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Compositions of island arc and back-arc basin basalts are often used to trace the recycling of subducted materials. However, the contribution of subducted components to the mantle source during initial arc rifting before back-arc basin spreading is not yet well constrained. The northernmost Mariana arc is ideal for studying this because the transition from rifting to back-arc spreading is happening here. Here we report major and trace element and Pb isotopic compositions of olivine-hosted melt inclusions from lavas erupted during initial rifting at 24°N (NSP-24) and compare them with those in active arc front at 21°N and mature back-arc basin at 18°N. NSP-24 high-K melt inclusions have highly radiogenic Pb compositions and are close to those of the HIMU end-member, suggesting the presence of this component in the magma source. The HIMU-like component may be stored in the over-riding plate and released into arc magma with rifting. HIMU-type seamounts may be subducted elsewhere beneath the Mariana arc, but obvious HIMU-type components appear only in the initial stages of arc rifting due to the low melting degree and being consumed during the process of back-arc spreading. HIMU-type seamounts may be subducted elsewhere beneath the Mariana arc, but obvious HIMU-type components appear only in the initial stages of arc rifting due to the low melting degree and being consumed during the process of back-arc spreading.

Insight into the evolution of Philippine Sea‐South China Sea (SCS) plate motions helps reveal the driving mechanisms of the long‐term tectonic complexity in Southeast Asia. Here, based on the integration of the most recent geological and seismic data, we present a new plate reconstruction model for this region characterized by back‐arc extension and subduction since the Eocene. We suggest that the western boundary of the Philippine Sea Plate was a constant sinistral strike‐slip fault at 55–22 Ma with a clockwise self‐rotation. The connection between the SCS and Shikoku Ridges possibly initiates at 30 Ma, when their spreading times overlapped indicating an affinitive origin and magma source. Regional‐scale geodynamic simulations interfaced with our reconstructed plate motion indicate that the seismic high‐velocity body under the SCS is likely to be the leading edge of the Pacific Slab. Plain Language Summary Since 55 million years ago, East Asia has been going through a complex plate recombination. Several quantitative plate motion models have been published, but there remain several irrationalities, for example, a footwall plate was moving away from the trench. We established a new model for the Philippine Sea‐South China Sea (SCS) region as an improvement. Our model provides a smooth movement of the Philippine Sea Plate (PSP) from the equatorial zone to its present position, with a clockwise rotation. Based on it, we deduce: (a) the western boundary of the PSP was a sinistral strike‐slip fault; (b) the spreading ridges in SCS and Shikoku Basin were connected at 30 Ma; (c) the stagnant slab under the SCS is a part of the subducting Pacific Slab. Key Points A new plate reconstruction model of Philippine Sea‐South China Sea (SCS) region since 55 Ma by integrating the latest geological geophysical data The western boundary of the Philippine Sea Plate was a constant sinistral strike‐slip fault at 55–22 Ma The geodynamic model indicates the seismic high‐velocity body under the SCS likely to be the leading edge of the Pacific Slab

A rifted margin can be regarded, in the first place, as a crustal thinning taper framed by “box-shaped” continental and oceanic crusts whose top basement and Moho are parallel. Attempts to understand the relationship between lithosphere extension, crustal thinning and strain localization have been addressed in part by characterizing and modeling rift modes. However, a weakness of models stems from their using generalized physical parameters and initial conditions, while each system is unique in terms of its geological complexity. In this study, we develop a new approach to investigate the relation between crustal shape, the nature of the top basement and the accommodation space to reveal the link between extension, strain localization and crustal thinning in the northern South China Sea (N-SCS). Our results show the following: (1) box-shaped crusts may indicate no or minor extension, or extension compensated by crustal flow and/or magmatic additions; (2) crustal thinning and strain localization occurred through extensional detachment faults coevally during the rifting of the N-SCS; (3) strain localization was triggered or enhanced by magmatic weakening, and the weak crustal rheology at the onset of the rifting favored the formation of detachment faults; and (4) the inherited composition of the crust (magmatic rocks in the arc and meta-sediments in the forearc) controls the distribution of crustal thinning. We propose that the different initial conditions, changes in extension rates and the presence/absence of subduction dynamics account for the different rift evolutions observed in the SCS and Atlantic-type rift systems.

