Plate Kinematics Research Articles

Kinematic reconstruction of the Raohe accretionary complex, Northeast China: Integration of onshore geologic evidence and global plate model

The Raohe accretionary complex (RHC) is located at the eastern of northeast China and adjacent to Russian Far East. As a part of the Circum-Pacific Orogenic Belt, it is the unique region of the accretionary orogenic belt, which is associated with the subduction process of the Panthalassic-Pacific Plate (PPP). We synthesize the detrital zircon ages of terrigenous clastic rocks of the RHC and tectonic units along the East Asian Continental Margin (EACM) to clarify its provenance. Then we place the docking position of the RHC adjacent to the South China Block, and determine that the final accretion of the RHC occur during the later Late Jurassic (~150 Ma) according to combination for ages of stitching plutons and terrigenous clastic rock. Integrating with the published global-scale plate kinematic frame, we restored the pre-docking motion path of the RHC using the Gplates software. The reconstructed scenario shows that it is a long distance of at least 1000 km between the proto-RHC and continent margin when the basaltic volcanism occurred subaqueously within the abyssal basin of the PPP. This model also provides a probability that the proto-RHC and the proto-Yuejingshan accretionary complexes have the same drift history, before their simultaneous emplacement into the continental margin.

ВНУТРИПЛИТНАЯ ВУЛКАНОТЕКТОНИЧЕСКАЯ АКТИВНОСТЬ В СЕВЕРО-ВОСТОЧНОМ И ЮЖНОМ СЕКТОРАХ ТИХООКЕАНСКОЙ ЛИТОСФЕРНОЙ ПЛИТЫ В СВЯЗИ С ИЗМЕНЕНИЕМ ЕЕ ОТНОСИТЕЛЬНОГО ДВИЖЕНИЯ

The analysis of altimetric data in combination with bathymetry and gravimetry materials in the north-eastern and southern sectors of the Pacific Ocean, as well as detailed data on the underwater relief, the structure of the sedimentary cover, the composition and absolute age of basalts obtained within the area of domestic geological exploration for ferromanganese nodules (the Clarion-Clipperton zone) is carried out. Structural trends formed by local cone-shaped local structures of presumably volcanic nature, grouped along transform faults belonging to various stages of the kinematics of the Pacific Plate, have been traced in the structure of the oceanic lithosphere at various scale levels. The first trend corresponds to the extension of the fault system corresponding to the spreading system on the crest of the East Pacific rise before the restructuring of its planned geometry in the Paleocene-Eocene, the second coincides with their extension after the change in the relative movement of the Pacific Plate. The trends are characterized by planned disagreement, and an increase in the number of seamounts is observed in the areas of their intersection. Within the area of detailed studies, obvious signs of volcanic-tectonic activity were revealed: high dissection of the underwater relief, hills of different heights with steep slopes, whose volcanic nature is confirmed by differentiated basalts raised from their slopes, the absolute age of which indicates the multistage outpourings that occurred in an intraplate environment. The angular velocity of rotation of the spreading axis and the linear velocity of its advance with changes in the kinematics of the Pacific plate are estimated and possible reasons for changes in its relative motion are considered. An improved scheme of adaptation of the spreading zone to a change in the direction of relative plate movement is proposed, acc0ording to which an essential factor of intraplate volcanic-tectonic activity is the relaxation of stresses in the plate caused by external influence on it.

Tilting of the Australian continent: New evidence from the subsidence and deposition history of the Northern Carnarvon Basin

