Reconstruction Plate Research Articles

Unfolding rotational tectonics and topographic evolution from localized verses diffuse plate boundary counterparts

We present a kinematic model developed from geodetic observations, topography analysis and analogue tectonic modelling results, which reveals a striking similarity between the rotational tectonic settings of the Gakkel Ridge-Chersky Range system in the Arctic, and the Central Indian Tectonic Zone within the Indian subcontinent. A crucial aspect of large-scale extensional rift systems is the gradual variation of extension along the rift axis, due to plate rotation about a Euler pole, which may lead to contraction on the opposite side of the Euler pole to form a rotational tectonic system. Our geodetic and topographic analysis, combined with the reanalysis of analogue tectonic modelling results demonstrates such rotational tectonic plate motion in both the Arctic and Indian case. However, the plate boundary between the North American and Eurasian Plates as represented by the Arctic Gakkel Ridge-Chersky Range system is strongly localized, whereas the Central Indian Tectonic Zone that separates the North and South India Plates involves diffuse deformation instead. Furthermore, in both the Arctic and Central Indian we find that the relative Euler rotation pole is located near an indenter-like feature, which possibly controls the present-day rotational tectonics and contrasting topography on opposite sides of the Euler pole.

Solitary Intraosseous Neurofibroma of Mandible: Report of a Case

Neurofibroma is a benign tumor derived from the peripheral nerve. Most of these can be multifocal as a component of neurofibromatosis or present as a solitary tumor. Although the solitary neurofibroma is not an uncommon lesion, its intraosseous occurrence is rare, and less than 50 cases have been reported.
 We report a rare case of central neurofibroma, arising in the mandibular bone of 57-year-old edentulous female patient on the left side. Hemi mandibulectomy was performed and reconstructed with a reconstruction plate without any bone graft. Microscopic evaluation showed neoplastic tissue with haphazardly arranged and interlacing fascicular patterns composed of point-ended spindle-shaped tumoral cells. Immunohistochemical examination of the tumor showed positive staining for S-100 protein antibodies.

Anatomical study of the modified direct posterior gluteal splitting approach for acetabular fractures

BackgroundIn this study, we investigated the area that can be addressed with an approach in which the skin incision is made directly above the dorsal column with Thiel cadaveric specimens. MethodsSix Thiel cadaveric specimens were prepared. A skin incision was made directly above the dorsal column. The accessible proximal end from the proximal part of the greater sciatic notch to the gluteal ridge and the accessible distal end of the ischium were marked with a flat chisel. A molded 8-hole reconstruction plate was placed from the base of the ischium toward the gluteal ridge and fixed with 3 screws proximally and 2 screws distally. The length of the skin incision and the distance from each reference point on the bone to the reachable markings were assessed after the muscles were removed. ResultsMean skin incision length was 9.3 ± 0.7 (range, 8.0–10.0) cm. In 3 of 6 cases, proximal screws were inserted through different spaces between muscle fibers. In all cases, we were able to reach at least the greater sciatic notch, the gluteal ridge at the level of superior border of the acetabulum, and the base of the ischial tuberosity. In all cases, an 8-hole plate could be placed from the gluteal ridge to the base of the ischium. There were no superior gluteal artery or sciatic nerve injuries in any of the cases. ConclusionWe anatomically investigated the area that can be addressed with an approach in which the skin incision was made directly above the dorsal column. In all cases, we were able to access the areas needed to reduce the fracture and place the plates necessary to stabilize the fracture through a 9.3 ± 0.7 cm skin incision. This approach can be a useful minimally invasive posterior approach for acetabular fractures.

