Explore the vast range of titles available.

NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ~10 million years. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, the latter likely caused by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest impactor size-frequency distributions proposed for the Kuiper belt.

Five tectonic modes of mantle convection are obtained and analyzed with three-dimensional numerical models in a spherical shell domain. The five tectonic convective modes are non-plate mobile-lid, plate-like mobile-lid, episodic plate-like mobile-lid, episodic stagnant-lid, and stagnant-lid convective modes, respectively. The typical characteristics of these five tectonic modes and their numerical classification criteria based on plateness, mobility, and their standard deviations are presented and discussed. The results show that the yield stress of the lithosphere has profound effects on the tectonic convective modes. With the gradual increase of yield stress, the tectonic mode of mantle convection changes from one to another sequentially through the aforementioned five modes. Additionally, as the Rayleigh number increases, the range of yield stress for the platelike mobile-lid convective mode decreases, and the dimensionless transition stress between different tectonic modes increases. Specifically, the dimensional transition stress between the non-plate mobile-lid convective mode and plate-like mobile-lid convective mode increases with the increase of Rayleigh number, but decreases between other tectonic modes. Furthermore, we find that the transition stress between different tectonic modes is inversely proportional to the internal heating rate, with the transition stress decreasing as the internal heating rate increases. The fitting analysis of the transition stress between tectonic modes shows that Earth’s current plate tectonics correspond to a lithospheric yield stress of 150–250 MPa, which aligns with the strength of serpentinized mantle rock determined by experimental petrography. If the Archean mantle was 300°C warmer than it is today, then the Earth was in an episodic stagnant-lid convective mode. The tectonic evolution of the Earth’s surface is closely related to the lithospheric strength and the process of thermal evolution. If the lithospheric strength was only 150 MPa, plate tectonics in the early mantle rapid cooling model would have begun before 3.8 Ga, and plate tectonics in the late mantle rapid cooling model would have begun at approximately 1.5 Ga. However, at a lithospheric strength of 200 MPa, plate tectonics in the late mantle rapid cooling model would have begun later than 0.95 Ga, and plate tectonics in the early mantle rapid cooling model would have begun at approximately 2 Ga. The early Earth was in the episodic stagnant-lid convective mode, which means that subduction might still have occurred at that time. The presence of the episodic plate-like mobile-lid convective mode in Earth’s later history indicates that there might also have been intermittent surface stagnation during plate tectonics, which may provide an explanation for the quiet period of tectonic activity at approximately 1.0 Ga on Earth. This indicates that tectonic inactivity during a geological period is not an indicator that plate tectonics did not begin.

Arc volcanism across Iran is dominated by a Paleogene pulse, despite protracted and presumably continuous subduction along the northern margin of the Neotethyan ocean for most of Mesozoic and Cenozoic time. New U‐Pb and 40Ar/39Ar data from volcanic arcs in central and northern Iran constrain the duration of the pulse to ∼17 Myr, roughly 10% of the total duration of arc magmatism. Late Paleocene‐Eocene volcanic rocks erupted during this flare‐up have major and trace element characteristics that are typical of continental arc magmatism, whereas the chemical composition of limited Oligocene basalts in the Urumieh‐Dokhtar belt and the Alborz Mountains which were erupted after the flare‐up ended are more consistent with derivation from the asthenosphere. Together with the recent recognition of Eocene metamorphic core complexes in central and east central Iran, stratigraphic evidence of Eocene subsidence, and descriptions of Paleogene normal faulting, these geochemical and geochronological data suggest that the late Paleocene‐Eocene magmatic flare‐up was extension related. We propose a tectonic model that attributes the flare‐up to decompression melting of lithospheric mantle hydrated by slab‐derived fluids, followed by Oligocene upwelling and melting of enriched mantle that was less extensively modified by hydrous fluids. We suggest that Paleogene magmatism and extension was driven by an episode of slab retreat or slab rollback following a Cretaceous period of flat slab subduction, analogous to the Laramide and post‐Laramide evolution of the western United States. Key Points Iranian arc volcanism is dominated by a Paleogene flare‐up The volcanic flare‐up overlaps in time with a phase of extensional tectonism The extensional flare‐up is ascribed to Neotethyan slab rollback

