Initial Opening Research Articles

Structural analysis of traditional Chinese puzzle boxes

Abstract. A puzzle box (also known as a trick box) is a box that may be opened by solving some obstacles originally designed by the manufacturer. Some puzzle boxes may be opened with a few moves, while others call for problem-solving and decision-making skills to unlock all the blocks inside the box. Puzzle boxes have existed throughout the ancient ages of the east and west, and their popularity has grown significantly since the 17th century. Chinese puzzle boxes are classified into four types based on the first movement during the initial opening stage: whole-box rotation, mechanical-member sliding, mechanical-member rotation, and pin removal. Since the topological structure of the puzzle box changes during the opening process, it falls under the category of the variable topology mechanism. This study proposes a graphical method for systematically analyzing traditional Chinese puzzle boxes. It discusses the structural characteristics of puzzle boxes and applies line graphs to explain the variable topological structures involved in the opening process. The paper presents four different types of puzzle boxes as examples of applying the proposed method and illustrating the opening processes of the puzzle boxes. Traditional Chinese puzzle boxes are diverse and creative, displaying the skilled craftsmanship of ancient artisans. A series of puzzle boxed can be further systematically synthesized through the atlas of line graphs and generalized chains.

Neoproterozoic basin evolution of the northern Tarim craton from back-arc rift to passive continental margin: Implications for the opening of the South Tianshan Ocean

The Neoproterozoic strata in the northern Tarim craton holds valuable tectono-sedimentary insights regarding the opening time and mechanisms of the South Tianshan Ocean, as well as the tectonic reconstruction of the Tarim craton during the breakup of Rodinia. However, debates remain around the Cryogenian–Ediacaran proto-basin type and evolution, as well as the lack of regional geological correlation at a basin scale. In this study, we employed seismic, drilling and outcrop data to conduct a combined tectono-stratigraphic and sedimentary filling analysis of the Cryogenian–Ediacaran strata in the northern Tarim craton, aiming to decipher the Neoproterozoic basin evolution. Our findings show that the deposition of the Cryogenian strata was controlled by normal faults, representing a rift basin receiving sedimentary materials from both the northern Tarim craton and the Central Tianshan block. In contrast, the Ediacaran developed as a depression basin featured by a wedge-shaped deposition with frequent sea-level fluctuations and simple detrital input from the northern Tarim craton, indicative of a passive margin basin. Such a Neoproterozoic basin evolution of the northern Tarim craton, from the Cryogenian rift to the Ediacaran passive margin, likely resulted from a back-arc extension due to the separation of the Central Tianshan arc from the Tarim craton. These results provide new constraints on the initial opening time of the South Tianshan Ocean at ca. 633 Ma and reveal the Neoproterozoic tectonic affinity of the Central Tianshan block and the northern Tarim craton. Our work also implies that the Tarim craton was located on the periphery of Rodinia, and the South Tianshan Ocean may not be a primary ocean basin of the Paleo-Asian Ocean.

A Novel Fast Contact Operating Mechanism of the Medium and Low Voltage Hybrid DC Current Limiting Circuit Breaker

In order to solve the problem of the slow initial speed caused by the large mass of the bistable permanent magnetic actuator (PMA) in the traditional bistable permanent magnetic–electromagnetic repulsion mechanism (PM-ERM), a novel fast contact operating mechanism is proposed by using the flexible spring system (SS) between the PMA and the ERM. The novel structure can separate the mass of the PMA and the ERM at the initial phase of the interrupting process, improve the initial speed of the contact and increase the initial opening distance of the contact. Firstly, the paper conducts an extensive investigation and analysis of the principle of the existing fast operating mechanism and points out the advantages and disadvantages of the existing mechanism. In order to meet the requirement of fast interrupting and improve the service life of the mechanism, a novel mechanism is proposed. And then, the working principle of the novel mechanism is introduced. The cooperative relationship between the ERM and the PMA and the working principle and performance parameter requirements of the ERM, SS and PMA are analyzed and designed. Finally, the feasibility of the novel mechanism is verified by the experiment. The results show that the opening distance of the novel operating mechanism can reach 2.25 mm in 1 ms. Compared with 1.24 mm of the traditional operating mechanism, it improves the initial opening distance of the contact by 81.5% and is conducive to the rapid interruption of the Hybrid DC current-limiting circuit breaker (HDCCLCB).

