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The closure of an ancient ocean basin via oceanic arc‐continent collision has two subduction styles with opposite polarities, which may proceed via subduction polarity reversal (SPR) or a subduction zone jump (SZJ). Interpreting the geometry or kinematic evolution of ancient collisional zones, especially the original subduction polarity, can be challenging. Here we used 2D thermo‐mechanical modeling to investigate the dynamic evolution process of SPR versus SZJ. Our modeling predicts different structural, topographic, magmatic, and basin histories for SPR and SZJ, which can be compared against, and help interpret, the geologic record past sites of oceanic closure during collisional orogens. Our results match geologic observations of past collisions in Kamchatka, eastern Russia, and the Banda Arc, eastern Indonesia, and thus our results can help effectively decode the evolutionary history of past arc‐continent collisions. Plain Language Summary: Determining the geometry and kinematic evolution of ancient subduction zones that experienced collision with an oceanic island arc can be challenging based on the surface geology along. Such collisions usually result in different dynamical evolution processes, namely subduction polarity reversal (SPR) or a subduction zone jump (SZJ). Here we conducted numerical modeling of oceanic island arcs that collide with a continental margin to explore the dynamic evolution process of different subduction styles. Our results reveal geologic indicators to decipher SPR versus SZJ in natural oceanic arc‐continent collisions, such as the distribution of thrust faults, metamorphic rocks, magmatism, crustal thickness, and topography. The numerical simulations help explain the geologic history of Kamchatka in eastern Russia and Banda Arc in eastern Indonesia. This study provides provide new insights and implications diagnosing the polarity of vanished subduction in arc‐continental systems. Key Points: New numerical models with convergent velocity boundary condition for deciphering subduction polarity during arc‐continent collisionsThrust faults, metamorphic rocks, magmatism, topography and Moho morphology can be used as indicators to diagnose subduction polarityThe evolution of subduction polarity reversal well explains the tectonic activities of the Kamchatka and Banda Arc in the Cenozoic [ABSTRACT FROM AUTHOR]

We investigated velocity and anisotropic structure of the crust beneath the eastern margin of the Tibetan Plateau to better understand its deformation and evolution mechanism. We performed H‐κ and Pms anisotropy analyses to obtain crustal thickness, Vp/Vs ratio, fast polarization direction, and splitting time from 711 stations, and further conducted quality control using slowness, harmonic and statistical analyses. The Songpan‐Ganzi Block has a large splitting time and a fast polarization direction roughly parallel to the GPS motion and SKS fast direction. It also shows an overall high but complex distribution of Vp/Vs ratio, and large variations in crustal thickness, indicating that crustal deformation is likely caused by crustal shortening and lower crustal flow. The northern Sichuan‐Yunnan Rhombic Block (SYRB) is featured by a thick crust and high Vp/Vs ratio, suggesting that the crust is likely inflated by partial melting lower crustal rocks. The subblock also exhibits a strong azimuthal anisotropy with a splitting time greater than 0.6 s. The fast polarization direction aligns with the nearly N‐S extended direction and rotates clockwise in front of the Emeishan Large Igneous Province (ELIP). The observed anisotropy agrees with aligned amphibole minerals under a simple shear condition, supporting a southward lower crust flow being diverted by the ELIP. Anisotropy measurements on the southern SYRB are less robust and widely scattered, suggesting a deformation mechanism different from the northern SYRB. In addition, the southeastern margin of the Sichuan Basin shows a systematic pattern of crustal anisotropy consistent with a pure shear deformation mechanism. Plain Language Summary: We studied the crustal structure and deformation beneath the eastern edge of the Tibetan Plateau. By analyzing teleseismic data from 727 stations, we measured crust thickness, Vp/Vs ratio, and azimuthal anisotropy using receiver functions. Our findings show a complex crustal behavior pattern in the eastern Tibet margin. In the Songpan‐Ganzi Block, crustal shortening and lower crust flow seem to be causing