In-and-out Technique: An In-house Efficient Predictive Hole Fabrication Workflow

Summary: Virtual surgical planning (VSP) and three-dimensional (3D) printing can increase precision and reduce surgical time in craniofacial reconstruction. However, the elevated cost and manufacturing time of outsourced workflows is increasing the development of in-house solutions. One of the main challenges in in-house workflows is to create cutting guides that hold plate position information. This is due to the fact that hospitals usually lack the infrastructure required to design and 3D print custom-made plates. Including plate-positioning information in resection guides is especially relevant in complex reconstructions and when tumor extension limits plate placement before resection. Current in-house workflows revolve around the idea of 3D scanning the bent plate’s shape and to fuse it with the VSP. The goal of this article is to share our technique to transfer plate position information to resection guides. Our protocol uses a 3D model of the reconstruction as an intermediate step to transfer the plate position of a bent stock reconstruction plate to cutting guides. Two patients who required mandibular reconstruction with fibula flap are presented to illustrate the technique. This workflow requires a 3D-printed model of the desired outcome, cutting guides, and a stock plate. Results were satisfactory in terms of cutting location and angulation, plate adaptation and condylar position. This technique allows for a simple, safe, cheap, and quick alternative to add reconstruction plate information to cutting guides.

Linking Pacific Plate Motions to Metamorphism and Magmatism in Japan During Cretaceous to Paleogene Times

Plate reconstructions of oceanic domains are generally based on paleo-magnetic and seafloor spreading records. However, uncertainties associated with such reconstructions grow rapidly with increasing geological age because the original oceanic plates have been subducted. Here we synthesize advances in seismic tomographic mapping of subducted plates now lying within the mantle that assist plate reconstructions. Our proposed Japan–NW Pacific subduction histories incorporate tomography results and show three distinct stages comparable to those revealed by geochronology, petrology, and geochemistry. We propose major revisions to previously accepted ideas about the age, kinematics, and identity of the plates outboard of Japan during the Cretaceous–Paleogene Sanbagawa-Ryoke paired metamorphism. These revisions require updates to relevant plate convergence boundary conditions and thermo-dynamic models.

Comparison between mini-plate and reconstruction plate osteosynthesis in the treatment of the comminuted mandibular fracture.

Objective: To compare the treatment outcome for reconstruction plates and mini plates in treating comminuted mandibular fracture. Study Design: Randomized Controlled Trial. Setting: Department of Oral and Maxillofacial Surgery, Allama Iqbal Medical College/Jinnah Hospital, Lahore. Period: October 2021 to April 2023. Methods: All subjects presented for treatment of comminuted fractures of the mandible fulfilling the inclusion criteria at Jinnah Hospital Lahore Maxillofacial surgery department were included in the study, and were randomly allocated into group A and group B. The mini-plate osteosynthesis technique was used on Group A and Group B was treated by fixation with reconstruction plate. Results: A total of (n=30) patients were included in this study. Fifteen of these patients received mini-plate fixation (group A) and the remaining fifteen were treated with reconstruction plates (group B). The mean age was 29.4± 10.5 years. 80% of study subjects were male n=24. All patients of (group A) were treated via an intraoral approach. However, n=10 (66.6%) patients were treated by intraoral approach in (group B). Whereas the rest of the subjects (n=4) were treated with extra oral approach and (n=1) through combined intraoral and extra oral approach.100% stability at the fracture site was observed in both groups. Comparative occlusion status showed a nonsignificant p-value (p=1.000). Pearson chi-square value=0.0000a for plate exposure between both groups also shows a non-significant difference. The contour of the mandible was improved in 38.89% of (group A) population and 61.11% of group B patients. Conclusion: Mini-plate and reconstruction plate osteosynthesis are equally effective for the fixation of comminuted fractures of the mandible, considering postoperative occlusion status, stability of the fracture segment, and the possibility of plate exposure.