Antimicrobial efficacy of 2% chlorhexidine gel, triphala, and Azadirachta indica as intracanal medicaments against Enterococcus faecalis: A randomized clinical trial.

Concerns about adverse reactions and the development of antibiotic resistance have prompted an alternative treatment strategy that utilizes traditional medicinal herbs. This randomized control trial assessed the antimicrobial efficacy of 2% chlorhexidine (CHX) gel, Triphala, and Azadirachta indica as intracanal medicaments against Enterococcus faecalis. Forty patients with nonvital teeth and single root canals were selected (n = 10). Following the initial access opening, the first microbial samples (S1) were collected using paper points. Second microbial samples (S2) were collected following the chemo-mechanical preparation and 1 week after introducing the intracanal medicaments. Group I: 2% CHX, Group II: A. indica, Group III: Triphala, and Group IV: Calcium hydroxide (Ca(OH)2). S1 and S2 samples were collected, and bacterial growth was observed using the colony-forming unit (CFU) count. Comparison of the difference in CFU count among four groups was performed using one-way ANOVA test (P < 0.05) followed by post hoc Tukey test. Reduction in CFU count postmedication S2 from S1 in each group was statistically significant. Percentage reduction in CFU count was highest in Triphala group followed by A. indica and 2% CHX group. Percentage reduction in CFU count was least in Ca(OH)2 group. The post hoc pairwise comparison of % reduction in CFU count among four groups showed that the percent reduction was highest in Triphala group. Triphala has considerable antimicrobial efficacy against E. faecalis.

Intracranial pressure changes in traumatic brain injury patients undergoing unilateral decompressive craniectomy with dural expansion

BackgroundThe aim of this study is to assess the ICP changes induced by a unilateral fronto-temporo-parietal DC with dural expansion after moderate to severe TBI. The effect of different bone flap sizes on ICP and the neurological outcomes were also evaluated after the decompressive surgery. Methods52 TBI patients with clinical and radiological evidences of increased ICP were included in this prospective study. All patients received unilateral fronto-temporo-parietal DC with dural expansion and ventriculostomy at contralateral Kocher's point. Postoperatively, ICP values and the largest antero-posterior (AP) diameter of bone flap removed was measured, and the clinical outcomes were assessed using Extended Glasgow Outcome Scale (GOS-E) at discharge and 6 months after DC. ResultsThe median ICP significantly decreased with an average of 56.7 % reduction from the initial opening ICP. Similar ICP changes were observed in all groups. This study also found that the large bone flap group (AP diameter >15 cm) demonstrated better postoperative ICP control as compared to the small bone flap group (AP diameter 12–15 cm), although not statistically significant. The SDH and cerebral swelling groups did better in the GOS-E at 6 months after TBI compared with cerebral contusion group. ConclusionThe ICP reduction in moderate to severe TBI patients undergoing unilateral fronto-temporo-parietal DC with dural expansion occurred in accordance with decompressive steps, regardless of intracranial lesions and the surgical procedure should be performed with the bone flap size of at least 12 cm in AP diameter for adequate and sustained ICP control.