Studies of global sea-level changes, plate kinematics, marine inundation, and morphology of the continental shelves suggest that the Australian continent has been tilting north eastwards since the Late Cretaceous. Here we investigate the direct impact of this phenomenon and the preceding tectonic events on the evolution of the Northern Carnarvon Basin and discuss their implications for hydrocarbon resources. We use backstripping and decompaction techniques to develop subsidence, sedimentation, and porosity evolution models for the basin, which sits on the axis of the tilt. The goal is to highlight the spatial and temporal variation of subsidence and sedimentation rates and assess their impacts on the porosity of the Early Cretaceous reservoirs within the basin, then give insights into the factors that created accommodation space for sediments. The results reveal a north-eastward shift of subsidence and sedimentation rates within the region. Thus, we observe the highest subsidence rates (∼90 m/Ma) in the southwest (Exmouth and Barrow sub-basins) from Early Jurassic to Early Cretaceous. In the Middle Cretaceous, subsidence and sedimentation moved north-east towards the Dampier (∼40 m/Ma) and some parts of the Barrow sub-basin (∼35 m/Ma). In the Cenozoic era, the highest subsidence rates moved further north-east towards the Beagle sub-basin (∼40 m/Ma) and the North Rankin platform. The results show that the Palaeozoic-Mesozoic rifting events produced higher tectonic subsidence (∼3 km) and higher sediment supply in the southwestern Exmouth and Barrow sub-basins, which reduced towards the north-east in the Dampier and Beagle Sub-basins (∼1.5 km). Subsidence plots along a NE-SW transect and the porosity evolution model results also demonstrate the tilting occurring in these sub-basins. We propose that mantle-driven and subduction-driven tilting of the Australian continent caused the observed local tilting of these sub-basins. Additionally, porosity evolution results provide further information for the definition of periods of hydrocarbon migration in the area.

Competition between 3D structural inheritance and kinematics during rifting: Insights from analogue models

AbstractThe competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these ‘internal’ and ‘external’ factors remain poorly understood, especially in 3D. In this study, we used brittle‐viscous analogue models to assess how multiphase rifting, that is changes in plate divergence rate or direction, and the presence and orientation of weaknesses in the competent mantle and crust, influences rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without any kinematic changes already creates complex rift structures. Divergence rates affect the strength of the weak lower crustal layer and hence the degree of mantle‐crustal coupling; slow rifting decreases coupling, so that crustal weaknesses can dominate deformation localisation and surface structures, whereas fast rifting increases coupling and deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle‐related deformation can overprint structures that previously formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle‐controlled towards crust‐controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are sufficiently well developed. We furthermore place our results in a larger framework of brittle‐viscous rift modelling results from previous experimental studies, showing the importance of general lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can produce a variety of deformation styles that may, however, lead to comparable end products. Therefore, careful investigation of the distribution of strain localisation, and to an equal extent of basin depocenter locations over time is required to properly determine the evolution of complex rift systems, providing an incentive to revisit various natural examples.

The Limpopo Magma‐Rich Transform Margin, South Mozambique: 1. Insights From Deep‐Structure Seismic Imaging

AbstractA variety of structures results from the interplay of evolving far‐field forces, plate kinematics, and magmatic activity during continental break‐up. The east Limpopo transform margin, offshore northern Mozambique, formed as Africa and Antarctica separated during the mid‐Jurassic period break‐up of the Gondwana supercontinent. The nature of the crust onshore has been discussed for decades in an effort to resolve issues with plate kinematic models. Two seismic refraction profiles with coincident multichannel seismic reflection profiles allow us to interpret the seismic velocity structures across the margin, both onshore and offshore. These seismic profiles allow us to (a) delineate the major regional crustal domains; (b) identify widespread indications of magmatic activity; and (c) map crustal structure and geometry of this magma‐rich transform margin. Careful examination of the profiles allows us to make the following observations and interpretations: (a) on land, continental crust is overlain by a >10‐km thick volcano‐sedimentary wedge related to an early rifting stage, (b) offshore, thick oceanic crust formed due to intense magmatic activity, and between the two (c) a 50–60‐km wide transform zone where the crustal structures are affected by intense magmatic activity and faulting. The prominent presence of intrusive and extrusive igneous units may be attributed to the combination of a deep‐seated melting anomaly and a trans‐tensional fault zone running through thinned lithosphere that allowed melt to reach the surface. A comparison of the crustal thinning along other transform margins shows a probable dependence with the thermal and/or tectonic history of the lithosphere.