The end of the Cretaceous: depositional palaeogeographical reconstruction of the Gulf of Mexico and adjacent areas just prior to the Chicxulub impact

Abstract Until recently, information about the end of the Cretaceous was based upon investigation of global outcrop sections. New subsurface drilling and characterization from well cores and logs in the Gulf of Mexico Basin have greatly illuminated the end Cretaceous event. However, the palaeogeography of the late Maastrichtian just prior to bolide impact is less well understood and is of great importance in terms of modelling the resulting distribution and composition of the Chicxulub impact material, as well as tsunami and seiche wave height. Here, we examine the Maastrichtian strata in the basin, synthesizing lithostratigraphy and chronostratigraphy, tectonic plate reconstructions, global and local sea level history, palaeoclimate and depositional systems. Our new Maastrichtian palaeogeographical reconstruction shows the basin prior to the Chicxulub impact at a time of globally high sea level, with widespread deposition of deepwater chalks and shallow marine carbonates and local siliciclastic shorelines fed by the nascent Cordilleran belt. Stratigraphic correlations of wells and outcrops illustrate the range of palaeoenvironments from coastal plain to deep marine. As much as 610 m (2000 ft) of Maastrichtian and Campanian section is mapped around the basin, reflecting accommodation provided by basin subsidence, salt deflation and palaeophysiography. A large thickness of carbonates accumulated in the basin centre, with steep shoreline to basin gradients particularly in Mexico. At the end of the Cretaceous, carbonate palaeoenvironments probably covered 96% of the Gulf of Mexico Basin, with less than 4% of the area likely occupied by siliciclastic systems, a distribution that evolved from the Early Cretaceous. Our maps thus explain dominance of carbonate breccia and chalks in K–Pg boundary units deposited over the basin sites proximal or distal to the Chicxulub impact crater. This also elucidates the large impedance contrast and high amplitude seismic response of the K–Pg boundary horizon, mappable over vast portions of the basin.

Optimizing implant lattice design for large distal femur defects: Stimulating interface bone growth to enhance osseointegration

Large bone defects in the distal femur present a significant challenge due to the lack of inherent self-healing capabilities. Traditional approaches, such as utilizing polymethyl methacrylate (PMMA) in conjunction with a plate for distal femur reconstruction, have shown unsatisfactory osseointegration outcome, which leads to complications. To address this challenge, this study focuses on developing a lattice-structured implant for reconstructing distal femoral bone defects. The lattice geometry is based on the cuboctahedron lattice, with its design optimized through the adjustment of pillar diameter and arrangement angle. The lattice structure is designed to stimulate the surrounding bone, ultimately enhancing osseointegration in distal femur reconstruction. Finite element analysis revealed that for promoting bone ingrowth toward the implant, setting the optimal lattice structure parameters, i.e., a 45° arrangement angle and a 0.8 mm pillar diameter, is required. Fabricated using state-of-the-art metal three-dimensional printing, the implant underwent rigorous validation through biomechanical testing, in vitro biological assays, and animal experiments. The comprehensive results affirmed the bioactivity of the lattice-structured implant, underscoring its capability to improve osseointegration in distal femoral defect reconstruction.

THE USE OF PERIOSTEAL FLAP IN MANDIBLE PRIMARY RECONSTRUCTION AFTER SEGMENTAL RESECTION IN MEDICATION-RELATED OSTEONECROSIS PATIENT: CASE REPORT

Background: The treatment of medication-related osteonecrosis of the jaws is challenging. Mandible segmental resection is the main treatment method for advanced stage 2 and stage 3 medication- related osteonecrosis of the mandible. This brings to the large continuity defects of the mandible, decreasing the life quality of the patients. Method: In this study, a modified technique of mandible defect reconstruction, after segmental resection, with only a reconstruction plate, is described. In this technique, the periosteal flap is used for double-layer closure of the intraoral wound. Double-layer isolation of the reconstruction plate from the oral cavity prevents intraoral wound dehiscence and plate exposure. Also, for the bone fragments fixation, prebended 2.3mm reconstructive plate on the 3D-printed individual model of the patient’s mandible was used. The use of a prebended plate reduces the operation time and increases the precision of fixation of mandible fragments in the correct position. Results: After intraoral sutures removal on 14 days, there was a dehiscence of a few intraoral sutures on mucoperiosteal flaps. There was partial exposure of the periosteal flap, which secured the underlying reconstructive plate. Exposed periosteal flap spontaneously epithelialized during 1 month. The postoperative follow-up period was nine months. During this period no complications were noted Conclusion: Within the limitations of the study, this method can be used as an effective and predictable method for the primary reconstruction of the mandible with only a reconstruction plate in medication-related osteonecrosis of the jaws patients.