Exploring the impacts of high-speed rail on technology-intensive manufacturing: the case of the Yangtze River Delta region, 2007–2016

High-speed rail (HSR) may influence economic activities that rely heavily on innovation by facilitating skilled labour, face-to-face interactions, and knowledge spillovers. This study explores how HSR development affects the spatial distribution of technology-intensive manufacturing (TIM) in the Yangtze River Delta (YRD), China. Using a panel dataset including 24 cities for the period 2007–2016 and employing the output of communications equipment, computers, and other electronic equipment (CCOE) as a proxy for TIM’s economic productivity at the city level, we apply the staggered difference-in-differences (DID) and spatial Durbin model (SDM) to measure the impacts of HSR’s initial opening and connectivity on CCOE development and capture the spatial spillover effects of HSR connectivity. Our findings indicate that the initial opening of HSR and HSR connectivity are negatively associated with CCOE productivity in both DID and SDM. Additionally, the reduction of CCOE is more pronounced in cities with larger populations and higher levels of economy. Moreover, HSR has a more significant effect on CCOE than other manufacturing sectors. However, the spillover effects remain insignificant, indicating HSR’s limited impact on CCOE development in adjacent cities within the YRD.

Partisan bias in securities enforcement

Abstract In this article, I present a partisan theory of agency enforcement and empirically investigate the possibility of partisan bias in the enforcement of the federal securities laws. Leveraging plausibly exogenous shocks to partisan control of the U.S. Securities and Exchange Commission (SEC), I find evidence that a firm’s partisan alignment with the SEC substantially reduces the likelihood of enforcement. For a firm that is ex ante equally likely to be targeted for enforcement or not, my estimates indicate that a typical increase in partisan alignment following a change in party control of the SEC reduces the likelihood of enforcement by over 19%. Partisan alignment also appears to reduce aggregate monetary sanctions, though these estimates are less certain. By contrast, I find little evidence of partisan bias in the initial opening of investigations. These findings suggest there may be meaningful partisan bias in SEC enforcement and have important implications for democratic governance. (JEL D73, K22, K23, K41, K42, P00)

Mechanical and failure analysis of “outer single lap” adhesive joints of carbon fiber reinforced plastics under hygrothermal conditions

Carbon fiber reinforced plastics (CFRP)laminates are widely used in aircrafts. The laminates are often assembled into components by adhesive joints, which will be affected by elevated temperature and humidity during use, resulting in performance degradation. In this study, a compression test of “Outer Single Lap” adhesive joints of CFRP on the rear fuselage of a certain type of navigable aircraft was carried out to investigate the influence of hygrothermal conditions on their performance. The experimental environment includes the elevated temperature and wet condition (ETW) (71 °C, 85%RH) and Room temperature drying (RTD) (23 %, 30%RH). The test results show that RTD specimens have different stages, and the initial stage has good plasticity and no damage. However, when the load reached 50 %, the initial opening pattern damage occurred, which eventually led to the failure of the 20° opening. Compared with RTD samples, the compression properties of ETW samples decreased by 47.7 %, and the opening damage disappeared. Fracture features and stain analysis were performed. The findings suggest the fracture characteristic can change from a brittle fracture to a ductile fracture in different testing conditions, and the influence of the humid and thermal environment on the resin structural adhesive layer itself, the compression state of the carbon fiber laminates, the interface between the carbon fiber laminates and the resin structural adhesive layer should be fully considered in the design.

West Barents Sheared Margin Composite Tectono-Sedimentary Element, Norwegian–Greenland Sea and Fram Strait

The West Barents Sheared Margin developed in response to break-up and initial opening of the NE Atlantic and links to the Arctic Eurasia Basin. It consists of three first-order segments: (1) a southern sheared margin segment bounding the deep SW Barents Sea basins; (2) a central rifted margin segment west of Bjørnøya; and (3) a northern initially sheared margin segment that was later exposed to oblique extension west of Svalbard. The geometry of the margin included releasing, as well as restraining, bends that inflicted substantial impact on the deformation along the sheared margin. In light of structural, stratigraphic and sedimentological investigations in recent years, the first-order three-fold subdivision of the Barents shear margin has been strengthened and expanded on. It has become even clearer that this subdivision reflects the margin geometry and the shifting far-field and local stress configurations. Prior to the final stages of rifting and break-up of the NE Atlantic in the Paleogene, the study area was part of a broad and extensive basin province comprising deep sedimentary basins. The line of break-up cut diagonally across the regional basin province so that different parts of it are now located in the mid-Norwegian margin, in the NE Greenland margin and in the SW Barents Sea. These areas share a long and complex history of multiple rift phases throughout Late Paleozoic and Mesozoic times, and information from these areas is integrated into the description of the West Barents Sheared Margin Composite Tectono-Sedimentary Element. The marginal basins in the SW Barents Sea are the least explored area on the Norwegian continental shelf and sporadic exploration activity has had limited success. A petroleum potential still exist that will be elaborated in renewed upcoming activity.

