomography. Plate reconstructions that include intra‐oceanic subduction in NW Pacific‐Panthalassa fit better to the observed geoid and residual topography, challenging popular models of Andean‐style subduction along East Asia. Our geodynamic models predict significant SE‐ward lateral slab advections within the NW Pacific basin lower mantle (∼2,500 km from Mesozoic times to present) that would confound “vertical slab sinking”‐style restorations of imaged slabs and past subduction zone locations. Plain Language Summary Our knowledge of Earth's past tectonic plate configurations becomes increasingly uncertain going back into geologic time. Northwest Pacific‐Panthalassa plate tectonics along East Asia and the northern Pacific margin are among the most uncertain place on Earth to reconstruct during the Mesozoic‐Cenozoic eras. Numerous hypotheses have been proposed: one popular hypothesis suggests a large oceanic plate subducted continuously and exclusively under the eastern margin of Asia throughout Jurassic and Cretaceous times (i.e., Andean‐type subduction); a second hypothesis assumes that a number of smaller plates existed within the Northwestern Pacific that subducted both under the Asian margin and at offshore subduction zones (i.e., intra‐oceanic subduction). Using numerical models of mantle convection, we computed where each hypothesis predicts the subducted lithospheric plates to be at present in the Earth's interior. We compared these predictions against tomographic images of the Earth's mantle. We also calculated the gravitational attraction caused by the predicted mass distributions and compared them against the observed geoid. The warping of the Earth's surface caused by mantle flow was also computed and compared against non‐hydrostatic topography measurements. Our results favor plate reconstructions featuring intra‐oceanic subduction within Northwestern Pacific‐Panthalassa, with implications for past global CO2 and reconstructing disappeared ocean basins. Key Points Six fully kinematic, end‐member western Pacific plate tectonic reconstructions were assimilated into global geodynamic models Intra‐oceanic subduction in western Pacific produces synthetic geoid and dynamic topography best fit observed geoid and residual topography Geodynamic models predict significant SE‐ward lateral slab advections within NW Pacific lower mantle (∼2,500 km from Jurassic to present)

Geothermal heat flow is a key parameter in governing ice dynamics, via its influence on basal melt and sliding, englacial rheology, and erosion. It is expected to exhibit significant lateral variability across Antarctica. Despite this, surface heat flow derived from Earth's interior remains one of the most poorly constrained parameters controlling ice sheet evolution. To obtain a continent‐wide map of Antarctic heat supply at regional‐scale resolution, we estimate upper mantle thermomechanical structure directly from VS. Until now, direct inferences of Antarctic heat supply have assumed constant crustal composition. Here, we explore a range of crustal conductivity and radiogenic heat production values by fitting thermodynamically self‐consistent geotherms to their seismically inferred counterparts. Independent estimates of crustal conductivity derived from VP are integrated to break an observed trade‐off between crustal parameters, allowing us to infer Antarctic geothermal heat flow and its associated uncertainty. Plain Language Summary The future evolution of the Antarctic Ice Sheet depends on its stability, which describes how sensitive it is to environmental change. A key factor influencing ice sheet stability is how much thermal energy is transferred into its base from Earth's interior: a parameter called geothermal heat flow. If the level of heat supply is high, melting at the base of the ice sheet is encouraged, resulting in enhanced sliding toward outlet glaciers at the continental perimeter. Consequently, ice loss is accelerated, and the likelihood of glacial collapse is increased. Therefore, an accurate map of Antarctic geothermal heat flow, including how this parameter varies from region to region, is needed to produce high quality projections of Antarctic ice mass loss and therefore global sea level change. In this study, we use models of how seismic wave speed varies within Earth to estimate its three‐dimensional temperature structure, as well as its thermal conductivity. These data are used to infer a collection of best‐fitting models of Earth's thermal state, and hence estimate Antarctic geothermal heat flow. Key Points Demonstration of new methodology for inferring geothermal heat flow from seismological data S‐ and P‐wave velocity used together to infer and fit geotherms Incorporation of laterally varying crustal conductivity and heat production

Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., superplumes) and circum‐Pacific seismically fast anomalies (i.e., a globally spherical harmonic degree 2 structure). However, the cause for and time evolution of the African and Pacific superplumes and the degree 2 mantle structure remain poorly understood with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Myr and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma) and the mantle in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree 1 structure before the Pangea formation). Here, we construct a proxy model of plate motions for the African hemisphere for the last 450 Myr since the Early Paleozoic using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations. Coupled with assumed oceanic plate motions for the Pacific hemisphere, this proxy model for the plate motion history is used as time‐dependent surface boundary condition in three‐dimensional spherical models of thermochemical mantle convection to study the evolution of mantle structure, particularly the African mantle structure, since the Early Paleozoic. Our model calculations reproduce well the present‐day mantle structure including the African and Pacific superplumes and generally support the second proposal with a dynamic cause for the superplume structure. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ∼230 Ma (i.e., ∼100 Myr after the assembly of Pangea). Particularly, the last 120 Myr plate motion plays an important role in generating the African superplume. Our models have implications for understanding the global‐scale magmatism, tectonics, mantle dynamics, and thermal evolution history for the Earth since the Early Paleozoic.

