The evolution of oblique divergence along the Pacific‐North American plate boundary during the late Miocene is well‐preserved along the eastern margin of the Gulf of California. The early phase of ...this deformation occurred between ∼12.5 and ∼6 Ma in Sonora, NW Mexico, related to oblique rifting of the Gulf of California. The magmatic sequence for this period is exposed in the Cerro El Vigía, Guaymas region. This sequence is characterized by intrusive rocks, lava flows, and pyroclastic flows ranging in age from 12 to 10 Ma. The Cerro El Vigia has a predominant semicircular geomorphology traditionally ascribed to a volcanic caldera structure, such as large ring faults. Rock magnetic analyses of these magmatic products identify the magnetic minerals and their reliability for tectonic interpretations. The mean paleomagnetic direction from 14 sites from the Cerro El Vigia reveals up to 90° clockwise rotation about an inclined axis (65–85° axis plunge) with respect to stable North America. When interpreted in the context of the semicircular structure, these observations suggest that the structure has a tectonic, not volcanic origin. Paleomagnetic results and tectonics during the late Miocene suggest that this crustal block rotation corresponds to the development of large tension gashes deformed within a dextral transtensional system associated with continental deformation of the proto‐Gulf of California rift. Based on the paleomagnetic data, reported ages, and magmatic stratigraphy, we conclude that the magmatism and associated deformation at Cerro El Vigia was synchronous with transtensional tectonics between ∼11 Ma to ∼8 Ma.
Key Points
Paleomagnetism indicates clockwise vertical axis rotation up to 90° during late Miocene
The Cerro El Vigía correspond to large sigmoidal tension gashes
Magmatism and transtensional deformation are synchronous at Cerro El Vigia
Abstract
Active serpentinite mud volcanoes in the forearc region of the Izu‐Bonin‐Mariana system represent an excellent natural laboratory for studying the geochemical processes along convergent ...plate margins and the associated forearc. During IODP Expedition 366, serpentinite mud with lithic clasts from the underlying forearc crust and mantle as well as from the subducting Pacific Plate was recovered. Ultramafic clasts from Fantangisña Seamount reveal very high degrees of serpentinization with mesh and bastite textures as well as development of late lizardite and chrysotile veins, which suggests serpentinization temperatures below 200°C. On the other hand, recovered harzburgites and, on occasion, dunites from Asùt Tesoru Seamount show a well‐preserved primary assemblage with low degrees of serpentinization and forearc peridotite characteristics. Fine‐grained antigorite associating with lizardite has been identified throughout the serpentine mud matrix, suggesting an alteration temperature of c. 340°C. Furthermore, alteration conditions during rodingitization point to temperatures of at least 228°C, estimated via chlorite geothermometry. Additionally, a rare ophicarbonate clast containing andraditic as well as Cr‐rich hydrogarnets from Asút Tesoru Seamount indicates crystallization temperatures of at least 230°C. Hence, a trend of lower temperature of serpentinization and higher degree of alteration closer to the trench. The detailed characterization of the fluid‐rock alteration conditions as well as fluids composition and transport permits a better constraining of the fluid–rock interactions and related mass transfers within subduction zones and during ascent of serpentinite fault gouge within mud volcano conduits and in mudflows after their emplacement on the flanks of the edifices.
Plain Language Summary
The fluid migration and circulation in subduction zones play a crucial role in the geochemical cycling as well as the physical and mechanical processes taking place there. Characterizing their nature, source and pathways would contribute to a better understanding not only of the rheology and fluid recycling but also of the tectonic and metamorphic processes operating deep within the Earth's lithosphere as a whole. During an International Ocean Discovery Program (IODP) Expedition, 366 serpentinite mud volcanoes located on the fractured forearc of the Mariana subduction system were drilled. The recovered material consists of highly hydrated rocks that experienced varying degrees of metamorphism and alteration. Mineralogical and chemical composition study of these rocks showed that they are former mantle rocks formed by the infiltration of fluids within the subduction zone. Some of them experienced additional transformation during their ascent to the seafloor by acquiring substantial amount of CO
2
‐rich minerals. Furthermore, the results show a trend in which alteration temperature is decreasing but transformation degree is increasing with proximity to the subduction channel.