Middle Miocene (∼14 Ma) and Late Miocene (∼6 Ma) Paleogeographic Boundary Conditions

AbstractDuring the Miocene, major global cooling occurred during two intervals: the middle Miocene (∼14–13 Ma) and the late Miocene (∼7‐6 Ma). The Antarctic Ice Sheet expanded substantially at ∼14–13 Ma, and glaciation in the Northern Hemisphere was initiated at ∼7–6 Ma. Although the causes of these two global cooling events remain unclear, paleoclimate modeling provides an important approach for investigating the mechanisms. However, paleoclimate modeling relies on paleogeographic boundary conditions, and many uncertainties remain regarding the land–sea distribution, topography, and bathymetry of the Miocene; specifically, previous published paleogeographic reconstructions for the middle and late Miocene show several discrepancies with each other. Here, we present two new sets of global topographic and bathymetric boundary conditions for the middle Miocene (∼14 Ma) and late Miocene (∼6 Ma). Our new reconstructions use a published plate kinematics model, oceanic lithospheric paleo‐ages, and oceanic sediment thicknesses and incorporate global fossil records, stratigraphy, lithofacies, paleoenvironment, and paleoelevation data. With these data, we further constrain the conditions of several important intercontinental and marginal seas surrounding Eurasia and the Arctic, the depth of major seaways in tropical latitudes and middle‐high latitudes of the Northern Hemisphere, and global paleotopography, especially that of the Tibetan Plateau and the Andes.

Effect of carbon nanotube-reinforced magneto-electro-elastic facings on the pyrocoupled nonlinear deflection of viscoelastic sandwich skew plates in thermal environment

This work presents a finite-element-based numerical formulation to evaluate the nonlinear deflections of magneto-electro-elastic sandwich skew plates with a viscoelastic core and functionally graded carbon nanotube-reinforced magneto-electro-elastic face sheets. Meanwhile, the proposed formulation accommodates the geometrical skewness as well. The magneto-electro-elastic sandwich skew plate is operated in the thermal environment and subjected to various multiphysics loads, including electric and magnetic loads. The viscoelastic core is modelled via the complex modulus approach. Two different forms of viscoelastic cores, such as Dyad 606 and EC 2216, are considered in this study. Also, different thickness configurations of core and facing arrangements are taken into account. The plate kinematics is presumed through higher-order shear deformation theory, and von Karman's nonlinear strain displacement relations are incorporated. The global equations of motion are arrived at through the total potential energy principle and solved via the direct iterative method. Special attention is paid to assessing the influence of pyroeffects, coupling fields and electromagnetic boundary conditions on the nonlinear deflections of magneto-electro-elastic sandwich plates working in the thermal environment and subjected to electromagnetic loads, which is the first of its kind. Also, parametric studies dealing with the skew angles, carbon nanotube distributions and volume fractions, thickness ratio, and aspect ratio have been discussed. The results of this work are believed to be unique and serve as a guide for the design engineers towards developing sophisticated smart structures for various engineering applications.

Australian Plate Subduction is Responsible for Northward Motion of the India‐Asia Collision Zone and ∼1,000 km Lateral Migration of the Indian Slab

AbstractDistributions of slabs within Earth's mantle are increasingly used to reconstruct past subduction zones, based on first‐order assumptions that slabs sink vertically after slab break‐off, and thus delineate paleo‐trench locations. Non‐vertical slab motions, which occur prior to break‐off, represent a potentially significant source of error for slab‐based plate reconstructions, but are poorly understood. We constrain lateral migration of the Indian slab and overlying India‐Asia collision zone by comparing tomographically imaged mantle structure with plate‐kinematic constraints. Following coupling of the Indian and Australian plates at the onset of collision, ∼1,000 km lateral migration of the Indian slab was driven by vertical subduction of the Australian slab. The sinking behaviors of individual slabs do not evolve in isolation, but instead influence, or are influenced by, other slabs in the same plate network. Hence, lateral slab migrations may be determined by interpreting the sinking behavior of slabs collectively, and with respect to plate kinematics.