Acoustic comfort improvement of simultaneous heating and cooling heat pumps using control logic for flow-induced noise reduction

Acoustic comfort in buildings can be achieved by minimizing unwanted noise generated primarily from heating, ventilation, and air-conditioning systems. However, research on noise reduction in simultaneous heating and cooling heat pumps (SHCHP) is limited. This study proposes a novel noise reduction control logic (NRCL) based on experiments on flow-induced noise through electronic expansion valves (EEVs) in an SHCHP. The flow-induced noise through EEVs was measured and analyzed regarding the degree of subcooling, differential pressure between indoor unit and evaporation (ΔPindoor), EEV opening speed (Vo), and opening (Oeev) while switching operation mode in an SHCHP. For all the operating and controllable variables, the peak sound pressure level (SPLpeak) was decreased by evenly distributing sound energy (SE). The sensitivity analysis indicated that Oeev and Vo were the most significant variables for achieving uniformly distributed SE. Therefore, a novel NRCL was proposed in terms of the initial EEV opening (Oeev,i) and dimensionless control time (CT) derived from the relationship between Oeev and Vo. The optimal CT for EEVs in SHCHP with NRCL was 1. At this point, the difference between SPLpeak and average SPL decreased by 46.2%, and the converging time for ΔPindoor to 0 increased by 17.8% compared with those of baseline.

LOAD-LOADING CAPACITY AND CRACK FORMATION OF REINFORCED CONCRETE CYLINDRICAL SHELL WHEN CHANGING ITS THICKNESS

The results of experimental studies of long cylindrical shells with the aim of determining their stress-strain state, load-bearing capacity and crack resistance when the thickness of the shell changes are described. A special stand was developed by the authors to implement the task. 4 models of a cylindrical shell made of reinforced concrete (samples RC1-RC4) were manufactured and tested. The thickness of the samples was 45, 50, 55, 60 mm, and the cross-sectional dimensions of the side elements were changed accordingly. The distributed load (vertical) was applied in four strips, each 13 cm wide, and only the body of the shell, i.e. the side members were not loaded. The shell hinges from the corners on 100x100mm plates. Inside each side element are two reinforcing rods with a diameter of 10 mm. In order to obtain a complete and reliable picture of the deformation of the shell surface, 4 hour-type indicators are attached to each of the three zones located between the load chains. In addition to indicators, strain gauges were pasted on the shell, which were used to monitor deformations on the upper and lower surfaces. The loading process ended when the tested shell lost its ability to resist the external load. The magnitude of the load corresponding to this moment was taken as the bearing capacity of the shell. Simultaneously with the shell samples, control samples of prisms and cubes were made to determine the physical and mechanical characteristics of concrete. Graphs of the dependence of the relative deformation on the load were constructed. The bearing capacity of the shells and the load at which the first crack formed were determined. By the time of loss of bearing capacity, cracks with the same initial opening width of 0.05 mm had formed in all shells. The final crack opening width, as well as the load-bearing capacity, slightly increased with increasing shell thickness. However, the load at the beginning of crack formation turned out to be the largest for the two average values of the shell thickness – 50 and 55 mm. The general pattern of cracking of all samples is almost the same. The test methodology and the developed stand are universal in nature and will be used for further research.