Palinspastic map reconstructions and plate motion studies reveal that switches in subduction polarity and the opening of slab gaps beneath the Alps and Dinarides were triggered by slab tearing and involved widespread intracrustal and crust–mantle decoupling during Adria–Europe collision. In particular, the switch from south-directed European subduction to north-directed “wrong-way” Adriatic subduction beneath the Eastern Alps was preconditioned by two slab-tearing events that were continuous in Cenozoic time: (1) late Eocene to early Oligocene rupturing of the oppositely dipping European and Adriatic slabs; these ruptures nucleated along a trench–trench transfer fault connecting the Alps and Dinarides; (2) Oligocene to Miocene steepening and tearing of the remaining European slab under the Eastern Alps and western Carpathians, while subduction of European lithosphere continued beneath the Western and Central Alps. Following the first event, post-late Eocene NW motion of the Adriatic Plate with respect to Europe opened a gap along the Alps–Dinarides transfer fault which was filled with upwelling asthenosphere. The resulting thermal erosion of the lithosphere led to the present slab gap beneath the northern Dinarides. This upwelling also weakened the upper plate of the easternmost part of the Alpine orogen and induced widespread crust–mantle decoupling, thus facilitating Pannonian extension and roll-back subduction of the Carpathian oceanic embayment. The second slab-tearing event triggered uplift and peneplainization in the Eastern Alps while opening a second slab gap, still present between the Eastern and Central Alps, that was partly filled by northward counterclockwise subduction of previously unsubducted Adriatic continental lithosphere. In Miocene time, Adriatic subduction thus jumped westward from the Dinarides into the heart of the Alpine orogen, where northward indentation and wedging of Adriatic crust led to rapid exhumation and orogen-parallel escape of decoupled Eastern Alpine crust toward the Pannonian Basin. The plate reconstructions presented here suggest that Miocene subduction and indentation of Adriatic lithosphere in the Eastern Alps were driven primarily by the northward push of the African Plate and possibly enhanced by neutral buoyancy of the slab itself, which included dense lower crust of the Adriatic continental margin.

Insight into the evolution of Philippine Sea‐South China Sea (SCS) plate motions helps reveal the driving mechanisms of the long‐term tectonic complexity in Southeast Asia. Here, based on the integration of the most recent geological and seismic data, we present a new plate reconstruction model for this region characterized by back‐arc extension and subduction since the Eocene. We suggest that the western boundary of the Philippine Sea Plate was a constant sinistral strike‐slip fault at 55–22 Ma with a clockwise self‐rotation. The connection between the SCS and Shikoku Ridges possibly initiates at 30 Ma, when their spreading times overlapped indicating an affinitive origin and magma source. Regional‐scale geodynamic simulations interfaced with our reconstructed plate motion indicate that the seismic high‐velocity body under the SCS is likely to be the leading edge of the Pacific Slab. Plain Language Summary Since 55 million years ago, East Asia has been going through a complex plate recombination. Several quantitative plate motion models have been published, but there remain several irrationalities, for example, a footwall plate was moving away from the trench. We established a new model for the Philippine Sea‐South China Sea (SCS) region as an improvement. Our model provides a smooth movement of the Philippine Sea Plate (PSP) from the equatorial zone to its present position, with a clockwise rotation. Based on it, we deduce: (a) the western boundary of the PSP was a sinistral strike‐slip fault; (b) the spreading ridges in SCS and Shikoku Basin were connected at 30 Ma; (c) the stagnant slab under the SCS is a part of the subducting Pacific Slab. Key Points A new plate reconstruction model of Philippine Sea‐South China Sea (SCS) region since 55 Ma by integrating the latest geological geophysical data The western boundary of the Philippine Sea Plate was a constant sinistral strike‐slip fault at 55–22 Ma The geodynamic model indicates the seismic high‐velocity body under the SCS likely to be the leading edge of the Pacific Slab