Modification of Archean cratons in southern Africa with foundered segments dropped into the shallow lower mantle

Abstract Subducted slabs have been detected in the lower mantle for almost 30 years, yet the presence of foundered cratonic segments in the lower mantle is still unclear and inadequately investigated. We present the first P-wave radial anisotropy tomography of southern Africa (our model SA-RAnis2024), which reveals a contrasting feature of preserved northwest and modified southeast Kalahari cratonic root. Segments from the modified cratonic lithosphere are inferred to have dropped into the shallow lower mantle where seismic evidence of isolated high-velocity anomalies are observed. We detect such a high-velocity anomaly under the southwest margin of the Kalahari craton, which possibly detached from the southeast Zimbabwe craton at ca. 60 Ma based on plate reconstructions. Foundered segments can be partially brought back up to shallow depths, and contribute to the geochemical heterogeneity of younger lithosphere, through large-scale mantle convection.

Functional reliability of means of fixation for complex pelvic fractures. Part 1: Materials and methods

Due to the military aggression of the Russian Federation against Ukraine, a large number of soldiers and civilians were wounded and injured. Along with fractures of the long bones of the limbs, skull injuries, limb amputations, the number of injuries in the pelvic area with fractures of the pelvic bones as a result of being hit by high-velocity projectiles (shrapnel, bullets) has increased.This work is devoted to the preparation and research of the characteristics of stiffness and reliability of fixation of complex fractures of the pelvic bones in the area of the sacroiliac joint and the upper and lower branches of the pubic bone, which may occur as a result of injury by high-velocity projectiles that injure.The sacroiliac area was fixed with two cancellous screws with a parallel arrangement at the intersection of the horizontal and vertical planes (a typical technique for stabilizing the posterior parts of the pelvis). The anterior parts of the pelvic bones were stabilized with rod devices of external fixation with a typical location of the rods in the upper anterior iliac spine. The upper branch of the pubic bone was synthesized with a bony reconstructive plate with a typical location.

Free iliac crest grafting technology for the management of critical-sized tibial bone defect

ObjectiveTo introduce the method and experience of treating critical-sized tibial bone defect by taking large iliac crest bone graft.MethodsFrom January 2020 to January 2022, iliac crest bone grafting was performed in 20 patients (10 men and 10 women) with critical-sized tibial bone defect. The mean length of bone defect was 13.59 ± 3.41. Bilateral iliac crest grafts were harvested, including the inner and outer plates of the iliac crest and iliac spine. The cortical bone screw was used to integrate two iliac bone blocks into one complex. Locking plate was used to fix the graft-host complex, supplemented with reconstruction plate to increase stability when necessary. Bone healing was evaluated by cortical bone fusion on radiographs at follow-up, iliac pain was assessed by VAS score, and lower limb function was assessed by ODI score. Complications were also taken into consideration.ResultsThe average follow-up time was 27.4 ± 5.6 (Range 24–33 months), the mean VAS score was 8.8 ± 1.9, the mean ODI score was 11.1 ± 1.8, and the number of cortical bone fusion in the bone graft area was 3.5 ± 0.5. Satisfactory fusion was obtained in all cases of iliac bone transplant-host site. No nonunion, shift or fracture was found in all cases. No infection and bone resorption were observed that need secondary surgery. One patient had dorsiflexion weakness of the great toe. Hypoesthesia of the dorsal foot was observed in 2 patients. Ankle stiffness and edema occurred in 3 patients. Complications were significantly improved by physical therapy and rehabilitation training.ConclusionFor the cases of critical-sized tibial bone defect, the treatment methods are various. In this paper, we have obtained satisfactory results by using large iliac bone graft to treat bone defect. This approach can not only restore the integrity of the tibia, but also obtain good stability with internal fixation, and operation skills are more acceptable for surgeons. Therefore, it provides an alternative surgical method for clinicians.