Key Points
Serpentinization and rodingitization in the subduction channel as well as carbonation in mud volcano conduits were identified
Overall evolution of the slab‐derived fluid was narrowed down to temperatures from c. 350° to c. 100°C and below
Serpentinization degree increases with proximity to the trench
•Air blast experiments were performed on flat steel plates.•Contains a review of 25 years of blast experimentation.•Dimensionless analysis is updated to include new data.•The post 1989 test data ...correlate with dimensionless analysis approaches.
In 1989, Nurick and Martin published two review papers on the deformation of thin steel plates subjected to impulsive air-blast loading. The state of the art has progressed significantly in the following 25 years, and this review paper restricts itself to experimental studies that investigate the response of monolithic metal plates subjected to air-blast loading generated by detonating plastic explosive. From the large number of experiments reported, it is shown that the failure progressions in circular and quadrangular plates are similar and can be adequately described by three “failure modes” – namely large plastic deformation (mode I), tensile tearing (mode II) and shearing (mode III) although the severity and location of these failures on the plates is primarily determined by spatial distribution of the blast loading across the plate surface, and that boundary conditions significantly influence the onset of shearing and tearing failures due to variation in the in-plane movement of the plate material. The non-dimensional analysis approaches used by Nurick and Martin have been expanded to include the effects of load localisation and stand-off distance, and show good correlation with the expanded sets of test data published since 1989. It is concluded that these approaches still hold merit as simple tools for evaluating the likely effect of a close proximity air blast load on a flat metal plate.
A new trigonometric shear deformation theory for isotropic and composite laminated and sandwich plates, is developed. The new displacement field depends on a parameter “
m”, whose value is determined ...so as to give results closest to the 3D elasticity bending solutions. The theory accounts for adequate distribution of the transverse shear strains through the plate thickness and tangential stress-free boundary conditions on the plate boundary surface, thus a shear correction factor is not required. Plate governing equations and boundary conditions are derived by employing the principle of virtual work. The Navier-type exact solutions for static bending analysis are presented for sinusoidally and uniformly distributed loads. The accuracy of the present theory is ascertained by comparing it with various available results in the literature. The results show that the present model performs as good as the Reddy’s and Touratier’s shear deformation theories for analyzing the static behavior of isotropic and composite laminated and sandwich plates.
The Greater Antilles islands of Cuba, Hispaniola, Puerto Rico and Jamaica plus the Virgin Islands host fragments of the fossil convergent margin that records Cretaceous subduction (operated for about ...90 m.y.) of the American plates beneath the Caribbean plate and ensuing arc‐continent collision in Late Cretaceous‐Eocene time. The “soft” collision between the Greater Antilles Arc (GAA) and the Bahamas platform (and the margin of the Maya Block in western Cuba) preserved much of the convergent margin. This fossil geosystem represents an excellent natural laboratory for studying the formation and evolution of an intra‐oceanic convergent margin. We compiled geochronologic (664 ages) and geochemical data (more than 1,500 analyses) for GAA igneous and metamorphic rocks. The data was classified with a simple fourfold subdivision: fore‐arc mélange, fore‐arc ophiolite, magmatic arc, and retro‐arc to inspect the evolution of GAA through its entire lifespan. The onset of subduction recorded by fore‐arc units, together with the oldest magmatic arc sequence shows that the GAA started in Early Cretaceous time and ceased in Paleogene time. The arc was locally affected (retro‐arc region in Hispaniola) by the Caribbean Large Igneous Province (CLIP) in Early Cretaceous and strongly in Late Cretaceous time. Despite multiple biases in the database presented here, this work is intended to help overcome some of the obstacles and motivate systematic study of the GAA. Our results encourage exploration of offshore regions, especially in the east where the forearc is submerged. Offshore explorations are also encouraged in the south, to investigate relations with the CLIP.
