The evolution of basal mantle structure in response to supercontinent aggregation and dispersal

Seismic studies have revealed two Large Low-Shear Velocity Provinces (LLSVPs) in the lowermost mantle. Whether these structures remain stable over time or evolve through supercontinent cycles is debated. Here we analyze a recently published mantle flow model constrained by a synthetic plate motion model extending back to one billion years ago, to investigate how the mantle evolves in response to changing plate configurations. Our model predicts that sinking slabs segment the basal thermochemical structure below an assembling supercontinent, and that this structure eventually becomes unified due to slab push from circum-supercontinental subduction. In contrast, the basal thermochemical structure below the superocean is generally coherent due to the persistence of a superocean in our imposed plate reconstruction. The two antipodal basal thermochemical structures exchange material several times when part of one of the structures is carved out and merged with the other one, similarly to “exotic” tectonic terranes. Plumes mostly rise from thick basal thermochemical structures and in some instances migrate from the edges towards the interior of basal thermochemical structures due to slab push. Our results suggest that the topography of basal structures and distribution of plumes change over time due to the changing subduction network over supercontinent cycles.

COMPLICATIONS OF RECONSTRUCTION PLATE INSTALLATION IN MANDIBULAR

Background: Mandibular resection will cause mandibular stability disturbance due to loss of some part of the bone. Instability of the mandible can cause aesthetic, physiological, and psychological malfunction. Installment of mandibular reconstruction plat on the remaining mandibular using screws were suggested to restore its stability. However, it is not uncommon that plat exposure occurs following mandibular reconstruction, caused by inaccurate adaptation of the plats to the mandibular bone. The aims of this report are to describe the various complications and managements after jaw resection and reconstruction with plates. Case Report: A 44 years old male patient complained the small defect in the chin, painless, and no fluid emited, accompanied by dermatitis. Intra oral examination showed no abnormalities. About 1 year ago the patient performed segmental resection of the mandible on the indication of ameloblastoma. The radiological x-ray showed all screw detached from the plat and radiolucent images appeared around the plat that attached to the mandible. The diagnosis was fistula at regio mentale, post resection and reconstruction surgery, suspected caused by titanium plate allergies. The provided therapies were fistulectomy, screw removal, and plate reconstruction. Post therapy conditions showed improvement and no patients complaints of pain. Conclusion: Plate exposure is a complication that can occur after the installation of the reconstruction plate, but besides that it can also cause an allergic reaction from the material used. Keywords: Complication, Mandibular Resection, Plate Reconstruction, Titanium Plate Allergies

Subduction history of the Caribbean from upper-mantle seismic imaging and plate reconstruction

The margins of the Caribbean and associated hazards and resources have been shaped by a poorly understood history of subduction. Using new data, we improve teleseismic P-wave imaging of the eastern Caribbean upper mantle and compare identified subducted-plate fragments with trench locations predicted from plate reconstruction. This shows that material at 700–1200 km depth below South America derives from 90–115 Myr old westward subduction, initiated prior to Caribbean Large-Igneous-Province volcanism. At shallower depths, an accumulation of subducted material is attributed to Great Arc of the Caribbean subduction as it evolved over the past 70 Ma. We interpret gaps in these subducted-plate anomalies as: a plate window and tear along the subducted Proto-Caribbean ridge; tearing along subducted fracture zones, and subduction of a volatile-rich boundary between Proto-Caribbean and Atlantic domains. Phases of back-arc spreading and arc jumps correlate with changes in age, and hence buoyancy, of the subducting plate.