The Sturtian and Marinoan glaciations shaped Neoproterozoic palaeoenvironmental evolution. While methane emission likely intensified the Marinoan greenhouse effect, its role during the Sturtian glaciation—coinciding with widespread iron formations (IFs)—remains poorly understood. Here, we analysed bio-essential metals (Ni, Co, Zn), rare earth elements and yttrium (REY), Fe (δ 56 Fe) and Ni (δ 60 Ni) isotopes in hematite and magnetite, alongside bulk-rock and in-situ C isotopes of Mn-rich carbonates from five well-preserved Sturtian-aged IFs in South China. Our findings provide geochemical evidence for a methane-related biogeochemical pathway driving Fe-bearing mineral transformation via methanogenesis and metal-driven anaerobic methane oxidation (AOM), mediated by methanogens and anaerobic methane-oxidizing archaea (ANME) in ferruginous settings. Additionally, the Sturtian deglaciation facilitated atmospheric-oceanic O 2 exchange, increased nutrient influx from weathering, and methane release under slow AOM oxidation kinetics, potentially aiding ice sheet melting or prolonging glacial waning. Metal-driven anaerobic oxidation of methane and methanogenesis, mediated by a diverse microbial community, drove iron-mineral transformation and may have aided ice sheet melting, according to analysis of Sturtian iron formations from South China

Background To evaluate the feasibility and clinical effect of the suture anchor combined with external fixation in the treatment of the lateral femoral condyle Hoffa fracture. Methods In this study, a retrospective study was conducted to analyze the feasibility of treating fourteen patients (eight men and six women) with Hoffa fractures admitted to our Hospital from January 2016 to October 2021 with combined external fixation using incisional reduction anchor nailing. The age of the patients ranged from 23 to 45 years, with an average of 37.5 years. According to Letenneur’s classification, there were eight cases of type I, three cases of type II, and three cases of type III. The functional assessment of Letenneur was used to measure the clinical outcome. Results All patients had one-stage wound healing, and all patients were followed up for 12 to 18 months after surgery, and all fractures healed well, with normal knee flexion and extension activities, and no complications such as fracture displacement, anchor nail loosening, or fracture malunion were observed. The clinical outcome was evaluated according to the functional evaluation criteria of Letenneur et al. The clinical outcome of fourteen patients: excellent in thirteen cases and good in one case, with an overall excellent rate of 100%. Conclusions Our study results indicate that the use of anchor nailing combined with external fixation for Hoffa fractures of the femoral condyle has some clinical reference significance because it is less invasive, has fewer complications, does not require secondary removal, and is worthy of clinical application. Trial registration : Retrospectively registered.

Oceanic arc and back-arc magmas are typically sourced from mantle metasomatized by subducted slab fluids/melts, but the role of the overriding plate is often ignored. Here we report the oxygen isotopic compositions of olivines in basalts erupted during arc, arc rifting, and back-arc spreading stages in the Mariana convergent margin. Rifting-stage olivines have high Forsterite (Fo = 85–90) and mantle-like δ 18 O (4.92 to 5.69‰). The δ 18 O values of olivines in arc and back-arc basin lavas correlate with their Fo values; high-Fo (>83) olivines have mantle-like δ 18 O while those in low-Fo olivines are as low as 3.87 ± 0.30‰. This indicates that fractionating magmas assimilated low-δ 18 O oceanic crust in the hydrothermally-altered upper plate, rather than the injections of underlying subducted slab-derived melts. Considering the globally widespread distribution of low-δ 18 O evolved olivine, we propose that low-δ 18 O wall rock may be common in the shallow lithosphere and serves as an important contributor to erupted evolved magma. Fractionated magma in volcanic arcs assimilate upper plate hydrothermal altered oceanic crust wall rock with low oxygen isotopic signature, which contribute to the isotopic signature of erupted magma, according to geochemical and oxygen isotope data of olivine in basalt formed at the Mariana convergent margin.