Intrusive mechanism of the 2018 Sierra Negra Galápagos eruption, constrained by 4D tomographic images

Understanding the mechanisms of magma intrusion underpins our ability to interpret geophysical monitoring signals at volcanoes and thus issue reliable forecasts of future activity. The basaltic caldera volcanoes of the western Galápagos Islands, Ecuador, exhibit exceptionally high rates of deformation driven by shallow magma accumulation and migration. However, the nature and evolution of magma storage at these volcanoes is poorly constrained by earthquake hypocentre locations or geodetic inversions. Here we show that transient variations in seismic velocity before, during, and after the 2018 eruption of the Sierra Negra volcano track the accumulation of magma in a shallow sill complex and the emplacement of a lateral flank intrusion. A four-dimensional tomographic technique applied to the P-wave arrivals of local earthquakes provides high spatiotemporal resolution of changes in the physical properties of the shallow volcanic system. In the month before the eruption, the expansion of a low-velocity zone above the sub-caldera sill complex coincides with caldera uplift and near-surface fracturing, driven by persistent shallow magma accumulation. A new low-velocity anomaly appeared progressively in the western flank of the volcano in the days after the onset of the eruption, coinciding with the opening of a curved sill that supplied magma to secondary eruptive fissures. The anomaly disappeared as the curved sill deflated after the initial opening, despite it remaining the conduit for magma from the caldera complex to the flank fissures. Low velocities across the shallow caldera after the end of the eruption likely result from rapid inflation due to recharge with fresh magma from depth. These results indicate a previously unknown complexity to the magmatic plumbing system at Sierra Negra and suggest velocity changes resulting from an interplay of thermal and stress perturbations.

Detrimental effects of scene manipulations on temperature-based time since death estimation

In forensic casework, time since death (TSD) estimations may play a crucial role to establish chains of events as well as for alibi assessment in homicide cases. Classical TSD estimation relies on reasonably stable ambient temperatures and a correct documentation of ambient and rectal temperatures. This constancy is in some cases disturbed by post-discovery alterations of the crime scene, e.g. opening a window. In order to develop a better understanding of this alteration-based detrimental impact on TSD estimation as well as to identify feasible recommendations for casework, the present pilot study examined ambient temperature effects of different window opening scenarios regarding various time intervals (5 to 360 min) in a furnished 10 m2 apartment during winter. In this context, in addition to the ambient temperature and thus the cooling rate of the room, re-approximation to initial room temperature, potential influences on a nomogram-based time since death estimation using a fictitious case, and the impact of the measurement height above the ground were investigated. Our data indicate a significant reduction of the mean temperature decrease rate after 15 min regardless of the remaining opening time and a correlation with the size of the respective opening surfaces. Re-approximation to initial room temperatures was observed with up to three times longer than the initial opening time. There was no evidence of a substantial advantage of temperature measurements above the level of the corpse (> 0.1 m). The limitations of the study and its applicability for forensic casework are critically reviewed.

A mixed trigger volumetric growth law for cylindrical deformation in stressed configurations

Soft tissue growth is crucial across various physiological applications, with mathematical modelling playing a pivotal role in understanding the underlying processes. The volumetric growth theory serves as a commonly used mathematical framework in this context. Our previous research on volumetric growth theory primarily concentrated on defining the incremental growth tensor in loaded and stressed configurations, revealing that this approach closely aligns with experimental observations of residual hoop stress distribution. However, given the assumptions employed, the approach has limitations in accurately predicting the growth timeline. In this work, we address these issues by incorporating the effect of initial residual strain and introducing a new mixed trigger growth evolution law. In this growth law, we do not use growth saturation as an upper limit, as this assumption cannot represent many physiological conditions. Instead, we propose that growth in soft tissues leads to a new equilibrium state. To illustrate this idea, we introduce a growth incompatibility function, denoted as I . We establish the analytical relationship between I and the opening angle in a simplified cylindrical geometry resembling the structure of the heart or arteries. We put forth a revised growth law that is both stress and incompatibility driven/Our results show that by using this mixed trigger growth law, tissues will not grow indefinitely. Instead, a stress-driven homeostasis incompatibility state will be reached. In addition, by accounting for the initial opening angle in the model, we can accurately trace the growth history of the heart, aligning with experimental data obtained from measuring the opening angle in young pigs from birth to maturity.

