Slab edges are a relatively common feature in plate tectonics. Two prominent examples are the northern end of the Tonga subduction zone and the southern end of the New Hebrides subduction zone. Near ...such horizontal terminations of subduction trenches, ongoing tearing of oceanic lithosphere is a geometric consequence. We refer to such kinks in the plate boundary as a Subduction-Transform Edge Propagator, or STEP. Other STEPs are the north and south ends of the Lesser Antilles trench, the north end of the South Sandwich trench, the south end of the Vrancea trench, and both ends of the Calabria trench. Volcanism near STEPs is distinct from typical arc volcanism. In some cases, slab edges appear to coincide with mantle plumes. Using 3D mechanical models, we establish that STEP faults are stable plate tectonic features in most circumstances. In the (probably rare) cases that the resistance to fault propagation is high, slab break-off will occur. Relative motion along the transform segment of the plate boundary often is non-uniform, and the STEP is not a transform plate boundary in the (rigid) plate tectonics sense of the phrase. STEP propagation may result in substantial deformation, rotation, topography and sedimentary basins, with a very specific time-space evolution. Surface velocities are substantially affected by nearby STEPs.
Seismic tomography models of the three-dimensional upper mantle velocity structure of the Mediterranean-Carpathian region provide a better understanding of the lithospheric processes governing its ...geodynamical evolution. Slab detachment, in particular lateral migration of this process along the plate boundary, is a key element in the lithospheric dynamics of the region during the last 20 to 30 million years. It strongly affects arc and trench migration, and causes along-strike variations in vertical motions, stress fields, and magmatism. In a terminal-stage subduction zone, involving collision and suturing, slab detachment is the natural last stage in the gravitational settling of subducted lithosphere.
In the mantle underneath the Tethyan suture zone, large volumes of positive velocity anomalies have been imaged by seismic tomography and interpreted as the present‐day signature of subducted Tethyan ...lithosphere. We investigate the Mesozoic‐Cenozoic subduction history of the region by integrating independent information from mantle tomography and tectonic reconstructions. Three different subduction scenarios for the Tethyan oceanic lithosphere, representative for the available tectonic reconstructions, are used to predict the present thermally anomalous volumes associated with the lithospheric surface subducted since the late Mesozoic. Next, these predicted thermal volumes and their expected positions are compared to the relevant anomalous volumes derived from seismic tomographic images. In this analysis we include, among others, the possible effects of ridge subduction and slab detachment after the Cenozoic continental collisions, absolute plate motion, and slab thickening in the mantle. Our preferred subduction model comprises the opening of large back‐arc oceanic basins within the Eurasian margin. The model points to slab thickening by a factor of 3 in the mantle, in which case the estimated volumes allow for active oceanic spreading (∼1–2.5 cm/yr) in the Tethyan lithosphere during convergence. Our results further indicate the occurrence of early Oligocene slab detachment underneath the northern Zagros suture zone, followed by both westward and eastward propagation of the slab tear and diachronous Eocene to Miocene slab detachment below the eastern to western Himalayas. Free sinking rates of the detached material of ∼2 cm/yr in the lower mantle provide the best fit between the tomographic mantle structure and our Tethyan subduction model.
Lipidation of transmembrane proteins regulates many cellular activities, including signal transduction, cell–cell communication, and membrane trafficking. However, how lipidation at different sites ...in a membrane protein affects structure and function remains elusive. Here, using native mass spectrometry we determined that wild‐type human tetraspanins CD9 and CD81 exhibit nonstochastic distributions of bound acyl chains. We revealed CD9 lipidation at its three most frequent lipidated sites suffices for EWI‐F binding, while cysteine‐to‐alanine CD9 mutations markedly reduced binding of EWI‐F. EWI‐F binding by CD9 was rescued by mutating all or, albeit to a lesser extent, only the three most frequently lipidated sites into tryptophans. These mutations did not affect the nanoscale distribution of CD9 in cell membranes, as shown by super‐resolution microscopy using a CD9‐specific nanobody. Thus, these data demonstrate site‐specific, possibly conformation‐dependent, functionality of lipidation in tetraspanin CD9 and identify tryptophan mimicry as a possible biochemical approach to study site‐specific transmembrane‐protein lipidation.