deformation. The northern Sichuan‐Yunnan Rhombic Block, with its thick crust and high Vp/Vs ratio, appears to be influenced by partial melting of lower crust rocks. And a southward lower crust flow being diverted by the Emeishan Large Igneous Province. The eastern and southern part of this block shows a different pattern, indicating a unique deformation mechanism. Additionally, the southeastern margin of the Sichuan Basin appears to undergo a distinct type of crustal deformation. Key Points: A new crustal model with much more reliable and denser Pms anisotropic measurements is built in the eastern Tibetan MarginSongpan‐Ganzi Block is likely deformed by crustal shortening and lower crustal flowChannel flow may exist in the west low velocity zone (LVZ) while absent at the east LVZ [ABSTRACT FROM AUTHOR]

The formation of a new ocean basin provides a unique observational window into the structure and deformation of the oceanic lithosphere. This study offers a detailed 1‐D vertically polarized shear‐wave velocity model of the young Japan Basin by interpreting S receiver functions, seafloor Rayleigh wave ellipticities and phase velocities in a Bayesian trans‐dimensional framework. The models suggest a distinct discontinuity in the mid‐lithosphere. Additional analyses indicate that the upper layer is characterized by strong positive radial anisotropy, while the lower layer is more isotropic. We interpret that the upper layer was formed during the back‐arc opening at 20–15 Ma, where the olivine lattice‐preferred orientation (LPO) fabric induced by passive upwelling contributes to the positive radial anisotropy. The lower, less anisotropic layer may be solidified after the sudden cessation of the opening. Small‐scale convection (SSC) from such a major tectonic event could randomize the LPO enough to weaken radial anisotropy before cooling down the asthenosphere, leaving a radially anisotropic discontinuity in the present‐day mid‐lithosphere. The proposed layered evolution history of the lithosphere beneath the Japan Basin illuminates an important role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Such an SSC‐induced radial anisotropy drop could also occur at the base of the lithosphere in regions with ongoing seafloor spreading and enhance the velocity drop of horizontally polarized shear waves. Thus, the role of SSC is non‐negligible in explaining the sharpness of the Gutenberg discontinuity detected by SS precursors beneath the oceanic lithosphere. Plain Language Summary: The formation of the oceanic lithosphere is associated with a relatively simple mantle convection process called seafloor spreading, but may also be affected by more complex, localized processes such as small‐scale mantle convection. To decipher the evolution history of the lithosphere of the Japan Basin, the Sea of Japan, this study collects earthquake waveforms from broadband ocean‐bottom seismometers and offers a detailed 1‐D seismic structural model beneath the Japan Basin by interpreting the multiple seismological observables in a trans‐dimensional Bayesian framework. Our seismic velocity model and associated analysis reveal that the oceanic lithosphere of the Japan Basin is seismically more complex than expected. The upper and lower parts of the lithosphere show distinct seismic anisotropy properties. We propose a layered evolution model for the lithosphere of the Japan Basin, in which small‐scale convection followed a normal seafloor spreading, and resulted in a structural discontinuity in the present‐day mid‐lithosphere. The proposed model highlights the role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Key Points: We construct detailed 1‐D Vsv models of the Japan Basin by trans‐dimensional inversion of multiple observables extracted from ocean‐bottom seismometers recordsOur analysis reveals a mid‐lithosphere discontinuity arising from strong positive radial anisotropy in the upper lithosphereA layered evolution mode associated with small‐scale convection is proposed for the lithosphere of the Japan Basin [ABSTRACT FROM AUTHOR]