Catalytic mechanism of calcium ion on the NOx precursors formation during the pyrolysis of kitchen waste

Calcium ion (Ca2+) in kitchen waste exerts a significant impact on the formation of NOx precursors to affect the release of nitrogen oxides during the incineration process. However, the catalytic mechanism of Ca2+ is still unclear. Herein, 2,4-imidazolidinedione is employed as the nitrogen-containing model to study the effect of Ca2+ on the generation of NOx precursors during pyrolysis. Through density functional theory calculations (DFT) and wave function analysis of the catalytic effect of Ca2+, the results indicate that Ca2+ has different degrees of impact on the energy barriers of the initial ring opening reaction. Ca2+ not only changes the rate determining steps of NOx precursors formation pathways, but also reduces the total energy barriers formed by NH3. At the same time, the total energy barriers of all paths formed by HCN are raised. This work theoretically explains the phenomenon of Ca2+ promoting the formation of NH3, whereas inhibiting the release of HCN in pyrolysis experiments. In addition, Ca2+ promotes partial reaction pathways for the formation of HNCO, and the total energy barriers of catalytic pathways are lower than that of the uncatalyzed pathways. Therefore, under the catalysis of Ca2+, the generation pathway of HNCO is more competitive and it is conducive to the formation of HNCO.

Jet propulsion from a closing book

When a book closes, the air between the approaching surfaces is accelerated and ejected through the open sides at large speeds. The air resists this motion, and so a reaction forces acts on the closing book. To study this force, an idealized book is placed on rollers so it is free to move horizontally. The speed gained by the book is measured for different initial opening angles and for different book lengths. The dependence on these parameters is found to be surprisingly simple, and the extrapolation to plates of infinite length agrees well with a simple model. This system is interesting because it is relatively easy to build, measure, and model, and also because colliding surfaces in a fluid are an everyday occurrence. This system can be used as either a classroom demonstration or a laboratory experiment.

Influence of preoperative anatomy and functional status on outcomes after total temporomandibular joint replacement with patient-specific endoprostheses: A retrospective cohort study.

Temporomandibular joint (TMJ) replacement may be indicated for various pathological conditions, and the type of condition can affect the surgical procedure and outcomes. The causes of limited range of motion after alloplastic TMJ replacement have not been extensively studied. The present study aimed to evaluate the impact of preoperative jaw anatomy and functional status on the immediate and long-term outcomes of total TMJ replacement using a two-component patient-specific TMJ endoprosthesis. This retrospective study included 31 patients who underwent total TMJ replacement surgery between 2016 and 2020. The main outcome variable was the maximal incisal opening (MIO) after treatment. Secondary outcome variables included MIO improvement and the presence and type of postoperative complications. The primary predictive variable was the preoperative initial MIO. Secondary predictive variables included sex, age, indications for TMJ replacement, preoperative occlusion, condition of the glenoid fossa and/or condyle, shortening of the mandibular ramus, sagittal mandible position, lateral chin deviation, shape of the coronoid process, and type of surgery. The mean preoperative MIO was 13.0 ±8.0 mm, while the mean MIO 1 month after surgery was 20.6 ±5.5 mm, which was not statistically significant. However, at a later follow-up, functional parameters showed a significant improvement (p = 0.003), with a mean MIO of 32.5 ±5.0 mm 3 years after surgery. Statistical analysis indicated that the initial mouth opening is the strongest predictor of long-term functional recovery after TMJ replacement. Postoperative complications occurred in 4 cases (12.9%) following patient-specific endoprosthesis (PSE) placement. The use of PSEs for TMJ replacement has enabled the restoration of anatomical relationships in complex clinical cases and an improvement in mouth opening. The preoperative MIO was the only factor that significantly influenced long-term functional outcomes.