Real-time Reconstruction of Comminuted Mandibular Fractures Using 3D Printing.

Comminuted fractures of the jaws are complex injuries requiring special attention. In the past, treatment included closed reduction using maxillomandibular fixation. With advancements in technology and fixation systems, open reduction became a prevalent option. These fractures are difficult to reconstruct during the primary treatment phase, thus resulting in higher complication rates. The introduction of three-dimensional (3D) planning and printing brought about superior outcomes, yet these focus on secondary reconstruction due to the need for outsourcing planning and titanium printing. In this report, we describe real-time in-house 3D planning and printing using computer-assisted design software and a 3D-fused deposition printer for virtual reduction of the comminuted fractures and printing of the reconstructed mandible. Following virtual 3D reduction, the newly created mandibles were 3D printed. The model was then used to preband a reconstruction plate, which in turn was used as a template during surgery for reducing the segments. The process of virtual reduction and printing should take a couple of hours at most. The results of five cases showed good alignment and proper function. Three-dimensional technology can be applied in the everyday primary care treatment protocol of comminuted fractures as an in-house tool which greatly improves both functional and aesthetic outcomes.

Utilization of Polydioxanone Plate for Endoscopic Anterior Skull Base Repair: Operative Technique and Long-Term Cohort Outcomes

Abstract Objective The purpose of this study is to report the technical procedure and our experience using a polydioxanone suture (PDS) plate with dural substitute as part of a fully resorbable gasket seal technique to repair anterior skull base defects. Methods A series of patients undergoing anterior skull base reconstruction utilizing our resorbable gasket seal technique from January 2014 to July 2022 was reviewed. Results A total of 155 patients were included. Nine (5.8%) of the included patients developed postoperative cerebrospinal fluid (CSF) leaks requiring reoperation. There were no cases of intraoperative cranial nerve injury or internal carotid artery injury. A total of 103 (66.5%) patients were observed to have an intraoperative CSF leak, including 57 low-flow leaks and 46 high-flow leaks; 1 of 57 (1.8%) patients with low-flow leaks and 8 of 46 (17.4%) patients with high-flow leaks developed a postoperative CSF leak. During the first 3 years that this technique was utilized at our center for the management of high-flow intraoperative CSF leaks, postoperative CSF leaks were documented in 4 of 12 (33.3%) patients, in comparison to 4 of 34 (11.8%) in the following years. Conclusion PDS plate reconstruction confers several advantages and can be used in a diverse set of operative scenarios in conjunction with other reconstruction options. There appeared to be an associated learning curve as surgeons at our center gained experience with this new technique. Our findings show that the PDS plate reconstruction is safe and effective in repairing the skull base.

Changes in core–mantle boundary heat flux patterns throughout the supercontinent cycle