MgFe2O4 was probed to 74(1) GPa and 2,840(130) K as a low‐pressure analog to post‐post spinel Mg2SiO4 predicted in super‐Earths using synchrotron multigrain X‐ray diffraction techniques in the laser‐heated diamond anvil cell. With high‐temperatures above 65 GPa the eight‐fold coordinated δ‐MgFe2O4 (Th3P4‐type) is stable with Mg and Fe disordered into one site, analogous to that predicted in Mg2SiO4. While the phase‐boundary slope between the h‐ and δ‐phases of MgFe2O4 and Fe3O4 differ, the substitution of Fe2+ and Mg2+ has little overall pressure effect on the stability of the post‐post spinel phase. This eight‐fold coordinated δ‐MgFe2O4 is stable at ∼400 GPa lower pressures compared to the predicted δ‐Mg2SiO4, suggesting the need for further explorations into the conditions needed to substitute Fe3+ into δ‐Mg2SiO4 and the effect of ferric iron on the onset of eight‐fold coordination in super‐Earth mantles.

The southwestern United States hosts well‐documented and dramatic variations in topography, seismicity, heat flow, magmatism, and seismic velocity structure. This region offers opportunities to investigate how processes such as temperature and partial melt are related to the Lithosphere‐Asthenosphere Boundary (LAB), and how they ultimately shape lithospheric evolution. Using interpretive toolkits and a seismic wavespeed model that offers new high‐resolution constraints on upper mantle absolute velocities and gradients, we model the thermal structure and melt fraction throughout the upper mantle in the southwestern United States, with an emphasis on resolving the LAB. In the northern interior of the Colorado Plateau and in the Wyoming Craton, the LAB (as defined from the thermal models) is relatively deep and upper‐mantle melt is not likely. In the Basin and Range and southern Colorado Plateau, in contrast, the lithosphere is thin, and temperature is near the solidus in the upper mantle. Small fractions of partial melt are potentially stable in the asthenosphere over large tracts of the Basin and Range, and within the southern margin of the Colorado Plateau. Furthermore, the best‐fit thermal models are consistent with a transition layer between the lithosphere and asthenosphere, in which temperatures exceed the solidus. Such a scenario could be accommodated by small‐scale irregularities in LAB depth and/or channelized melt infiltrating the lithosphere. This work underscores the sensitivity of modeled melt to volatile content, and the significant consequences of melt stability on the long‐term evolution of the lithospheric mantle.

The Tethyan evolution depicts the continuous process of landmasses separating from the Gondwana continent in the south, drifting northwards, and subsequently colliding with the continents in the north over the past 500 million years. In this process, the Tethyan oceans that formed between the landmass and the southern or northern continents underwent growth, evolution, and eventual closure with the early Cenozoic India-Eurasia collision. However, the Tethyan lithosphere did not disappear but rather continued to evolve after entering into the deep Earth. The current position, morphology, and volume of the subducted Tethyan oceanic slabs in the deep mantle record the latest moment of this continuous evolution, providing critical constraints for Tethyan studies. This paper summarizes and analyzes the results of global-scale whole-mantle seismic tomography in the past nearly two decades, revealing a northwest-southeast seismically high-velocity anomaly, which is linearly distributed at depths of 1000–2000 km beneath the Tethyan realm and referred to as the Tethyan anomaly. By searching for an optimal linear combination of previous global seismic tomographic models to best match the known subducted slabs in the upper mantle, we observe that the Tethyan anomaly extends approximately 8700 km in length and 2600 km in width, exhibiting a parallel structure with northern and southern branches. Combining geological records of oceanic subduction initiation and previous geodynamic studies, this study suggests that the main body of the Tethyan anomaly represents the remnants of the subducted Neo-Tethyan oceanic slabs, which subducted from the Late Jurassic to the early Cenozoic. The northern branch consists of subducted slabs from the Neo-Tethys beneath the southern margin of Eurasia, while the southern branch likely reflects the intra-oceanic subducted slabs of Neo-Tethys during the Cretaceous. The western portion of the Tethyan anomaly may reflect remnants of Paleo-Tethys, while the eastern portion, towards India and the Bay of Bengal, shows signs of subduction towards the core-mantle boundary. Finally, this study discusses the future prospects of whole-mantle seismic tomographic studies focusing on the Tethyan realm.