Geodynamic and plate kinematic context of South China Sea subduction during Okinawa trough opening and Taiwan orogeny

The geodynamics and plate tectonics of the South China Sea (SCS)-Taiwan region since Miocene times are uncertain because the former extent and tectonic configuration of the subducted easternmost SCS along the Manila trench is uncertain. Here we unravel the regional kinematic context from main offshore constraints including published unfolding of the Manila slab from seismic tomography, which provides insight on restoring the subducted part of the SCS. We reconstruct a bayonet-shaped, stepped northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment we call ‘S3’, trending N070° that roughly parallels the present SCS shelf; a 350-km long ~N-S trending segment S2 that steps north to Hualien; and, a third segment S1 that extends from east of Hualien beneath the Ryukyu subduction zone trending N085° that ends near Miyako Island in the Ryukyus.The distance between present COB and S1 gives extension through time in the Okinawa trough, with a maximum of ~100 ± 20 km extension since late Miocene (10 Ma). We interpret S1 as a zone of weakness since ~18 Ma that ruptured from Miyako Island to east of Hualien as a tear fault, with the Huatung basin-Philippine Sea plate (HB-PSP) subducting northwestward between the two sides of the tear fault. The Manila transcurrent fault initiated ~18 Ma ago at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc, which began collision ~7 Ma ago along the EU margin. From ~7 to 6.5 Ma Taiwan was uplifted west of the Longitudinal valley. The Luzon arc and forearc basins were shortened within the Coastal range. Plate kinematic reconstructions from ~18 Ma to Present are synthesized in terms of continental or oceanic nature of the main PSP-HB and EU entities before their subduction that provide new understanding on Taiwan, PSP-SCS kinematics, and regional histories.

Analysis of thermal effect on buckling of imperfect FG composite plates by adaptive XIGA

This paper presents an effective computational framework based on adaptive extended isogeometric analysis (XIGA) for analyzing thermal buckling stability behavior of functional graded plates (FGPs) with flaws (e.g., holes, cracks). In this model, the locally refined non-uniform rational B-splines (LR NURBS), which can exactly represent the structure geometry and carry out the local refinement of the mesh, are used as the basis functions; and the first-order shear deformation theory is adopted to describe the kinematics of plates. According to the enhanced stresses on the mid-plane under the first critical buckling mode, a posteriori error estimator is evaluated. In addition, based on the posteriori error estimator, the meshes are automatically locally refined through refining the basis functions with large error. The obtained results illustrate the accuracy and reliability of the developed method, and show that the adaptive local refinement has better convergence ratio and higher computational efficiency than those of the uniform global refinement. Addressing the influence of some numerical aspects such as gradient index, direction and location of crack, and hole size on the critical thermal buckling temperature is also given.

Beyond ‘crumple zones’: recent advances, applications and future directions in deformable plate tectonic modelling

AbstractThe recent proliferation of deformable plate tectonic modelling techniques has provided a new direction in the study of plate tectonics with substantial implications for our understanding of plate deformation and past kinematics. Such models account for intraplate deformation, yet are highly variable in their inputs, capabilities and applications. The aim of this commentary is to review recent contributions to this topic, and to consider future directions and major omissions. Through this review it is apparent that the current published deformable models can be subdivided into those that as an input either: (1) solely use plate motions to drive deformation, or (2) require stretching or beta factor. Deformable models are resolving some outstanding issues with plate reconstructions, but major simplifications and modelling assumptions remain. Primarily, obtaining model constraints on the spatio-temporal evolution of deformation is an outstanding problem. Deformable plate models likely work best when the kinematics of smaller plates are included. However, questions remain regarding how to define such blocks, and their kinematic histories, whilst some work suggests that inclusion of such entities is negated through quantitative restorations.