SUMMARY The Earth’s magnetic field is generated by a dynamo in the outer core and is crucial for shielding our planet from harmful radiation. Despite the established importance of the core–mantle boundary (CMB) heat flux as driver for the dynamo, open questions remain about how heat flux heterogeneities affect the magnetic field. Here, we explore the distribution of the CMB heat flux on Earth and its changes over time using compressible global 3-D mantle convection models in the geodynamic modelling software ASPECT. We discuss the use of the consistent boundary flux method as a tool to more accurately compute boundary heat fluxes in finite element simulations and the workflow to provide the computed heat flux patterns as boundary conditions in geodynamo simulations. Our models use a plate reconstruction throughout the last 1 billion years—encompassing the complete supercontinent cycle—to determine the location and sinking speed of subducted plates. The results show how mantle upwellings and downwellings create localized heat flux anomalies at the CMB that can vary drastically over Earth’s history and depend on the properties and evolution of the lowermost mantle as well as the surface subduction zone configuration. The distribution of hot and cold structures at the CMB changes throughout the supercontinent cycle in terms of location, shape and number, indicating that these structures fluctuate and might have looked very differently in Earth’s past. We estimate the resulting amplitude of spatial heat flux variations, expressed by the ratio of peak-to-peak amplitude to average heat flux, q*, to be at least 2. However, depending on the material properties and the adiabatic heat flux out of the core, q* can easily reach values >30. For a given set of material properties, q* generally varies by 30–50 per cent over time. Our results have implications for understanding the Earth’s thermal evolution and the stability of its magnetic field over geological timescales. They provide insights into the potential effects of the mantle on the magnetic field and pave the way for further exploring questions about the nucleation of the inner core and the past state of the lowermost mantle.

Complete Correction following Temporary Hemiepiphysiodesis using 2-hole Reconstruction Plates among Skeletally Immature Patients with Angular Deformities around Knees: A Descriptive Cross-sectional Study

Introduction: Studies have shown that 2-hole reconstruction plates can be used effectively as tension band plates for temporary hemiepiphysiodesis. However, limited data is available regarding the effectiveness of such plates in terms of complete correction rates. This study was aimed to find out the prevalence of complete correction following temporary hemiepiphysiodesis using 2-hole reconstruction plates among skeletally immature patients with angular deformities around knees. Methods: A descriptive cross-sectional study was carried out among skeletally immature patients with angular deformities around knees undergoing temporary hemiepiphysiodesis after getting approval from the Institutional Review Committee (Reference number: B&BIRC-23-05). The data were collected between 1 January 2012 to 31 December 2018. All skeletally immature patients with angular deformities around knees undergoing temporary hemiepiphysiodesis using 2-hole reconstruction plates were included. Patients who required additional procedures or implants for deformity correction and those who did not provide consent were excluded. Convenience sampling method was used. Point estimate at 95% Confidence Interval was calculated. Results: Among 102 patients, 66 (64.70%) patients achieved complete correction (59.97-69.43 at 95% Confidence Interval). Mean age of the patients was 8.21±3.11 years and 43 (65.15%) were males and 23 (34.84%) were females.Conclusions: The prevalence of complete correction following temporary hemiepiphysiodesis using 2-hole reconstruction plate among skeletally immature patients with angular deformities around knees was lower than that reported in other international studies.

The comparison between various methods of mandibular reconstruction based on finite element analysis.

The Mandible can be damaged by pathological factors, tumors, trauma, infection, and needs a surgical operation for reconstruction and restoring function. There are different methods for the reconstruction of mandible. Based on the surgical approach, primary reconstruction of mandible by reconstruction plate after resection is necessary for maintaining mandibular symmetric and esthetic of the lower third of the face. A finite element model of mandible and masticatory muscles was produced from a normal person (male with 35-year-old). The normal model was resected from the left sixth tooth to the second tooth. The pathological model was reconstructed in different conditions by macro plate. Different conditions were analyzed and compared based on bite force on right fifth tooth, stress developed on screws and macro plate. The finite element analysis results showed that maximum bite force and lower stress on screws were seen in the pathological model (condition 5) when one macro plate and six screws were inserted in the mid-body. The findings showed that the use of two macro plates causes lower stress on it than when we use one. Use of one macro plate and six screws is the best choice in mandibular immobilization which decrease the stress applied on bone and increase the bite force. Because of less stress developed on macro plates and screws, use of two macro plates or one macro plate in mid-body area are also preferred.