Lipidation of transmembrane proteins regulates many cellular activities, but whether this is site‐specific remains elusive. We revealed that lipidation of tetraspanin CD9 at three sites suffices for EWI‐F binding. Mutations to alanine reduced binding, whereas binding was rescued by tryptophans. Thus, we demonstrate site‐specific functionality of lipidation in CD9 and identify tryptophan mimicry as an approach to study site‐specific lipidation.
The eastern part of the Hellenic subduction zone is composed of the Pliny and Strabo “trenches” that have been regarded as a zone of convergence between the subducting African lithosphere and the ...overriding Anatolian–Aegean plate. In the Pliny and Strabo “trenches”, the oblique relative plate motion is generally thought to be accommodated by a typical strain partitioning consisting of strike–slip and convergence components. Notwithstanding the occurrence of strike–slip motion parallel with the Pliny–Strabo “trenches”, trench-normal thrusting is not observed so far. Therefore, we conducted a detailed analysis to investigate the deformation mechanisms of the eastern part of the Hellenic Trench system. Our analyses of offshore faulting and mechanisms of earthquakes in the overriding Aegean lithosphere show that the region of the Pliny and Strabo “trenches” obeys the mechanics of the sinistral shear zone model of Tchalenko (1970). We propose that the trench perpendicular convergence is taken up by the Rhodes fold and thrust belt, which has been postulated off the southeast coast of Rhodes. Several regional P-wave tomography results give indications of a slow seismic anomaly under this zone, which is interpreted as a tear between the Hellenic and Cyprus subduction zones. The primary reason for such tear and its propagation is the ongoing rollback of the subducted part of the African lithosphere, also referred to as “the Aegean slab”. Our work elucidates the surface expression of this tearing process in the form of the development of a shear zone between the Aegean lithosphere in the NW and the African lithosphere in the SE, the Pliny–Strabo Shear Zone.
•The Pliny–Strabo trench region is part of a large sinistral shear zone.•We address the genetic link between PSSZ and the deeper structure and processes.•PSSZ is the best example for deformation above a subduction tear so far.
Studies of intra‐ and inter‐plate deformation typically need a model describing the motions of the stable part of the tectonic plates for reference purposes. We have developed DEOS2k, a model for the ...current motion of seven major tectonic plates derived from space‐geodetic observations. This paper focuses on relative motion between Africa and Eurasia. In the past, this motion has been poorly established because of poor data coverage for Africa. DEOS2k is based on ITRF2000 Altamimi et al., 2002 and new African GPS observations. It is an improvement over the NUVEL‐1A model for predicting the present‐day relative motions of these two plates. DEOS2k predicts in northeastern Africa that Africa‐Eurasia relative motion is about 40% smaller in magnitude than NUVEL‐1A and trends more to the northwest. This is consistent with independent local geodetic observations. A similar shift in orientation, clockwise, is observed at the western tip of the plate boundary.
Marine gateways are important for semi-enclosed basins as they control exchange flows and influence water circulation. During much of the Early and Middle Miocene (~
23–13
Ma), the Paratethys (of ...which at present only the Black Sea and Caspian Sea remain) and the Mediterranean Sea were connected to both the Atlantic and Indian Oceans. The gateways to the Indian Ocean were closed ultimately in the Middle Miocene. Here, we apply an oceanic 4-box model to determine the temperature, salinity and exchange flows for the Paratethys and the Mediterranean Sea before and after closure of the Indian Ocean gateways. Our analysis forms a novel way of linking tectonics, climate and basin evolution. We investigate whether changes observed in the geological record of Paratethys are caused by changes in gateway configuration or in climate. We mainly focus on Paratethys which, because of the availability of a large variety of geological studies, presents an outstanding opportunity for studying the evolution of semi-enclosed basins and the impact of gateway closure. Moreover, Paratethys is considered to have played an important role in the evolution of Eurasian climate. Our analysis explores various values of the model parameters such as net evaporation and surface heat flux. Our main conclusions are: (1) Paratethys became more responsive to climate change after closure, (2) closure of the gateways to the Indian Ocean probably caused cooling of Paratethys and, in particular, accounted for the enigmatic Mid-Burdigalian cooling in Paratethys, (3) closure induced a change in salinity of Paratethys which is dependent on the net evaporation and size of the gateway connecting Paratethys to the Mediterranean, (4) Paratethys is sensitive to closure of both the gateway between Paratethys and the Indian Ocean, and the gateway between the Mediterranean Sea and the Indian Ocean, (5) Paratethys is influenced by the water properties of the Mediterranean Sea, (6) the water properties of Paratethys have only very limited influence on the Mediterranean Sea, and (7) in the advanced stage of the closure, the Mediterranean/Paratethyan temperature and salinity became more responsive to the restriction of the eastern gateways.