In this study, a high‐resolution 3D lithospheric S wave velocity model of the Jiuyishan region is constructed by joint inversion of receiver function and ambient noise. Our Moho depth model reveals relatively thick crust (∼35 km) beneath the Yangtze block and thin crust (∼27 km) beneath the Cathaysia block. The model depicts a complex boundary between these blocks, roughly following the Chenzhou‐Linwu fault in the northern part but gradually curving westward in the southern part between the two blocks. The 3D S wave velocity model shows low‐velocity anomalies in the middle crust, as well as in the upper mantle, interpreted as evidence of asthenospheric upwellings in the upper mantle. These upwellings modify lithosphere structures by changing their temperatures and compositions, and may provide a heat source through the Chenzhou‐Linwu fault for the low‐velocity anomaly in the shallow part beneath Jiuyishan region. Plain Language Summary: The South China block, which is composed of the Yangtze and Cathaysia blocks, has undergone a series of intraplate orogenic episodes since the Neoproterozoic. Location of the southwestern boundary of the Yangtze and Cathaysia blocks has been ambiguous, and the local lithospheric structure is not well constrained. We construct a high‐resolution 3D lithospheric shear velocity model, which provides the first evidence suggesting that the Jiuyishan region is undergoing lithospheric modification. Our model depicts a complex boundary between these blocks, roughly following the Chenzhou‐Linwu fault in northern part but gradually curving westward in the southern part between the two blocks. Moreover, the shear wave velocity structure shows prominent low‐velocity anomalies in the middle crust as well as in the upper mantle. We interpret the low anomalies in mantle as asthenospheric upwellings, which may provide a heat source for the shallow low‐velocity anomaly. Key Points: High‐resolution lithospheric velocity structure as well as Moho depths in the Jiuyishan region are obtained from new seismic array dataBoundary between the Yangtze and Cathaysia blocks roughly follows the Chenzhou‐Linwu fault in the north but curves westward in the southThe asthenospheric upwellings beneath the Jiuyishan region may provide the heat source for a shallow low‐velocity anomaly [ABSTRACT FROM AUTHOR]

Situated in a transition zone between the western and eastern North China Craton (NCC), the central NCC exhibits complex dynamics features. Significant lithosphere thinning is observed beneath the eastern NCC and the northern segment of the central NCC. To study how the crust responses to the distinct lateral variations of the lithospheric mantle, we develop a method for joint inversion of Rayleigh and Love dispersion curves based on a transverse‐isotropic (or radial anisotropy) medium and obtain a 3‐D crustal radial anisotropy model. The results reveal significant heterogeneities along the Cenozoic Fenhe‐Weihe Rift (FWR). In the northern FWR, the discretely distributed lower crust positive anisotropy and upper crust negative anisotropy suggest the rifting is mainly dominated by the active mantle upwelling resulting in the Datong volcanoes. Similarly, the northern segment of the Taihang Mountain is also strongly affected by the magmatic activities and exhibits different anisotropy properties compared to its central‐to‐southern counterpart. Based on the negative anisotropy observed in the middle‐to‐lower crust beneath most parts of the Taihang Mountain, we speculate that a lower‐crust compression model can be applied to the Taihang Mountain, which is totally different to that of the adjacent Bohai Bay Basin. Possibly, the root of the Taihang Mountain is pushed by the westward moving lower crust coupled with the lateral escaping mantle flow beneath the Bohai Bay Basin. The Taihang Mountain and the Bohai Bay Basin are formed in similar tectonic environments, but are deformed in different ways. Key Points: A 3‐D crustal radial anisotropy model of the central North China Craton is builtMantle upwelling dominates the northern Fenhe‐Weihe Rift and northern Taihang MountainCrustal radial anisotropy evidences the lower‐crust compression beneath the southern the Taihang Mountain [ABSTRACT FROM AUTHOR]

The subduction flipping in the Taiwan region leads to complexities in the lithospheric structure. To better understand the arc‐continental collision process in this zone, we construct a 3‐D lithospheric model of the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc. In the middle to lower crust, low velocities are mainly located beneath the Ryukyu Trough and the rifted basins in the Taiwan Strait, and high velocities are imaged in the Kuanyin and Penghu Platforms. Likely, the Kuanyin and Penghu Platforms act as relatively strong barriers that block the persistent westward advance of the western deformation front of the Taiwan mountain belt, as manifested by shape of the deformation front that withdraws to the east in the basement highs. In the mantle, high