Key Points
We present an overview of the magmatism and metamorphism of the entire Greater Antilles Arc (GAA) convergent margin system
Prominent age interval from 95 to 60 Ma might relate to strong thermal/metamorphic events associated with the Caribbean Large Igneous Province
Immobile trace element geochemical data show that the GAA is dominated by mafic igneous rocks
Oceanic transform faults and fracture zones (FZs) represent major bathymetric features that keep the records of past and present strike‐slip motion along conservative plate boundaries. Although they ...play an important role in ridge segmentation and evolution of the lithosphere, their structural characteristics, and their variation in space and time, are poorly understood. To address some of the unknowns, we conducted interdisciplinary geophysical studies in the equatorial Atlantic Ocean, the region where some of the most prominent transform discontinuities have been developing. Here we present the results of the data analysis in the vicinity of the Chain FZ, on the South American Plate. The crustal structure across the Chain FZ, at the contact between ∼10 and 24 Ma oceanic lithosphere, is sampled along seismic reflection and refraction profiles. We observe that the crustal thickness within and across the Chain FZ ranges from ∼4.6–5.9 km, which compares with the observations reported for slow‐slipping transform discontinuities globally. We attribute this presence of close to normal oceanic crustal thickness within FZs to the mechanism of lateral dike propagation, previously considered to be valid only in fast‐slipping environments. Furthermore, the combination of our results with other data sets enabled us to extend the observations to morphotectonic characteristics on a regional scale. Our broader view suggests that the formation of the transverse ridge is closely associated with a global plate reorientation that was also responsible for the propagation and for shaping lower‐order Mid‐Atlantic Ridge segmentation around the equator.
Key Points
Fracture zones are represented by close to normal crustal thickness (∼5 km) that we attribute to the mechanism of lateral dike propagation
Major reorganization in plate motion represents a predominant factor in building transverse ridge at the Chain Fracture Zone
The analysis of our seismic data sets and interdisciplinary observations define lower‐order tectonomagmatic segmentation of the ridge axis
Nonlinear plate bending within Mindlin's strain gradient elasticity theory (SGT) is investigated by employing somewhat non-standard finite element methods. The main goal is to compare the bending ...results provided by the geometrically nonlinear three-dimensional (3D) theory and the geometrically nonlinear Reissner–Mindlin plate theory, i.e., the first-order shear deformation plate theory (FSDT), within the SGT. For the 3D theory, the nonlinear Green–Lagrange strain relations are adopted, while the von Kármán nonlinear strains are employed for the FSDT. The matrix-vector forms of the energy functionals are derived for both models. In order to perform the corresponding finite element discretizations, a quasi-C1-continuous 4-node tetrahedral solid element and a quasi-C1-continuous 6-node triangular plate element are employed for the 3D model and plate model, respectively. The first-order derivatives of the primal problem quantities are employed as additional nodal values to respond to the continuity requirements of class C1. A variety of computational results highlighting the differences between the 3D and FSDT models are given for two different plate geometries: a rectangular plate with a circular hole and an elliptical plate.
•Nonlinear finite element bending analysis is presented within the strain gradient elasticity.•The study aims to compare the differences between the three-dimensional (3D) theory and the Reissner–Mindlin plate theory.•Quasi -continuous tetrahedral and triangular elements are employed to present the finite element analysis.•The numerical results are given for two plate geometrs: a rectangular plate with a circular hole and an elliptical plate.