▶ We model paleoceanography of the Mediterranean/Paratethys in Early-Middle Miocene. ▶ This was the period in which closure of the gateways to the Indian Ocean happened. ▶ We investigate the effect of closure on circulation, salinity and temperature. ▶ Our results propose closure as the cause of Mid-Burdigalian cooling in Paratethys. ▶ We suggest using salinity to distinguish between the effects of gateways and climate.
We present a method to estimate the poorly understood mechanical coupling between lithosphere and underlying mantle, and apply it to the Eurasian plate. Mechanical equilibrium of tectonic plates ...requires the torque from mantle tractions (M) to be balanced by the torques from edge forces (E) and lithospheric body forces (B). The direction of E proves tightly constrained by plate boundary nature but B is affected uncertainties in the density structure of continents. We consistently find that the non‐zero torque required from mantle tractions does not agree with the orientation of any published absolute motion model. We conclude that mechanical balance of the Eurasian plate requires an actively convecting mantle, which should result in a torque on the Eurasian plate located in the southwest Pacific.
After their emplacement in the course of the late Mesozoic and the Cenozoic, the Hellenic nappes became fragmented during late orogenic extension since the late Eocene. Here we focus on the ...transition of underthrusting during nappe emplacement to exhumation during late orogenic extension. To this end, we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the Tripolitza and Ionian nappes, which were exhumed in the Cycladic and South Aegean windows, with newly obtained data on the sedimentary, stratigraphic, and structural development of the part of these nappes in the foreland, in front of the subduction thrust. The results allow the identification of two major events: Event 1 took place around the Eocene‐Oligocene transition and marks the onset of underthrusting of the Tripolitza nappe below the Pindos nappe and the Ionian nappe below the Tripolitza nappe, respectively. This led to the uplift and erosion of the Pindos unit and the onset of deposition of the Tripolitza and Ionian flysch in front of the Pindos thrust, together with the formation of mylonites at the base of the metamorphosed portions of the Pindos unit related to the underthrusting of the Tripolitza unit. Event 2 occurred in the latest Oligocene to earliest Miocene and marks the decoupling of the Ionian unit from the underthrusting plate, the accretion of the Tripolitza and Ionian units to the overriding plate, and the onset of late orogenic extension and exhumation in the overriding plate. This led to the formation of the South Aegean and Cycladic core complexes and the subsidence of the Klematia‐Paramythia half‐graben throughout the early Miocene.
The Carpathians orogenic system, with its along-arc variations in topography developed in the aftermath of continental collision, is associated with unusual foredeep basins, large-scale strain and ...seismicity concentration and high-velocity mantle bodies. The East Carpathians continental collision was non-cylindrical, leading to large-scale variations in thrust nappe kinematics, orogenic uplift patterns and foredeep subsidence, controlled by the mechanics and geometry of the lower plate. Thermo-mechanical modelling demonstrates that in this low-rate convergence regime, the subducted lithosphere had enough time to interact with the mantle to advance towards a thermal resettlement. This is favored by the low degree of metamorphism, mechanical weakness of the lower plate and the lack of active surface processes at the contact with and in the upper plate. In contrast, low-buoyant, thick lower crust and active surface processes keep the continuity of the slab intact and promote the development of typical foredeep basins. The model explains in a self-consistent manner the unusual geometry of the Vrancea seismogenic slab in the bend zone of the Romanian Carpathians. The model is also consistent with the presence of two high-velocity bodies inferred from seismic tomography studies and explains the depth zonation of seismicity in the Vrancea area. Differences between the northern part of East Carpathians and the southeastern bend of the Carpathians arc are largely controlled by lateral variations in crustal structure, topography emplacement and surface processes along the arc. Mechanical heterogeneity of the Carpathians subduction leads to the development of two end member modes of collision, allowing a study of these states and their transition. Lithospheric configuration and tectonic topography appear to be prime factors controlling variations in slab behavior. In the SE Carpathians, at the terminal phase of continental convergence, slab delamination, roll-back and depocenter migration appear to play a more limited role at shallow and lithospheric levels.
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