We processed the raw multi-beam bathymetry data acquired in the central and northeastern part of the South China Sea by eliminating noise and abnormal water depth values caused by environmental factors, and a high resolution bathymetric map with a 20-m grid interval was constructed. Various scales of seafloor geomorphological features were identified from the data, including an image of Shenhu canyon, which is located in the northern continental margin of the South China Sea; submarine reticular dunes in the north of the Dongsha atoll; submarine parallel dunes in the northeast of the Dongsha atoll; and several seamounts in the southwest sub-basin and in the east sub-basin. In the processing step, various anomalies in the multi-beam bathymetry data were corrected. The optimal swath filtering and surface filtering methods were chosen for different scales of seafloor topography in order to restore the true geomorphological features. For the large-scale features with abrupt elevation changes, such as seamounts (heights of ~111–778 m) and submarine canyons (incision height of ~90–230 m), we applied swath filtering to remove noise from the full water depth range of the data, and then surface filtering to remove small noises in the local areas. For the reticular dunes and parallel dunes (heights of ~2–32 m), we applied only surface filtering to refine the data. Based on the geometries of the geomorphological features with different scales, the marine hydrodynamic conditions, and the regional structure in the local areas, we propose that the Shenhu submarine canyon was formed by turbidity current erosion during the Sag subsidence and the sediment collapse. The submarine reticular dunes in the north of the Dongsha atoll were built by the multi-direction dominant currents caused by the previously recognised internal solitary waves around the Dongsha atoll. The submarine parallel dunes in the northeast of the Dongsha atoll were built by the repeated washing of sediments with the influence of the tidal currents and internal solitary waves. The conical, linear and irregular seamounts identified from the bathymetry data were formed during the spreading of the southwest sub-basin and the east sub-basin. The identified seamounts in the multi-beam bathymetry data are correlated to deep magmatic activities, the Zhongnan transform fault and the NE-trending faults.

以阳江东凹及开平凹陷为研究对象，运用碎屑锆石U-Pb定年、地震剖面渠汇分析及沉积相分析等手段，系统分析文昌组和恩平组沉积期沉积物来源、输送渠道以及沉积形式，将“源-渠-汇”耦合的思想运用到珠江口盆地始新统沉积演化中。碎屑锆石U-Pb定年结果表明，研究区物源在时空上均表现出不均一性，文昌组阳江东凹碎屑锆石年龄以燕山期为主，年龄谱图表现为单峰值，开平凹陷则存在燕山期和印支期两个峰值，锆石自形程度均较好，指示盆内近源沉积；恩平组碎屑锆石年龄谱图均具有多峰值特征，且古生代和前寒武纪的锆石数量增多，锆石磨圆度高，说明开始接受盆外物源，为盆内和盆外双重供源。基于大量的地震剖面，在研究区分别识别出断槽、古沟谷及构造转换带等物源运输通道，阳江-一统暗沙断裂带的走滑作用对研究区始新统沉积物沿上述通道输送起到了重要作用。整体来讲，文昌组沉积期主要发育滨浅湖相、半深湖相和扇三角洲相，恩平组沉积期则主要发育辫状河三角洲相和滨浅湖相。本研究对于认识阳江东凹和开平凹陷始新统“源-渠-汇”过程以及阳江-一统暗沙断裂带在始新世的表现形式具有重要意义。

The tectonic evolution of the Caroline Plate during the Oligocene to Early Miocene was mainly controlled by two fulcrums. The west fulcrum at Palau Island remained fixed during 29–25 Ma as the Ayu Trough rifted and produced the abyssal hills parallel to its boundaries, and the Pacific Plate and part of the Caroline Plate subducted to the north. At the northeast corner of the Caroline Plate, the east fulcrum is surrounded by a series of arc seamount chains. These chains resulted from the convergence between the Caroline Plate and the Pacific Plate and crustal softening of the northeastern Caroline Plate induced by the Caroline Hotspot at ∼25 Ma. This softening of the crust also led to the dysfunction of the east fulcrum, and the west fulcrum migrated south, which caused dextral motion along the Ayu Rift and the development of an en echelon structure. The Yap Trench was a part of the spreading center in the Parece-Vela Rift at ∼29 Ma. However, sinistral motion along the Parece-Vela Rift at around 20–15 Ma led to the exposure of the subducted Yap Trench and left a triangular region with distinctive geophysical characteristics in the surrounding area.

The fields of structural geology and tectonics have witnessed great progress over the last decade and are poised for further expansion in the future. One of the significant breakthroughs is the establishment of the ＇Beyond Plate Tectonics Theory＇ where a combination of conceptual models and numerical modeling on plume tectonics and plate tectonics has enabled new insights into the structural and tectonic architecture and processes in the deep interior and deep sea. This paper synthesizes developments of structural geology and tectonics from a macroscopic perspective in deep interior and deep sea. Four key techniques are also reviewed： satellite altimetry for surface structures in deep-sea multi-beam sea-floor mapping; tomography for tectonics of the deep interior; diverse modeling approaches and software for unfolding dynamic evolution; and techniques for HT/HP experiments on material rheology and in situ component measurements.