Development of a test bench for biomechanical simulation-a preliminary study of mandibular forces.

Purpose: The aim of this study is to develop a test bench, which integrates different complexity levels and enables in that way a flexible and dynamic testing for mid and long term intervals as well as testing of maximum loads till implant failure of different osteosynthesis systems on the mandible. Material and Methods: For this purpose, an analysis of the state of the art regarding existing test benches was combined with interviews of clinical experts to acquire a list of requirements. Based on these requirements a design for a modular test bench was developed. During the implementation of the test stand, functional tests were continuously carried out and improvements made. Depending on the level of complexity, the test bench can be used either as an incorporated variant or as a standalone solution. In order to verify the performance and the degree of fulfilment of the requirements of these two variants of the test bench, preliminary studies were carried out for all levels of complexity. In these preliminary studies, commercially available osteosynthesis and reconstruction plates were investigated for their biomechanical behaviour and compared with data from the literature. Results: In total, fourteen test runs were performed for the different levels of complexity. Firstly, five test runs were executed to test the simplified load scenario in the incorporated variant of the test bench. High forces could be transmitted without failure of the miniplates. Secondly a quasi-static test scenario was examined using the incorporated variant with simplified load insertion. Five experiments with a number of cycles between 40,896 and 100,000 cycles were carried out. In one case the quasi-static testing resulted in a fracture of the tested reconstruction plate with a failure mode similar to the clinical observations of failure. The last four test runs were carried out using the standalone variant of the test bench simulating complex load patterns via the insertion of forces through imitated muscles. During the test runs joint forces were measured and the amplitude and vector of the resulting joint forces were calculated for both temporomandibular joints. Differences in the force transmission depending on the implant system in comparison to the zero sample could be observed. Conclusion: The presented modular test bench showed to be applicable for examination of the biomechanical behavior of the mandible. It is characterized by the adjustability of the complexity regarding the load patterns and enables the subsequent integration of further sensor technologies. Follow-up studies are necessary to further qualify and optimize the test bench.

Long-lived Northern Hemisphere convergence systems driven by upper-mantle thermal inhomogeneity

Abstract Plate reconstructions reveal that two secular centers of convergence formed beneath eastern Eurasia and North America no later than 200 Ma. The cause of these convergence centers, which featured flat subduction, slab stagnation, and/or continental margin subduction, remains uncertain. Here, we propose that upper-mantle thermal inhomogeneity, particularly an anomalously cool Northern Hemispheric upper mantle, was a fundamental driver of this long-lived convergence. By considering the pattern of observed thermal inhomogeneity, our numerical models show that flow-induced asymmetrical subduction will tend to develop toward cold mantle domains, even when the subducting plate is buoyant. The models can reproduce the diverse subduction styles observed in the Northern Hemisphere by including proposed pre-subduction plate distributions and/or properties.

Initiation of the Cascade arc

Abstract The Cascade arc (western North America) is the world’s youngest continental arc, and because the down-going Juan de Fuca plate is young, it is also the hottest end member among subduction zones worldwide. We present evidence that the arc initiated <5 m.y. after accretion of the Siletzia oceanic terrane terminated the earlier subduction system and caused the northern portion of the Farallon slab to break off. Cascade magmatism began ca. 46 Ma with a new trench outboard of Siletzia, a reconfiguration commonly attributed to a seaward jump of the subduction zone. However, the presence of young buoyant oceanic lithosphere that would have resisted being forced into the mantle and the very rapid reestablishment of arc magmatism are hard to reconcile with initiation of a new subduction zone by this process. We propose an alternative mechanism in which the arc was reestablished as the intact southern portion of Farallon slab migrated northward from California (United States), converting a transform margin to a convergent one. This model utilizes plate reconstructions, petrology, mantle tomography, and geochronology to explain how subduction was initiated in a setting where the slab was young and hot and why the earliest Cascade magmatism occurred toward the middle rather than an end of the arc.