Dynamics of the African Plate 75 Ma: From Plate Kinematic Reconstructions to Intraplate Paleo‐Stresses

AbstractPlate reconstruction studies show that the Neotethys Ocean was closing due to the convergence of Africa and Eurasia toward the end of the Cretaceous. The period around 75 Ma reflects the onset of continental collision between the two plates as convergence continued to be taken up mostly by subduction of the Neotethys slab beneath Eurasia. The Owen transform plate boundary in the northeast accommodated the fast northward motion of the Indian plate relative to the African plate. The rest of the plate was surrounded by mid‐ocean ridges. Africa was experiencing continent‐wide rifting related to northeast‐southwest extension. We aim to quantify the forces and paleostresses that may have driven this continental extension. We use the latest plate kinematic reconstructions in a grid search to estimate horizontal gravitational stresses (HGSs), plate boundary forces, and the plate's interaction with the asthenosphere. The contribution of dynamic topography to HGSs is based on recent mantle convection studies. We model intraplate stresses and compare them with the strain observations. The fit to observations favors models where dynamic topography amplitudes are smaller than 300 m. The results also indicate that the net pull transmitted from slab to the surface African plate was low. To put this into context, we notice that available tectonic reconstructions show fragmented subduction zones and various colliding micro‐continents along the northern margin of the African plate around this time. We therefore interpret a low net pull as resulting from either a small average slab length or from the micro‐continents' resistance to subduction.

Investigating the Plate Kinematics of the Bay of Biscay Using Deformable Plate Tectonic Models

AbstractThe plate kinematics of the Iberian plate and their implications on the plate tectonic evolution of the Bay of Biscay during rifting and subsequent opening of the southern North Atlantic continue to be topics of scientific discussion and debate. Constrained by previous plate reconstruction, geophysical, and geological studies, deformable plate tectonic reconstructions of the Bay of Biscay‐Parentis rift system are created in this study using the GPlates software. These deformable plate models are used to investigate the kinematics of the Landes High, Le Danois High, and Ebro Block previously recognized as independent continental blocks within deformable regions. A comparison between results calculated via deformable plate models with previously published and newly presented gravity inversion crustal thickness estimates provided a good metric for delineating the most probable plate kinematic scenario for the Bay of Biscay‐Parentis system and investigating the effect of the plate kinematic scenarios on the present‐day structure. The preferred plate kinematic model implies a transtensional Bay of Biscay‐Parentis rift system from the Jurassic to Early Cretaceous, with the onset of significant crustal thinning initiating during the Late Jurassic (∼150 Ma) induced by the motion of the Landes High and its interplay with the Ebro Block. Aside from demonstrating the role of the Landes High and its suggested interplay with structural inheritance on the deformation experienced within the Bay of Biscay, the timing and orientation of regional stress directions, and the velocities induced by the preferred deformable model provide good comparisons with previously calculated subsidence rates.

ГЕОДЕЗІЯ, КАРТОГРАФІЯ І АЕРОФОТОЗНІМАННЯ

The emergence of satellite observations was marked by their widespread use to determine the velocities and direction of horizontal motions of lithosphere plates (modern kinematics of lithosphere plates), which allowed to research the deformation processes at the global and regional levels. Today, permanent GNSS stations cover a large part of the land area. Since many of these stations have accumulated a large amount of daily observation over 20 years, it is possible to trace the deformation processes of certain areas. There is the problem of correct identification of observations of the true parameters of the deformation process. This issue requires the joint work of geophysicists and geodesists. But high-precision time series and values of GNSS station velocities are important and perspective data for the interpretation of geodynamic processes, which are much easier to obtain than geophysical or geological data, do not require special costs and should take into account their active development, the number of such stations is growing rapidly. Today, according to unofficial data, more than 300 reference stations operate in Ukraine. The aim of this work is to detect deformations of the Earth's crust in the Carpathian folded system using GNSS technology. The input data for the research were the observations over eight years (2013-2020) at reference stations in Ukraine (ZAKPOS network). From these observations, the combined solution (coordinates time series and velocities) was calculated using the scientific software GAMIT / GLOBK. According to the obtained data, the horizontal displacements vectors of GNSS stations were also constructed, and the deformations of the Earth's crust were calculated by the method of triangles, the vertices of which are GNSS stations, using the GPS Triangle Strain Calculator software. The calculated values of deformations showed a different geodynamic value, depending on the location of the triangles. In particular, the active zones of stretching (Rakhiv-Verkhovyna and Syanok-Ustryky-Dolishni) and compression (Rakhiv-Khust-Mukachevo) were identified. The research results make it possible to establish the features of the spatial distribution of crustal movement in the Carpathian region and in the future in a joint interpretation with geophysical data to create a regional geodynamic model of the Carpathian folded system.