The geochemical study of the Earth＇s mantle provides important constraints on our understanding of the formation and evolution of Earth, its internal structure, and the mantle dynamics. The bulk Earth composition is inferred by comparing terrestrial mantle rocks with chondrites, which leads to the chondritic Earth model. That is, Earth has the same relative proportions of refractory elements as that in chondrites, but it is depleted in volatiles. Ocean island basalts （OIB） may be produced by mantle plumes with possible deep origins; consequently, they provide unique opportunity to study the deep Earth. Isotopic variations within OIB can be described using a limited number of mantle endmembers, such as EM1, EM2 and HIMU, and they have been used to decipher important mantle processes. Introduction of crustal material into the deep mantle via subduction and delamination is important in generating mantle heterogeneity; however, there is active debate on how they were sampled by mantle melting, i.e., the role of olivine-poor lithologies in the OIB petrogenesis. The origin and location of high 3He/4He mantle remain controversial, ranging from unprocessed （or less processed） primitive material in the lower mantle to highly processed materials with shallow origins, including ancient melting residues, mafic cumulates under arcs, and recycled hydrous minerals. Possible core-mantle interaction was hypothesized to introduce distinctive geochemical signatures such as radiogenic 186Os and Fe and Ni enrichment in the OIB. Small but important variations in some short-lived nuclides, including 142Nd, 182W and several Xe isotopes, have been reported in ancient and modern terrestrial rocks, implying that the Earth＇s mantle must have been differentiated within the first 100 Myr of its formation, and the mantle is not efficiently homogenized by mantle convection.

This is a survey of mantle provinces (large‐scale seismic anomalies) under North America, from the surface down to 1500–1800 km depth. The underlying P velocity model was obtained by multifrequency tomography, a waveform‐based method that systematically measures and models the frequency‐dependence of teleseismic body waves. A novel kind of three‐dimensional rendering technique is used to make the considerable structural complexities under North America accessible. In the transition zone and below, the North American mantle is dominated by seismically fast provinces, which represent distinct subduction episodes of the Farallon plate. I attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes. Differences in vertical sinking velocity have led to large vertical offsets across adjacent, coeval slabs. Some of the mantle provinces have not been discussed much previously, including (1) a seismically slow blanket overlying the oldest Farallon subduction along the eastern continental margin, (2) a transition zone slab coeval with the Laramide orogeny (ca. 80–60 Myr), which I discuss in analogy to the “stagnant slab” subduction style commonly found in the western Pacific today, (3) the lower mantle root of present‐day Cascadia subduction, which may have started out as intraoceanic subduction,(4) a lower mantle slab under Arizona and New Mexico, the last material to subduct before strike‐slip motion developed along the San Andreas boundary, and (5) two narrow plate tears thousands of kilometers long, one of which is the subducted conjugate of the Mendocino Fracture Zone.

The oldest oceanic basin (160–180 Ma) in the western Pacific is the birthplace of the Pacific Plate and is thus essential for understanding the formation and evolution of the oceanic plate. However, the upper mantle structure beneath the region has not been thoroughly investigated because of the remoteness and difficulties of long‐term in situ seismic measurements at the ocean bottom. From 2018 to 2019, the Oldest‐1 experiment on the oldest seafloor was conducted as part of the international Pacific Array initiative. We present the first three‐dimensional P ‐wave velocity structure down to a depth of 350 km based on the relative travel time residuals of teleseismic earthquakes recorded by 11 broadband ocean‐bottom seismometers operated during the Oldest‐1 experiment. Our result shows a fast P ‐wave velocity anomaly ( V P perturbation of 2%–4% faster than average) at a depth of 95–185 km beneath the northeast of the study area. This structure is interpreted as evidence of dry, viscous, and rigid materials at depths below the lithosphere. Two slow anomalies ( V P perturbation of 2%–4% slower than average) are seen beneath the southwestern and eastern (the oldest seafloor >170 Ma) parts of the array site. The low‐velocity zones are found at depths of 95–305 km. The observed velocity structures can be indicative of plume activities that affected the upper mantle as the Pacific Plate migrated over hotspots from the southeast. Alternatively, the observed velocity features may provide seismic evidence for small‐scale sublithospheric convection. One‐year ocean‐bottom geophysical investigation on the oldest Pacific provides seismic mantle structure of the region Detailed 3‐D mantle structure implies complex evolution process of Pacific Plate Our model implies thermochemical modification of the upper mantle by plume interaction or small‐scale convection

Mantle tomography reveals the existence of two large low-shear-velocity provinces (LLSVPs) at the base of the mantle. We examine here the hypothesis that they are piles of oceanic crust that have steadily accumulated and warmed over billions of years. We use existing global geodynamic models in which dense oceanic crust forms at divergent plate boundaries and subducts at convergent ones. The model suite covers the predicted density range for oceanic crust over lower mantle conditions. To meaningfully compare our geodynamic models to tomographic structures, we convert them into models of seismic wavespeed and explicitly account for the limited resolving power of tomography. Our results demonstrate that long-term recycling of dense oceanic crust naturally leads to the formation of thermochemical piles with seismic characteristics similar to the LLSVPs. The extent to which oceanic crust contributes to the LLSVPs depends upon its density in the lower mantle for which accurate data is lacking. We find that the LLSVPs are not composed solely of oceanic crust. Rather, they are basalt rich at their base (bottom 100–200 km) and grade into peridotite toward their sides and top with the strength of their seismic signature arising from the dominant role of temperature. We conclude that recycling of oceanic crust, if sufficiently dense, has a strong influence on the thermal and chemical evolution of Earth’s mantle.