velocities are observed beneath the Central Range and Ryukyu Arc, which is interpreted as the two oppositely oriented slab subductions, that is, subduction of the Philippine Sea slab in the northeast Taiwan and Eurasian slab subduction in south Taiwan. Based on the vertical transects through our 3‐D model, we find that the subduction polarity has flipped in north Taiwan, and the tectonic framework in central Taiwan is in the process of subduction polarity reversal. We also image significant low mantle velocities beneath the North Taiwan Volcanic Zone and Taihsi Basin, which may be related to the breakoff of the subducting Eurasian slab. In addition, we propose that the inherited weakness of the Taihsi Basin may have facilitated the slab breakoff in central Taiwan. Plain Language Summary: In this work we collect the seismic data recorded by seismic stations in and around the Taiwan orogen and build a high‐resolution lithospheric velocity model for an area including the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc by ambient noise tomography. The model exhibits low crust velocity anomalies in the Ryukyu Trough and rifted basins of the Taiwan Strait, and low velocities in the uppermost mantle beneath the North Taiwan Volcanic Zone and Taihsi Basin. Based on the tomographic images, we clearly find that the subduction polarity has been flipped in north Taiwan, and the tectonic framework in central Taiwan is in the process of subduction polarity reversal, which is in consistent with the geological observations. Key Points: A high‐resolution lithospheric model of the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc is obtained from ambient noise tomographySignificant low mantle velocities related to the breakoff of the subducting Eurasian slab are observed under the NTVZ and THBSubduction polarity reversal is ongoing in central Taiwan; the lithospheric scale weak THB facilitates the slab breakoff in central Taiwan [ABSTRACT FROM AUTHOR]

The Fenhe‐Weihe Rift (FWR) system is one of the most active rift zones in east China, and plays an important role in the reactivation of the North China Craton. In this work, a high‐resolution 3‐D lithospheric S wave velocity model of the FWR is built by joint inversion of receiver functions and ambient noise. Strong correlation between topography and tectonic features is observed at shallow depths. At great depths, strong heterogeneities are observed along the FWR: (1) high‐velocity anomalies emerge beneath the Weihe and Taiyuan basins in the lower crust; (2) two high‐velocity anomalies are imaged in the uppermost mantle beneath the south to central FWR; and (3) two strong large‐scale, low‐velocity zones are observed beneath the north Trans‐North China Oregon: one is at ~60 km and the other one is much larger with a deeper source. Based on the petrologic properties, geochemical analyses, and seismic images obtained in this work, we propose that the rifting mechanisms between the south and north FWR are different. In the south, the rifting could be mainly caused by the passive effects from the uplift of the Tibetan Plateau, while in the north the rifting is due to the combined effects of the asthenosphere upwelling and the counterclockwise rotation of the Ordos block. The uppermost mantle high‐velocity anomalies underneath the south to central part of the FWR could be the remnants of strong ancient cratonic root, and act as mechanical barriers to block the rifting processes between the south and north FWR. Plain Language Summary: A high‐resolution 3‐D crustal and uppermost mantle model of S wave velocity of the Fenhe‐Weihe Rift (FWR) is based on joint inversions of receiver functions and ambient noise. Two high‐velocity bodies are imaged in the uppermost mantle beneath the south to central FWR, while a large‐scale, low‐velocity zone was located beneath the north Trans‐North China Oregon. Passive rifting in the southern FWR is due to the uplift of the Tibetan Plateau, while rifting in the northern FWR is ascribed to the joint effects of the asthenosphere upwelling and propagation of the rifting from the south. Key Points: A high‐resolution 3‐D lithospheric S wave model of the FWR based on joint inversions of receiver functions and ambient noiseTwo high‐velocity bodies in the uppermost mantle beneath south to central FWR and a large‐scale, low‐velocity zone beneath the north TNCODifferent rifting mechanisms between the south and north FWR deciphered by the 3‐D seismic images in this work and previous evidences [ABSTRACT FROM AUTHOR]