Buckling of cracked FG plate resting on elastic foundation considering the effect of delamination phenomenon

The buckling analysis of cracked functionally graded material (FGM) plates resting on an elastic foundation taking into account the effect of the delamination of the elastic foundation is presented in this paper. The plate kinematics are based on the high-order shear deformation theory, the buckling of this cracked plate is computed by mixing the phase-field theory and finite element method (FEM), and material properties are assumed to vary through the thickness direction by a power-law distribution. The cracked FGM plate rests on the two-parameter elastic foundation, in which, the delamination areas are rectangular and circular. The accuracy of the present approach is proved by the comparison with published results. This paper also studies the effect of some parameters on the mechanic buckling behavior of the plate. The numerical results reveal that the delamination area and the crack length have a strong effect on the buckling loads as well as the buckling mode shapes of this plate.

The early drift of the Indian plate

Plate kinematic models propose that India and Sri Lanka (INDSRI) separated from Antarctica by extremely slow seafloor spreading that started in early Cretaceous times, and that a long-distance ridge jump left a continental fragment stranded off the Antarctic margin under the Southern Kerguelen Plateau 1-3. Here, we present newly acquired magnetic and deep wide-angle seismic data that require a fundamental re-evaluation of these concepts. The new data clearly define the onset of oceanic crust in the Enderby Basin and off southern Sri Lanka, and date its formation with unprecedented confidence. The revised timing indicates that India and Sri Lanka detached from Antarctica earlier in the east than in the west. Furthermore, no compelling evidence for an extinct spreading axis is found in the Enderby Basin. A refined plate motion model indicates that India and Sri Lanka departed from Antarctica without major rift jumps, but by the action of three spreading ridges with different timings and velocities that must have been accommodated by significant intracontinental deformation.

Nonlocal continuum damage modeling for functionally graded plates of third-order shear deformation theory

This article presents an effective computational approach that incorporates a quasi-brittle damage model into the isogeometric analysis of plates made of functionally graded materials. The plate kinematics is represented by a third-order shear deformation theory for higher accuracy. A coupling nonlocal equivalent strain field is introduced on the plate neutral surface to control the softening behavior. The utilization of the neutral surface in functionally graded plates enables the use of a single damage parameter over each plate cross-section. As a consequence, plate stiffness matrices can be calculated analytically, which simplifies the proposed damage model and its computer implementation. The discretization of the problem domain is based on basis functions generated from the non-uniform rational B-splines (NURBS) which are used for both geometric representation and field variable approximations, i.e., displacement and nonlocal equivalent strain. Owing to the high-order continuity of the NURBS basis functions, local features such as fracture damage zones can be resolved accurately. The performance of the proposed approach is demonstrated through several numerical examples under different loading configurations and compared with results from other approaches.