The West European collisional Alpine belts are the result of the inversion, initiated in the middle Cretaceous, of the complex western Neotethys and the Atlantic continental rift domains and closure of remnants of Tethys between the North Africa and European cratons. While the kinematics of Africa relative to Europe is well understood, the kinematics of microplates such as Iberia and Adria within the diffuse collisional plate boundary is still a matter of debate. We review geological and stratigraphic constraints in the peri-Iberia fold-thrust belts and basins to define the deformation history and crustal segmentation of the West European realm. These data are then implemented with other constraints from recently published kinematic and paleogeographic reconstructions to propose a new regional tectonic and kinematic model for Western Europe from the late Permian to recent times. Our model suggests that the pre-collisional extension between Europe and Africa plates was distributed and oblique, hence building discontinuous rift segments between the southern Alpine Tethys and the Central Atlantic. They were characterised by variably extended crust and narrow oceanic domains segmented across transfer structures and micro-continental blocks. The main tectonic structures inherited from the late Variscan orogeny localized deformation associated with rifting and orogenic belts. We show that continental blocks, including the Ebro-Sardinia-Corsica block, have been key in accommodating strike-slip, extension, and contraction in both Iberia and Adria. The definition of a new Ebro-Sardinia-Corsica block allows refining the tectonic relationships between Iberia, Europe and Adria in the Alps. By the Paleogene, the convergence of Africa closed the spatially distributed oceanic domains, except for the Ionian basin. From this time onwards, collision spread over the different continental blocks from Africa to Europe. The area was eventually affected by the West European Rift, in the late Eocene, which may have controlled the opening of the West Mediterranean. The low convergence associated with the collisional evolution of Western Europe permits to resolve the control of the inherited crustal architecture on the distribution of strain in the collision zone, that is otherwise lost in more mature collisional domain such as the Himalaya. Les ceintures orogéniques alpines d’Europe occidentale sont le résultat de l’inversion, initiée au Crétacé moyen, de l’Océan Néotéthys occidental et des domaines du rift continental atlantique et de la fermeture des reliquats océaniques de la Téthys entre l’Afrique du Nord et les cratons européens. Si la cinématique de l’Afrique par rapport à l’Europe est bien comprise, celles de microplaques telles que Iberia et Adria, à l’intérieur de la limite de plaque, est encore débattue. Nous examinons les contraintes géologiques et stratigraphiques dans les ceintures orogéniques et les bassins péri-ibériques afin de définir l’histoire de la déformation et la segmentation crustale du domaine européen occidentale. Ces données sont ensuite intégrées avec d’autres contraintes issues de reconstructions cinématiques et paléogéographiques récemment publiées afin de proposer un nouveau modèle tectonique et cinématique régional de l’Europe occidentale, de la fin du Permien à l’actuel. Notre modèle montre que l’extension pré-collisionnelle entre la plaque Europe et la plaque Afrique était distribuée et oblique, à l’origine de segments de rift discontinus entre la partie sud de la Téthys Alpine et l’Atlantique Central. Ces rifts étaient caractérisés par une croûte variablement amincie et des domaines océaniques étroits segmentés à travers des structures de transfert et des micro-continents. Les principales structures tectoniques héritées tardi-varisques ont localisé les domaines d’amincissement et les orogènes. Nous montrons que plusieurs blocs continentaux, y compris le bloc Ebre-Sardaigne-Corse, ont joué un rôle clé dans l’accommodation des mouvements décrochants, de l’extension et de la convergence de l’Ibérie et d’Adria. De plus, nous montrons que l’existence de ce bloc permet d’affiner la relation tectonique entre l’Ibérie, l’Europe et domaine adriatique septentrional dans les Alpes. Au Paléogène, la convergence de l’Afrique referme les domaines océaniques à l’exception du bassin ionien. À partir de ce moment, la collision implique les différents blocs continentaux, permettant un transfert efficace de la déformation de l’Afrique vers l’Europe. La zone a finalement été affectée par le Rift Ouest Européen, à la fin de l’Eocène, qui a en partie contrôlé l’ouverture de la Méditerranée occidentale. La faible convergence associée à l’évolution orogénique de l’Europe occidentale permet de mieux comprendre le contrôle de l’architecture crustale héritée sur la distribution de la déformation dans la zone de collision, qui est autrement mal défini dans des domaines de collision plus matures tels que l’Himalaya.

The paradigm of plate tectonics holds that ocean plates are rigid during drift and only experience tectonic deformation at subduction zones, but new findings from the Pacific challenge this idea. Geological and geophysical evidence from the Ontong Java, Shatsky, Hess, and Manihiki oceanic plateaux indicates that extensional deformation during plate drift is a widespread phenomenon across the Pacific plate. These anomalously thick oceanic plateaux are weaker regions of the ocean lithosphere and more prone to tectonic deformation. Numerical geodynamic models demonstrate that a slab pull force from distant subduction plate boundaries can be effectively transmitted to oceanic plateaux through strong ocean lithosphere and cause substantial extension during plate drift. Our findings reveal that a wide expanse of the Pacific has experienced syn‐drift plate tectonics linked to pull from the western Pacific subduction factory. Plain Language Summary New findings from the Pacific Ocean challenge the conventional understanding of plate tectonics. It was previously believed that oceanic plates remained rigid during plate drift and only experienced deformation at subduction zones. However, geological and geophysical evidence from the Ontong Java, Shatsky, Hess, and Manihiki oceanic plateaux suggests that extensional deformation is a common occurrence during plate drift. These plateaux, which are weaker regions of the ocean lithosphere, are more susceptible to tectonic deformation. Through numerical geodynamic models, we have demonstrated that the slab pull force exerted by distant subduction plate boundaries can effectively cause substantial extension in these oceanic plateaux. This study reveals a significant presence of intra ocean plate deformation associated with the Western Pacific subduction factory. Key Points Seismic and petrologic data indicate that oceanic plateaux on the Pacific Plate are undergoing extensional deformation during plate drift Numerical modeling finds a slab pull force may be causing the extension as the force is transmitted far away from the subduction zone Oceanic plates can experience substantial tectonic deformation during their drift to subduction