The Indonesia‐Australia‐New Guinea collision zone comprises a complex system of tectonic blocks whose relative motion accommodates convergence of the Sunda Block, Pacific, Australian, and Philippine ...Sea plates. Previous studies have considered either the western or eastern ends of this system, in eastern Indonesia and Papua New Guinea, respectively. However, these studies had limited ability to characterize either the kinematics of the central part of the system or transitions in tectonic regime across it. In this study, we perform a simultaneous inversion of 492 earthquake slip vectors and 267 GPS velocities to quantify the block movement spanning the Sunda‐Banda Arc, Western New Guinea, and Papua New Guinea. Our best‐fitting kinematic block model comprises 23 elastic blocks, for which we estimate the rotation rates and block boundary slip rates. We show how the Cenderawasih Bay sphenochasm was likely formed by a combination of both rotations (2.82 ± 0.11°/Myr anticlockwise) of the Bird's Head Block and southwest‐directed convergence (39.9 ± 1.7 mm/yr) along the Lowlands fault. Our estimated relative slip vectors across the New Guinea Fold‐and‐Thrust Belt indicate a transition in the tectonic regime of the block boundary from predominately thrust faulting at its western segment, with a convergence rate up to 19.5 ± 0.6 mm/yr, to predominately sinistral motion in the center segment with slip rate ∼7 mm/yr, and returning to thrust in the eastern segment with a convergence rate up to 9.0 ± 0.5 mm/yr, implying the combined effect of multiple driving mechanisms.
Plain Language Summary
The Indonesia–Australia–New Guinea collision zone is an east‐west elongated belt of complex tectonics at the northern edge of the Australian Plate, where the northward movement of the Australian continental lithosphere is accommodated by relative movement among a series of “microplates” in Indonesia and New Guinea. The interactions among these plates span the full gamut of tectonic phenomena. In this study, we use GPS measurements of crustal motion and earthquake data to estimate the motion of the tectonic units (plates and microplates) within the collision zone. While previous studies have considered either the western or eastern parts of this collision zone in isolation, in this study we consider together all the blocks spanning the zone from west to east. We show that this provides greater insight into changes in the tectonic regime through the center of the collision zone, and allows us to establish a new model for the development of the Cenderewasih Embayment in north‐central New Guinea.
Key Points
A new broad‐scale kinematic model has been developed spanning the 5,000 km length of the Indonesia‐Australia‐New Guinea collision zone
The evolution of Cenderawasih Bay is based on the joint effect of the rotation of the Bird's Head block and the WSW drift of Weyland Thrust
The New Guinea Fold‐and‐Thrust Belt experiences two transitions in its tectonic regime, as it traverses the center of the collision zone
The Lesser Antilles subduction zone marks the convergence between the Caribbean Plate and the oceanic Atlantic part of the America Plate. A specificity of this subduction is the development of a huge ...accretionary prism, the Barbados complex. As other subduction zones, the Lesser Antilles one has the potential to produce megathrust-associated earthquakes and related tsunamis. This study evaluates the potential hazard of tsunami scenarios along this eastern boundary of the Caribbean Plate, taking into account its specificities. We define six scenarios along the Lesser Antilles subduction zone including three
M
w
7.5
, 8.0 and 8.5 earthquake models, in both northern and southern parts of the arc. We incorporate in tsunami simulations the effect of sediment amplification in tsunami generation. In the southern half, the thick sediments pile, related to tectonic accretion, appears much more effective than the much thinner accumulation characterizing the northern half. The bed shear stress is also computed in this study as it is an important factor in sediment transport which can show the potential locations for sediment movement by tsunamis. Our results indicate the ability of scenario earthquakes to produce powerful tsunamis. The impacts of northern scenarios on Guadeloupe could be severe (maximum tsunami wave height of
>
5
m
), whereas the impacts from southern scenarios are relatively less strong (maximum wave amplitude of
<
5
m
). The tsunami waves produced by
M
w
8.0
and 8.5 appear able to inundate the coast of Sainte-Anne, Guadeloupe, up to
2
km
. The distributions of bed shear stress from northern scenarios suggest that the offshore Leeward Islands could be potentially prone to sediment transport as possible tsunami deposits have been found in the region in former geological studies.
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