Cretaceous to Miocene NW Pacific Plate Kinematic Constraints: Paleomagnetism and Ar–Ar Geochronology in the Mineoka Ophiolite Mélange (Japan)

AbstractThe Mineoka Ophiolite Mélange is located at the intersection of the Pacific, Philippine Sea, Eurasian, and North American plates. The Mineoka ophiolite origin is disputed, and it has been ascribed to a fully subducted plate or part of the Pacific and Philippine Sea plates. In this paper, we present a kinematic reconstruction of the Mineoka Ophiolite Mélange and its relation with the Pacific Plate, based on new paleomagnetic data and bulk‐rock 40Ar/39Ar ages of basaltic rocks. In addition to standard analyses for paleolatitudes, we performed a Net tectonic rotation analysis on sheeted dolerite dikes to infer the paleospreading direction that formed the ophiolite. The analysis shows that 85–80 Ma MOR pillow basalts erupted at a paleolatitude of N ∼16°, whereas ∼50 Ma basalts formed at N ∼34°. Net Tectonic Rotation analysis suggests that the spreading direction was NE 60°. Ar–Ar ages yielded 53–49 Ma for MORBs and 41–35 Ma for island‐arc basalts. The formation of this ophiolite occurred in the back‐arc spreading of the Nemuro–Olyutorsky arcs of the NW Pacific. It infers that the final consumption of Izanagi below Japan instigated a subduction jump and flipped its polarity. Subduction initiated parallel to the ridge, and a piece of the original back‐arc crust got trapped near the Japan trench during the northwards motion of the Philippine Sea Plate. The contrasting motion between the Pacific and the Philippine Sea plates generated a highly unstable setting followed by a subduction zone that left a small‐sized and short‐lived plate (“Mineoka”), surrounded by subduction zones.

Kinematics of Deformable Blocks: Application to the Opening of the Tyrrhenian Basin and the Formation of the Apennine Chain

We describe the opening of back-arc basins and the associated formation of accretionary wedges through the application of techniques of deformable plate kinematics. These methods have proven to be suitable to describe complex tectonic processes, such as those that are observed along the Africa–Europe collision belt. In the central Mediterranean area, these processes result from the passive subduction of the lithosphere belonging to the Alpine Tethys and Ionian Ocean. In particular, we focus on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain. We divide the area of the Apennine Chain and the Tyrrhenian basin into deformable polygons that are identified on the basis of sets of extensional structures that are coherent with unique Euler pole grids. The boundaries between these polygons coincide with large tectonic lineaments that characterize the Tyrrhenian–Apennine area. The tectonic style along these structures reflects the variability of relative velocity vectors between two adjacent blocks. The deformation of tectonic elements is accomplished, allowing different rotation velocities of lines that compose these blocks about the same stable stage poles. The angular velocities of extension are determined on the basis of the stratigraphic records of syn-rift sequences, while the rotation angles are obtained by crustal balancing.

The challenge in restoring magma-rich rifted margins: The example of the Mozambique-Antarctica conjugate margins

Using the example of the conjugate Mozambique-Antarctica rifted margins, we investigate how mantle plume magmatism interacts with extensional processes during lithospheric rifting and breakup. The presence of extensive plume related magmatic additions formed during rifting masks the edges of the continental margins, making it difficult to determine a tight conjugate margin restoration and hindering the evaluation of their pre-breakup evolution. Based on rift domain mapping from seismic reflection interpretation, crustal thickness mapping using gravity inversion, lithosphere thinning from subsidence analysis, and the testing of different plate kinematic scenario, we develop a tight initial fit of the conjugate Mozambique-Antarctica margins and describe their evolution by a three stage model. These three stages consist of: i) during early rifting, the filling of accommodation space created by continental crust thinning with Karoo related magmatism resulting in a hybrid crust that maintains bulk crustal thickness producing shallow bathymetry or emergence and allowing SDR formation; ii) the decrease of magmatic budget relative to extension rates leading to bulk crustal thinning and increased bathymetries; and iii) the transition to seafloor spreading with a steady state magmatic budget resulting in normal thickness (6,5 ± 1 km) oceanic crust. This study not only adds new constraints on the regional breakup of Gondwana but also presents a new multidisciplinary methodology for restoring magma rich rifted margins formed in the presence of mantle plumes and for improving the understanding of the nature of such hybrid magma-rich crust.