In the upper crust, the chemical influence of pore water promotes time dependent brittle deformation through sub‐critical crack growth. Sub‐critical crack growth allows rocks to deform and fail at stresses well below their short‐term failure strength, and even at constant applied stress (“brittle creep”). Here we provide a micromechanical model describing time dependent brittle creep of water‐saturated rocks under triaxial stress conditions. Macroscopic brittle creep is modeled on the basis of microcrack extension under compressive stresses due to sub‐critical crack growth. The incremental strains due to the growth of cracks in compression are derived from the sliding wing crack model ofAshby and Sammis(1990), and the crack length evolution is computed from Charles' law. The macroscopic strains and strain rates computed from the model are non linear, and compare well with experimental results obtained on granite, low porosity sandstone and basalt rock samples. Primary creep (decelerating strain) corresponds to decelerating crack growth, due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep with apparently constant strain rate arises as an inflexion between those two end‐member phases. The minimum strain rate at the inflexion point can be estimated analytically as a function of model parameters, effective confining pressure and temperature, which provides an approximate creep law for the process. The creep law is used to infer the long term strain rate as a function of depth in the upper crust due to the action of the applied stresses: in this way, sub‐critical cracking reduces the failure stress in a manner equivalent to a decrease in cohesion. We also investigate the competition with pressure solution in porous rocks, and show that the transition from sub‐critical cracking to pressure solution dominated creep occurs with increasing depth and decreasing strain rates. Key Points Brittle creep is modeled with sliding winged cracks coupled to stress corrosion Trimodal creep curves can be reproduced A simple law for strain rate as a function of stress and temperature is derived

Metamorphic core complexes (MCCs) are interpreted as domal structures exposing ductile deformed high-grade metamorphic rocks in the core underlying a ductile-to-brittle high-strain detachment that experienced tens of kilometres of normal sense displacement in response to lithospheric extension. Extension is supposedly the driving force that has governed exhumation. However, numerous core complexes, notably Himalayan, Karakoram and Pamir domes, occur in wholly compressional environments and are not related to lithospheric extension. We suggest that many MCCs previously thought to form during extension are instead related to compressional tectonics. Pressures of kyanite-and sillimanite-grade rocks in the cores of many of these domes are c.  10–14 kbar, approximating to exhumation from depths of c.  35–45 km, too great to be accounted for solely by isostatic uplift. The evolution of high-grade metamorphic rocks is driven by crustal thickening, shortening, regional Barrovian metamorphism, isoclinal folding and ductile shear in a compressional tectonic setting prior to regional extension. Extensional fabrics commonly associated with all these core complexes result from reverse flow along an orogenic channel (channel flow) following peak metamorphism beneath a passive roof stretching fault. In Naxos, low-angle normal faults associated with regional Aegean extension cut earlier formed compressional folds and metamorphic fabrics related to crustal shortening and thickening. The fact that low-angle normal faults exist in both extensional and compressional tectonic settings, and can actively slip at low angles (< 30°), suggests that a re-evaluation of the Andersonian mechanical theory that requires normal faults to form and slip only at high angles ( c.  60°) is needed.

The South China Block was formed through the collisional orogeny between the Cathaysia Block and the Yangtze Block in the Early Neoproterozoic. The northern, western and southern sides of the South China Block were affected by disappearance of the Paleo-Tethyan Ocean during the Paleozoic. The southern and northern sides of the South China Block were respectively collided with the Indo-China Block and North China Block in the latest Paleozoic to form the basic framework of the Eastern China. The Eastern China has been affected by the westward subduction of the Pacific Plate since the Mesozoic. Therefore, the South China Block was influenced by the three major tectonic systems, leading to a superposed compound tectonics. The comparative study of the Mesozoic geology between the South China Block and its surrounding areas suggests that although the Mesozoic South China Block was adjacent to the subduction zone of the western Pacific, no juvenile arc-type crust has been found in the eastern margin. The main Mesozoic geology in South China is characterized by reworking of ancient continental margins to intracontinental tectonics, lacking oceanic arc basalts and continental arc andesites. Therefore, a key to understanding of the Mesozoic geology in South China is to determine the temporal-spatial distribution and tectonic evolution of Mesozoic magmatic rocks in this region. This paper presents a review on the tectonic evolution of the South China Block through summarizing the magmatic rock records from the compressional to extensional tectonic process with the transition at the three juncture zones and using the deformation and geophysic data from the deep part of the South China continental lithosphere. Our attempt is to promote the study of South China’s geology and to make it as a typical target for development of plate tectonic theory.