Early Triassic Volcanic Rocks in the Western Yarlung Zangbo Suture Zone: Implications for the Opening of the Neo‐Tethys Ocean

AbstractIn this study, zircon U‐Pb dating of volcanic rocks from the Zhongba ophiolite of the Yarlung Zangbo Suture Zone (YZSZ) in southern Xizang (Tibet) yielded an age of 247 ± 3 Ma. According to whole rock geochemical and Sr‐Nd‐Pb isotopic data, the Early Triassic samples could be divided into two groups: Group 1 with P‐MORB affinity, showing initial 87Sr/86Sr ratios of 0.70253–0.70602, εNd(t) values of 4.2–5.3, (206Pb/204Pb)t ratios of 16.353–18.222, (207Pb/204Pb)t ratios of 15.454–15.564, and (208Pb/204Pb)t ratios of 35.665–38.136; Group 2 with OIB affinity, showing initial 87Sr/86Sr ratios of 0.70249–0.70513, εNd(t) values of 4.4–4.9, (206Pb/204Pb)t ratios of 17.140–18.328, (207Pb/204Pb)t ratios of 15.491–15.575, and (208Pb/204Pb)t ratios of 36.051–38.247. Group 2 rocks formed by partial melting of the mantle source enriched by a former plume, and assimilated continental crustal material during melt ascension. The formation of Group 1 rocks corresponds to the mixing of OIB melts, with the same components as Group 2 and N‐MORBs. The Zhongba Early Triassic rocks belong to the continental margin type ophiolite and formed in the continental–oceanic transition zone during the initial opening of the Neo‐Tethys in southern Xizang (Tibet).

Refining the final phase of the seafloor spreading process in the West Philippine Basin through the recalibration of magnetic isochrones

The evolution of the West Philippine Basin (WPB), the largest back-arc basin in the northwestern Pacific margin, remains unclear, mainly due to the lack of accurate magnetic chronological constraints. We integrate a newly acquired shipborne magnetic grid and EMAG2 data to investigate the final phase of seafloor spreading and post-spreading magma-poor extension in the WPB during the Eocene and Oligocene. An ∼800 km-long transect located in the eastern part of the WPB was modeled to recalibrate the magnetic isochrones. The results show that the seafloor spreading direction of the WPB rotated counterclockwise from ∼NE–SW to ∼NNE–SSW at ∼44 Ma (Isochrone C20r) and from ∼NNE–SSW to ∼N–S at ∼39 Ma (Isochrone C18n.1n). After the latter rotation, the spreading became unstable, decreased significantly, fluctuated, and finally ceased at ∼33 Ma (Isochrone C13n). The post-spreading magma-poor extension along the Central Basin Rift (CBR) driven by the initial opening of the Parece Vela Basin (PVB) began ∼4 Myr after the cessation of spreading. In the area east of ∼132°E, the CBR inherited the fossil spreading center, but to the west, it manifests a newly formed rift valley intersecting the segmented fossil spreading center. The destabilization of the spreading process in the marginal basin during its extinction phase was predominantly controlled by the dynamic process and stress field imposed by the adjacent plate boundaries.

The Northeast Mindoro block is the conjugate margin of the southern East China Sea Basin: Insight from detrital zircon data

There is a hot debate over whether the initial opening of the South China Sea (SCS) took place in continental crust or oceanic crust. In this study, we present new detrital zircon U–Pb ages from late Eocene sedimentary rocks in the East China Sea Basin (ECSB). Our results reveal a broad U–Pb age spectrum with a substantial proportion of grains dating >1500 Ma. Notably, the provenance characteristics of the late Eocene ECSB are markedly distinct from other regions along the South China margin, as evidenced by kernel density estimation, nonmetric multidimensional scaling, and cumulative age distribution plots. The ECSB shared nearly identical provenance features with the northeast Mindoro block on the southern SCS margin during the late Eocene. Considering the previously proposed widespread breakup unconformity across the southern ECSB and the slab-based plate reconstruction from tomography of the SCS, we propose that northern Mindoro was the conjugate margin of the southern ECSB and underwent southward drifting during the SCS opening. This study provides a new plate reconstruction model of the SCS and evidence supporting the contention that the initial breakup of the SCS occurred within the continental crust.