East Antarctica magnetically linked to its ancient neighbours in Gondwana

We present a new magnetic compilation for Central Gondwana conformed to a recent satellite magnetic model (LCS-1) with the help of an equivalent layer approach, resulting in consistent levels, corrections that have not previously been applied. Additionally, we use the satellite data to its full spectral content, which helps to include India, where high resolution aeromagnetic data are not publically available. As India is located north of the magnetic equator, we also performed a variable reduction to the pole to the satellite data by applying an equivalent source method. The conformed aeromagnetic and satellite data are superimposed on a recent deformable Gondwana plate reconstruction that links the Kaapvaal Craton in Southern Africa with the Grunehogna Craton in East Antarctica in a tight fit. Aeromagnetic anomalies unveil, however, wider orogenic belts that preserve remnants of accreted Meso- to Neoproterozoic crust in interior East Antarctica, compared to adjacent sectors of Southern Africa and India. Satellite and aeromagnetic anomaly datasets help to portray the extent and architecture of older Precambrian cratons, re-enforcing their linkages in East Antarctica, Australia, India and Africa.

Assessing the rotation and segmentation of the Porcupine Bank, Irish Atlantic margin, during oblique rifting using deformable plate reconstruction

<p>With an increasing number of global and regional plate reconstruction models established in recent years, the motion of the Porcupine Bank, Irish Atlantic continental margin, underlain by orogeny-related pre-rift crustal basement terranes, have been investigated and restored as well.  However, these reconstructed models of the Porcupine Bank margin mainly depend on potential field data analysis and lack seismic constraints, failing to reveal the role of inherited crustal sutures during rifting and associated crustal deformation over geological time. In this study, five deformable models with distinct structural inheritance trends are established in GPlates by adjusting a previously published regional restoration model for the North Atlantic realm. For each model, driving factors (e.g., such as whether the Orphan Knoll is included, the altered rotational poles of the Flemish Cap, and the motion of the eastern border of the Porcupine Basin) are also taken into consideration. Crustal thicknesses from gravity inversion and seismic refraction data modelling are compared against those from these deformable plate reconstruction models to identify the most geologically reasonable one. The resulting preferred model has the Porcupine Bank subdivided into four blocks with each experiencing polyphase rotations and shearing prior to final continental breakup, implying strong inheritance and segmentation of the Porcupine Bank and the Porcupine Basin. The derived reconstructed paleo-positions over time of the Flemish Cap and the Porcupine Bank within the deforming topological network reveal new and evolving conjugate relationships during rifting, which are assessed using regional seismic transects from both margins. Finally, extensional obliquity between both margins is quantitatively restored, showing time-variant orientations due to the rotation and shearing of associated continental blocks, which contributes to unraveling the spatial and temporal evolution of southern North Atlantic rifting during the Mesozoic, prior to the initiation of seafloor spreading.</p>

Inherited lithospheric structures control arc-continent collisional heterogeneity

From west to east along the Sunda-Banda arc, convergence of the Indo-Australian plate transitions from subduction of oceanic lithosphere to arc-continent collision. This region of eastern Indonesia and Timor-Leste provides an opportunity for unraveling the processes that occur during collision between a continent and a volcanic arc, and it can be viewed as the temporal transition of this process along strike. We collected a range of complementary geological and geophysical data to place constraints on the geometry and history of arc-continent collision. Utilizing ~4 yr of new broadband seismic data, we imaged the structure of the crust through the uppermost mantle. Ambient noise tomography shows velocity anomalies along strike and across the arc that are attributed to the inherited structure of the incoming and colliding Australian plate. The pattern of anomalies at depth resembles the system of salients and embayments that is present offshore western Australia, which formed during rifting of east Gondwana. Previously identified changes in geochemistry of volcanics from Pb isotope anomalies from the inner arc islands correlate with newly identified velocity structures representing the underthrusted and subducted Indo-Australian plate. Reconstruction of uplift from river profiles from the outer arc islands suggests rapid uplift at the ends of the islands of Timor and western Sumba, which coincide with the edges of the volcanic-margin protrusions as inferred from the tomography. These findings suggest that the tectonic evolution of this region is defined by inherited structure of the Gondwana rifted continental margin of the incoming plate. Therefore, the initial template of plate structure controls orogenesis.